Nobel Prize Physics 2019

The Nobel Prize for Physics has been awarded this year to Jim Peebles for ” theoretical discoveries in physical cosmology” and to Michel Mayor and Didier Queloz for “the discovery of an exoplanet orbiting a solar-type star”.

It happens regularly that the Nobel Prize is split, but in this case there is hardly a connection between the two topics, and the Nobel committee must have realised that,  by adding that the prize this year was won for “contributions to our understanding of the evolution of the universe and Earth’s place in the cosmos”

In this post I will concentrate on Jim Peebles, maybe in a later post I will write more about the discovery of the other two physicists.

The scientific career of Peebles is closely associated with the Cosmic Microwave Background (CMB) radiation, so I will first explain what it is and how it was discovered.

According to the Big Bang theory, the Universe came into being 13.8 billion year ago. Incredibly tiny, hot and dense, it started to expand, while cooling. In the beginning it was a soup of gluons and quarks, but after a few minutes (!) the temperature had dropped so much that “normal” matter, like protons, neutrons and electrons became stable and even some light elements like deuterons and alpha particles could be formed. But it was still a plasma for many thousand years, until after around 380.000 years the universe had cooled so much that electrons and nucleons could form neutral atoms, like helium and hydrogen. From that time onwards until present photons could travel freely, the Universe had become transparent.

In the 1960’s Dicke and Peebles at Princeton studied this Big Bang theory, which was still not universally accepted at that time. If the Universe started with a “primordial fireball” , remaining radiation of this fireball should still be present. But the Universe has expanded about 1000 times since it became transparent, so the wavelength of that radiation has also increased 1000 times! No longer visible (reddish) light, but microwaves with a wavelength in the order of cm/mm’s, corresponding to a temperature of only a few Kelvin.

To detect this kind of radiation you need a microwave radiometer , and two colleagues of Dicke and Peebles, Roll and Wilkinson, also at Princeton, were building one. Then they learnt that two scientists at Bell Laboratories, Penzias and Wilson, only 60 km away from Princeton, were actually working wich such a radiometer and had found results they could not explain. Here is a photo of the Holmdel Horn Antenna, used by Penzias and Wilson.

What was it they could not explain? Well, measuring microwave radiation is not easy, because there is much “noise” from many sources, which you have to eliminate or take into account. What they found was that there always remained a background corresponding to a absolute temperature of 3.5 Kelvin. It did not matter which part of the sky they pointed the horn to, and whether it was day or night, there was always this background. They even cleaned the inside of the horn, removing pigeon droppings!

When the two teams came together, the solution was immediately clear. Penzias and Wilson had inadvertently discovered the Cosmic Microwave Background radiation, predicted by Dicke and his team. “Well, boys, we’ve been scooped “, Dicke supposedly said.

The two groups decided to write separate articles for the Astrophysical Journal of 1965, referring to each other. Cosmic Black-Body Radiation by Dicke, Peebles et al. and , very modestly titled, A Measurement of Excess Antenna Temperature at 4080 Mc/s by Penzias and Wilson.

In 1978 Penzias and Wilson received the Nobel Prize for Physics “for their discovery of cosmic microwave background radiation” Of course many in the scientific community found that the Nobel Prize should have been awarded to both teams. But (old fashioned) Nobel Prize rules made that impossible, teams can not get the Nobel Prize, only individuals (maximum three).

Roll and Wilkinson continued with their experiment and published the results the next year in the Physical Review Letters: ” Cosmic Background Radiation at 3.2 cm-Support for Cosmic Black-Body Radiation. Searching information for this post, I found a fascinating article, written a few weeks ago by Peter Roll, now retired of course, about his perspective on the 1965 discovery of the CMB. VERY readable, also for non-physicists.

I have written in some detail about the discovery of the CMB radiation because the importance of this discovery can hardly be overestimated. It changed the Big Bang theory from a controversial hypothesis into the standard model for the evolution of the universe. Here is another very readable article in Physics Today, one year after the discovery: A Bang, not a Whimper?

Of course there were still many questions. If the radiation was really thermal, it should have a well-defined spectrum. And it was of course very convincing that the radiation was the same at each point of the sky, but actually there should be minuscule differences, how else could stars and galaxies have formed, if the early universe was completely homogeneous?

The best way to investigate these questions, was to launch a spacecraft and observe the radiation outside Earth’s atmosphere. And that’s what happened. In 1974 NASA asked for scientific proposals and in 1989 the Cosmic Background Explorer (COBE) was launched. Two main experiments, FIRAS by John Mather, to determine the spectrum of the CMB radiation and DMR by George Smoot to measure the miniscule differences (the “anisotropy”) of the CMB.

Here is the spacecraft. Dimensions (without solar panels) ~ 4,5 x 2,5 m. The experiments are indicated, the Dewar contained liquid helium to cool especially FIRAS to near absolute zero temperature.

Here are the results. The CMB spectrum fits so perfectly the shape of a thermal source (“blackbody”) that it received a standing ovation when it was presented to the American Astronomical Society in January 1990.

The temperature of the CMB is 2.728 K, but Smoot found indeed tiny differences, depending on the location in the sky. Here is a map of the sky, with the temperature differences indicated in red (slightly warmer) and blue (slightly colder). When these results were published in 1992, they were frontpage news in the New York Times and Stephen Hawking in an interview called it “the greatest discovery of the century, if not of all times”.

In 2006 Mather and Smoot received the Nobel Prize for Physics “for their discovery of the blackbody form and anisotropy of the cosmic microwave background radiation”

Through the CMB we are looking back to the very young universe, 380.000 year old, before stars and galaxies were formed. Exploring these temperature differences, may help us to understand the evolution of the universe. But then a more detailed map of this anisotropy is needed!

In 2001 the Wilkinson Microwave Anisotropy Probe (WMAP) was launched. Until 2009 data have been collected, resulting in maps like this one, much more detailed.

And in 2009 the Planck observatory was launched. The instruments on board were cooled until 0.1 Kelvin, making it the coldest object in the universe..:-) Here is the Planck map, even more detailed.

You may wonder about the shape of these maps. It is called the Mollweide projection and it minimises the distortion you always get when you project a sphere on a plane. For comparison, here is the Mollweide projection of Earth.

There are two other discoveries in cosmology during the past 50 years that I have to mention, before I can finally come back to Jim Peebles and his Nobel Prize 🙂

The first one was the discovery of Dark Matter. In the 70s the American astronomer Vera Rubin studied the rotation of galaxies like the Andromeda galaxy and found that the outer regions of the galaxies were rotating much faster than expected, based on the visible matter of the galaxy and Kepler’s laws. An explanation could be that galaxies are surrounded by a halo of invisible (“dark”) matter. The existence of this Dark Matter has been widely accepted by the scientific community, but we still do not know yet what it is. According to many physicists, she deserved a Nobel Prize for her research, but she never got it. Because she was a woman? She passed away in 2016, Nobel Prizes can not be awarded posthumously. Here is a necrology: Vera Rubin, invisible to the Nobel Committee.

The second discovery was made in the 90s by two teams of astronomers who were studying the expansion of the universe. The Big Bang theory predicted that the expansion would slow down, because of the force of gravity. The crucial question was: will this force be big enough to stop the expansion, followed by a contraction, ending in a Big Crunch, or will the expansion go on forever. The result of their research was shocking: the expansion is not slowing down, but accelerating! There must be a repulsive force, which was called Dark Energy. Also here we do not know what it is. In 2011 the leaders of the two teams were awarded the Physics Nobel Prize “for the discovery of the accelerating expansion of the Universe through observations of distant supernovae”. I wrote a blog about it: Physics Nobel Prize (2011).

So, what did Jim Peebles discover? Nothing actually, and that may have been a reason that he received the Nobel Prize so late in life (he is now 84 year old) as the Nobel Committee has a preference for (experimental) discoveries.

But Jim Peebles rightly deserves the Nobel Prize because he has been instrumental in developing the theoretical cosmological framework for what is called physical cosmology. In 1982 he published a groundbreaking article about a cosmological model with dark matter in it and in 1984 an article in which he added the cosmological constant Λ (now called dark energy) to his model. This model , the Λ CDM  model, is at present the standard model of cosmology. For this work Peebles could (should) have been awarded the Nobel Prize many decades ago! Well, better late than never 🙂

With this Λ CDM model, using the properties of the CMB radiation and other experimental results, it is possible to determine how much normal matter, dark matter and dark energy there is in the Universe. The best fit to the (Planck) CMB data is obtained with the following values:

  • Atomic matter 4.9 %
  • Dark Matter 26.8 %
  • Dark Energy 68.3 %

Probably most of you will have seen this result. Everything we observe around us, our earth, the sun, the planets, the galaxies, it is only ~ 5% of our universe. About the other 95% we know basically nothing. Astonishing and mind-boggling.

Let me finish this post with two images. Below is an overview of the Big Bang expansion. The CMB is seen to the left, called the Afterglow Light Pattern. To the left you see “Inflation” and “Quantum Fluctuations”. The present theory is that in the first ~ 10−32 (!) second, the universe expanded exponentially. I don’t feel qualified to write a post about it, see the Inflation article in Wikipedia.

When the universe became transparent after 380.000 year, there were no stars and galaxies yet, the universe was dark, except for the afterglow! It took hundred millions of years, before the first stars were formed. More info in Wikipedia’s Chronology of the universe.

In 1980 Peebles published a book Large-Scale Structure of the Universe and that has always been his primary interest. There are about 200 billion galaxies in the observable universe, are they just randomly distributed? The answer is no, they are part of what nowadays is called the Cosmic Web. They are concentrated along filaments, with huge voids in between. In this artist impression, each light dot is a galaxy. Another mind-boggling image. 🙂 .

In 2013 I have written a post : Largest Structure in the Universe discovered, very readable if I may say so 🙂

APPENDIX

How is it possible to extract the values for dark matter, dark energy etc from a map of the sky with minuscule temperature differences?

The first step is to “translate” the temperature differences into what is called a power spectrum. The CMB map has cold and warm patches in various sizes. A power spectrum gives the intensity of these patches as function from their (angular) size.

Here is the power spectrum of the PLanck CMB map. The largest temperature fluctuations are found in patches of around 1 degree. Notice that the angular scale runs from left (large patches) to right (small patches). The red dots come from the CMB map. The green line is the best fit from the Λ CDM model, using the parameters given above.

Here is an instructive video, how the different parts of the power spectrum correspond from left to right to increasingly detailed structures.

The calculations are complex and need powerful computers.

In this simulation: Build a Universe you can play around with the various parameters. To run it on your computer, you need to have Flash installed. Not everybody will have Flash, so I have taken two screenshots. The first one, shows the “fit” for a universe with only normal matter. The second one uses parameters like given above.

Will an asteroid hit Earth?

Roughly 66 million years ago the Chicxulub asteroid with an estimated diameter of 10 km struck Earth at the Yucatan peninsula in Mexico. It caused an extinction of 75% of all plant and animal species, including the dinosaurs.

In 1908 the Tunguska meteorite exploded above a remote region in Russia, flattening about 2000 km² of forest. Ongoing discussion if it was a comet or an asteroid. Estimated size 30-80 m.

On 15 February 2013 an asteroid, size approximately 20 m, exploded at an altitude of ~ 30 km above the Chelyabinsk district in Russia. The shockwave caused substantial damage, many people were injured by broken glass.

And last few weeks there has been “alarming” news in the media about several “space rocks” threatening to collide with Earth and cause havoc. Foremost in this was the British tabloid Daily Express. Here are a few of its headlines (click on the image to see the corresponding article)

7 September:

Asteroid shock: NASA warns of ‘100 percent’ chance of asteroid impact

27 September:

Asteroid alert: NASA tracks three space rocks heading past Earth at once – Will they hit?

2 October:

Asteroid warning: NASA panic as four killer space rocks avoid horror impact with Earth

NASA panics, warning of a ‘100 percent’ chance of asteroid impact? Hm, time for a post about asteroids and their danger for Earth 😉

Asteroids are “small” rocky objects, billions of them, orbiting the Sun, most of them in the (main) Asteroid Belt, between the orbits of Mars and Jupiter. Small is relative, more than 150 million are larger than 100 meter and the largest asteroid, Ceres, has a diameter of 945 km! Notice the units, used in the picture below. One AU (Astronomical Unit) equals 150 million km, the average distance between Earth and Sun. This unit is often used for distances in the Solar System. For example, Mars orbits at a distance of ~ 1.5 AU around the Sun and the main Asteroid Belt is located between around 2.2 and 3.2 AU.

There are also asteroids outside the main asteroid belt, orbiting closer to the Sun. When their closest distance to the Sun (perihelion) is less than 1.3 AU , they are labelled Near Earth Asteroids (NEA’s). They are interesting for several reasons. One of them is the possibility of mining them in the future. Another is the possibility that a NEA could come so close to Earth that it might collide!

Starting in the 1990’s numerous surveys have been set up to discover and monitor NEA’s. During the last decade the Catalina Sky Survey and the Pan-STARRS surveys have discovered more than thousand NEA’s yearly and every day new ones are discovered. The basic technique is to compare pictures of the sky, taken on different dates and looking for “light points” that have moved, using automated software.

In the figure below the cumulative total is shown (October 2019), split according to the estimated size of the asteroid. Total: 21059 , Larger than 140 m: 8817, Larger than 1 km: 900 (10 October 2019).

Fortunately most of these NEA’s will never come so close to Earth that there is a risk of collision. A subcategory has been defined of Potentially Hazardous Asteroids (PHA), asteroids that come closer to Earth than 0.05 AU and are larger than 140 m. At the moment the number of PHA’s is about 2000. They are of course monitored more closely.

In the left graph the total number of PHA’s is given (from 1999 until September 2019. Each year ~ 100 new PHA”s are discovered. The right graph shows the number of PHA’s larger than 1 km. The last decade only a few more have been found.

Here is a graph showing the orbits of the ~ 1400 PHA’s known in 2013.

After this explanation about NEA’s and PHA’s, you might be a bit scared that the UK tabloids were right in their warnings about imminent asteroid collisions resulting in disasters.

Let’s have a look at Sentry, operated by CNEOS, the Center for Near Earth Object Studies (objects because both asteroids and comets are studied). It is a highly automated impact prediction system, that continually monitors the most current asteroid catalog for possibilities of future impact with Earth over the next 100+ years. At the moment of writing this post, it monitors 945 objects. The probability of impact and the impact energy result in a number on the Torino Scale, comparable with the Richter index for earthquakes.

Here is the reassuring result of Sentry: All the 945 objects have a Torino index 0 ! They form no risk for Earth in the next century.

A few comments

  1. Keep in mind that the Torino Scale is defined only for the next 100 years. There exists another scale, the Palermo scale, that is more sophisticated, with both negative and positive values. The result is the same: none of the objects have positive values.
  2. When a new NEA has been discovered, its orbit is not yet well defined. It happens quite regularly that temporarily such an object has a positive Torino/Palermo index. Subsequent observations reduce the index .
  3. Sentry monitors also NEA’s that are smaller than 140 m and therefore officially no PHA’s.
  4. Asteroids, smaller than ~ 20 meter, will disintegrate in the atmosphere, leaving a streak of light, a fireball.

Earth is continuously bombarded from outer space by rocky objects. Every year about 40.000 tonnes. Occasionally a small asteroid, more often remnants of a comet or an asteroid. They are called meteorites and will “burn” in the atmosphere. Here is a map of these fireballs, recorded between 1988 and present. Size and color of the circles indicate the energy of the impact. The large orange circle is the Chelyabinsk asteroid, mentioned in the introduction of this post.

So, what about the scaremongering articles in the media? Here are again the last two captions. In total seven space rocks, horror impacts, NASA panic.

NASA tracks three space rocks heading past Earth at once – Will they hit?
NASA panic as four killer space rocks avoid horror impact with Earth

Here are the 7 scoundrels: 2019 SH3, 2019 SN3, 2019 SP. 2019 SE8,
2019 SM8 , 2018 FK5 and 2019 SD8.

The last column gives the closest distance, expressed in the Lunar Distance (
384402 km) . The size is approximate (see appendix).

NameSizeClose approachDistancein LD
2019 SH3 ~ 27m 2019-Sep-30 01:371202.000 km3.1
2019 SN3 ~ 16m 2019-Sep-30 11:45845.000 km 2.2
2019 SP ~ 44m 2019-Sep-30 17:41 2540.000 km6.6
2019 SE8 ~ 5m 2019-Oct-01 13:56159.000 km 0.41
2019 SM8 ~ 15m 2019-Oct-01 15:12 1085.000 km2.8
2019 FK5 ~ 6m 2019-Oct-01 22:565094.000 km 13.3
2019 SD8 ~ 12m 2019-Oct-02 02:29 532.000 km 1.4

In an appendix of this post I will explain how you can extract these data from the invaluable CNEOS website. In case another alarmist article will published, you can check yourself if you have to get worried 🙂

All seven asteroids are NEA’s, but none of them are Potentially Hazardous Asteroids and NASA will not have panicked at all. Actually these events are common, the past year around 2400 NEA’s have passed Earth, 73 of them even closer than the Moon (like 2019 SE8 in the table above). About 370 of them were PHA’s, but none of them came closer than 7.4 LD’s

Let’s have a look now at the first article

Asteroid shock: NASA warns of ‘100 percent’ chance of asteroid impact

A ridiculous title but the content is much better. Although there are no PHA’s that will hit Earth in the next 100+ years, on a larger time scale it may happen, so humanity should be prepared for such a situation.

Here is a informative infographic created by ESA, the European equivalent of NASA. Notice in the bottom row, how many asteroids in the medium range (100-300 m) still have to be discovered: more than 80 %!

When a big PHA asteroid is discovered on collision course with Earth, there is basically only one realistic option to avoid a disaster: to deflect it. When you are able to do that (many) decades before its impact, a relatively small change in its course might be sufficient. Many ways to deflect an asteroid are described in this Wikipedia article: Asteroid impact avoidance . And bi-annually a Planetary Defence Conference is organized, the last one was held in May 2019, here is the report .

One section of this conference was dedicated to asteroid Apophis, of special interest to me, because I have published three blog posts about it in 2010-2012 😉 . For a while after its discovery in 2004, there was concern that this 370 m big rock might hit Earth in 2036, after a close encounter in 2029.
I wrote Will the Earth be hit by Apophis in 2036? followed by a (technical) post Again Apophis . In 2012 the winner of the yearly competition for students and young professionals Move an Asteroid had a winner who proposed to deflect Apophis by paintballing 🙂 My report Paintballing Apophis! explains how he wanted to do it.

Apophis is not a PHA anymore, but will still pass Earth on 13 April 2029 at the VERY short distance of 31.000 km (less than 0.1 Lunar Distance!), so at the conference there were numerous suggestions how to make use of this opportunity.

Here is a fascinating animation of Apophis, passing Earth on 13-4-2029 (click on the image). All the blue dots are man-made objects, orbiting Earth! The red dot orbiting Earth is the International Space Station.

As in earlier conferences, part of the program is a tabletop exercise about a hypothetical asteroid threat. The participants have to discuss how to respond, which action to take, etc. Very realistic, it reads like a thriller. Scroll down to page 31 of the (pdf) report. Here are the “press releases” given daily to the participants.

In the exercise, the participants decided to deflect the asteroid by using Kinetic Impactors, heavy spacecraft that crashes with high speed into the asteroid. It is the most common way to deflect an asteroid.

THEORETICALLY! Because this technique has not yet been tested in a real situation. Quite amazing, and a source of concern for many scientists.

Finally there is now one space mission in progress to test this kinetic impactor technique and I will end this blog with a description of the Asteroid Impact and Deflection Assessment (AIDA) mission.

The mission is a cooperation between NASA and ESA and the original plan consisted of two spacecraft, a large NASA impactor called Double Asteroid Redirection Test (DART) and an ESA spacecraft , the Asteroid Impact Mission (AIM), that would watch DART crashing into the asteroid and observe the immediate effects of the impact.

Target of the mission is the asteroid Didymos, a PHA with a diameter of ~ 800 m, discovered in 1996 as 1996 GT . Don’t be surprised, but it has actually a “moon”, nicknamed Didymoon, diameter ~ 170 m, orbiting Didymos in about 12 hours.

This was the original plan: December 2020 AIM was to be launched, to arrive at Didymos in May 2022. It would go in orbit around the asteroid and study Didymos and Didymoon.

Dart would be launched in July 2021, arrive at Didymos October 2022 and crash into Didymoon, while AIM was watching! After the crash AIM would measure the change in Didymoon’s orbit, to see if this Kinetic Impactor technique is an effective way to deflect dangerous asteroids in the future.

Here is an artist impression of the mission.

And here is a very informative video, prepared by ESA in 2016 about AIM

But in December 2016, AIM was cancelled by ESA, after Germany withdrew the 60 million Euro funding for the project, to use the money instead for the ExoMars project. The Washington Post commented : Europe will send a rover to Mars but won’t protect Earth from an asteroid and a planetary scientist said “A cool project has been killed because of a lack of vision – even short term – and courage, and this is really sad

NASA decided to continue with the DART mission and measure the effects of the impact on Didymoon using earth-based telescopes instead. And ESA is planning to launch a much simpler spacecraft, named HERA, in 2023, after the crash of DART! After arrival at Didymos it would study the effects on Didymoon. But the decision to actually fly the mission still has to be taken, in November this year.

As an European I feel rather ashamed that Europe has acted this way.

x x x x x x x x x x x

Appendix

In this appendix I will explain how you can find reliable information about any asteroid, when you know its name.

First the naming convention for “minor planets” . The year of discovery is followed by two letters and (sometimes) a number. The first letter gives the half-month in which the object was first observed. The second letter stands for a number 1 until 25. (the I is left out to avoid confusion with the J) and counts the objects, discovered in that half-month. When the system was introduced, probably it was thought that there would not be more than 25 objects discovered in a half-month. But nowadays hundreds of objects are discovered every month! The number tells how many times you have to repeat the alphabet! Here is the coding table.

An example. Recently a NEO has been discovered: 2019 SP3. In the table we see that the S stands for 16-30 September and the P for 15. So this asteroid is the 3 x 25 + 15 = 90th object, discovered in the second half of September 2019.

To find the properties of this asteroid we go to the JPL Small-Body Database Browser. Enter the name 2019 SP3 (case sensitive) in the Search box.

Lots of information, mostly about the orbit (left table) and the discovery history (upper right table). Important for us are two numbers in the other tables, the MOID = 0.00252421 AU and the absolute magnitude H =26.98.

The minimal orbit intersection distance (MOID) tells us how close the orbits of 2019 SP3 and Earth can get. 0.00252421 AU = 378000 km. Less than the distance between Earth and Moon!

The absolute magnitude H indicates how bright the asteroid is. It gives us an indication about the size of the asteroid. A large asteroid will reflect more sunlight and therefore appear brighter. But this reflection also depends on the structure of the asteroid, is it coal black or more shining. This reflection property is given by the albedo , which can have a value between 0 (no reflected light) and 1 (perfect reflection).

The problem is that we have to guess what the albedo of our asteroid is. In general they are quite dark, with albedo between 0.3 and 0.05. Often a value of 0.15 is used.

Here is part of the conversion table :

Using the value of H =26.298, we find that the size of 2019 SP3 lies between 14 and 34 meter, with a probable value of 19 m.

Conclusion: with an estimated size of 19 m and a minimal distance to Earth of 378000 km, 2019 SP3 is NOT a PHA.

This is what the Daily Express reported:

Potentially hazardous’ space rock to fly closer to Earth than Moon

Precession of the Equinox

Don’t be put off by the title of this blog, I’ll try to keep it simple 🙂

In Greek/Roman times it was thought that Earth was the center of the Universe. The Sun , the planets, the stars were all rotating around Earth.

Now we know that Earth itself is rotating, in 24 hours (although we keep saying that the sun rises in the East and sets in the West).

We also know that Earth is orbiting around the Sun in 365 days. As seen from Earth, the Sun seems to be moving across the sky. This apparent path of the Sun throughout the year is called the ecliptic.

If Earth would be rotating like in the picture below, then during the whole year, the Sun would be above the Equator and there would be no seasons. . Day and night would be both 12 hour, everywhere on Earth, throughout the year.

But everybody knows that this is not the case. In the Northern hemisphere. daylight will be longer than night in summer and shorter in winter, whereas in the Southern hemisphere it is just the other way around. The reason is that the axis of rotation of the Earth is slightly tilted, about 23.5° .

Notice that during Earth’s orbit, the direction of the rotation axis remains the same (pointing to the North Star).

In the picture below we can see what happens in a bit more detail. Let’s start with the 1st Day of Spring (20/21 March), when the tilt is not directed towards the Sun and the Sun is directly over the equator. Day and night are equally long all over Earth, it is called the March Equinox. The same happens on the 1st Day of Autumn (22/23 September), the September Equinox.

From March until June, the Sun moves North, days become longer and nights shorter until the 1st Day of Summer, 21/22 June, the Summer Solstice, after which the Sun moves back to the Equator. From September to December, the Sun moves South, days become shorter and nights longer, until the 1st Day of Winter, 21/22 December, the Winter Solstice, after which the Sun moves back again to the Equator. All this has been described from the perspective of the Northern Hemisphere. For the Southern Hemisphere everything is opposite.

So the axial tilt of Earth is responsible for the seasons and there are scientists who believe that this tilt has been critical for life: Axis Tilt is Critical for Life , but this is quite controversial.

Until now I have been rather vague about the apparent position of the Sun. “Above the Equator”, “moving North”, “moving South”. Actually, we can be much more precise nowadays, using a coordinate system similar to what we use on Earth, with latitude and longitude. But how did the Greek and Romans do that?

To describe the location of the Sun against the backdrop of stars, the Greeks used the concept of constellations, patterns of stars that were given a name, often based on their myths and religion. A constellation most of you will know is Orion, the mythological Greek hunter. The left photo was taken by the Hubble telescope and shows the characteristic shape of Orion. Right an antique star chart, published in 1824. To guide the eye, I have connected the main stars with blue lines

During a year, the Sun crosses twelve of these constellations , as indicated in the image below. These twelve constellations are called the Zodiac. The names of the constellations may be familiar to you, if you know your (Western) horoscope 😉 .

At the moment that this post has been published , the Sun has left the Leo constellation and entered Virgo.

Nowadays many more constellations have been defined (88!), covering the whole sky. Below you see a map of the celestial globe. The Celestial globe is similar to the Earth globe, but everything is projected to the “sky”.

Notice that the horizontal scale (Right Ascension) is not in degrees, like longitude on the Earth globe, but in hours and going from right to left. Same as on the Earth globe the choice of the origin (zero) is arbitrary. On the Earth globe it is the Greenwich meridian, on the Celestial Globe it is the March Equinox. The traditional name for this origin is the First Point of Aries.

The name was coined by the Greek astronomer Hipparchus, who lived from c 190 BC until c 120 BC. At that time the Sun had just entered the Aries constellation during the Spring Equinox. The March Equinox is indicated by the Aries symbol ♈︎ .

The ecliptic is shown, with the constellations (in white) which the Sun is passing throughout a year. Following the ecliptic from right to left, you will notice that it starts at 0h in Pisces, the Sun moves North until 6h (Gemini) then back to the equator at 12h (Virgo), going down South until 18h (Sagittarius) and back to Pisces for the next cycle.

Do you notice the contradiction? The First Point of Aries is now located in Pisces! How can that be? Time to talk about the Precession of Earth!

Above I wrote that the rotation axis of Earth, during its orbit around the Sun, is always pointing in the same direction (to the North Star). That is correct at the moment, but not forever, because there is a third movement of Earth.

Probably many of you have been playing with spinning tops. When a top (or a gyroscope) is spinning, it will often “wobble” under the influence of the force of gravity. The same happens with the Earth under the influence of the gravitational force of Sun and Moon. This wobble is called Precession.

Here is a short video about the precession of a gyroscope

The Precession of Earth is a very slow process. One round takes about 25800 year. Here is an animation of the process.

The red line connects the two equinoxes, the March Equinox is marked with the Aries symbol. Notice how the March Equinox passes all signs of the zodiac during one precession. 360° in ~ 25800 year, means a shift of 1° every 72 year. Since Hipparchus’ time, the First Point of Aries has shifted ~30° , it is no longer in Aries, but in Pisces and will cross over to Aquarius
around 2600 AD.

The second part of the video shows how the North pole points to different stars during a precession. In the picture you see that “today” it is pointing at Polaris (the North Star) , but in 3000 BC it pointed at the star Thuban, and in 14000 AD it will point close to the bright star Vega.

To summarise, here is a picture, with the three movements of Earth, the daily rotation (24 hours), the yearly orbit around the Sun (~365 days) and the precession of the rotation axis (~25800 years).

Notice that the rotation of Earth and its orbit around the Sun are counterclockwise , while the precession is clockwise! So the yearly motion of the Sun through the Zodiac goes from Pisces to Aries to Taurus etc. But the Spring Equinox has, since Hipparchus , shifted back from Aries to Pisces and will shift to Aquarius around 2600 AD.

Let me end this post with some explanation about why I decided to write it.

Everything written above belongs to the realm of astronomy. Unfortunately there exists also astrology, a pseudoscience. Basically astrology states that the position of the heavenly bodies affects our lives. For example, an important factor is the location of the Sun on the day that you were born. That becomes the sign of your horoscope. Here is an example:

I was born on 17 April, therefore I am a Ram. But that is nonsense, maybe true in Hipparcos’ time. Because of the precession I was actually born when the Sun was in Pisces (12 March – 19 April)

Of course astrologers are aware of the precession, see for example
Sidereal and Tropical Astrology. for various “solutions”.

Directly related to precession is the concept of Astrological Ages. As explained above, during one precession of 25800 year, the March Equinox traverses all 12 signs of the Zodiac, staying in one sign on average 2150 year. Such a period is called an Astrological age. At the moment we live in the Age of Pisces.

Astrologers claim that each age is characterised by certain properties. For example the Age of Pisces is the age of religion, the Age of Aries was the age of war and the coming Age of Aquarius will be the age of freedom.

You will not be surprised that in my opinion these Astrological Ages are even more nonsense than horoscopes.

A few months ago a friend told me about Matias de Stefano, who calls himself an Indigo Child and has memories from an earlier life in Atlantis. He is 29 year old and has many followers. I listened to his video lecture Total Recall. Here is a transcription. One quote to give you an impression of the lecture:

We are Beings (indigo/crystal) that come from the 6th to 13th dimension, to try to promote the 4th and 5th dimension inside the 3rd.

But the following statement is so ridiculous that I decided to write this post.

Earth spins around the sun in a process which lasts about 365 days, but at the same time, our Sun spins around another sun which is a lot bigger, called Syria, about every 26,000 years. As a year on Earth, the Sun’s year has its seasons, equinoxes, solstices and ages, too.

Apparently he has not the faintest idea what the Precession of the Equinox means.

I will end this post with a famous song from the 1967 musical Hair. ” This is the dawning of the age of Aquarius “

A Pale Blue Dot

On  December 7, 1972, the crew of the Apollo 17 spacecraft, on their way to the Moon, took a picture of Earth at a distance of about 29,000 kilometers. It has been named The Blue Marble and is one of the most reproduced images in history.

Five years later, in 1977, NASA launched the Voyager 1, to explore the outer solar system. It was a highly successful mission with flybys of Jupiter, Saturn and Titan, Saturn’s largest moon.

After completion of this primary mission and before leaving the Solar System, it was suggested by astronomer and author Carl Sagan, that the Voyager 1 should look back and take one last picture of Earth. This picture was taken on  February 14, 1990 at a distance of about 6 billion km from Earth. The picture has been named the Pale Blue Dot , because in this picture Earth is not more than a single pixel. You may have to click on the picture to enlarge it and see Earth more clearly. The coloured bands are artefacts, caused by reflection of sunlight in the camera.

Inspired by this picture Sagan wrote the book Pale Blue Dot in 1994. Here is a quote from this book:

Look again at that dot. That’s here. That’s home. That’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every “superstar,” every “supreme leader,” every saint and sinner in the history of our species lived there–on a mote of dust suspended in a sunbeam.

I have used the Blue Marble image for a long time as background on my monitor screen. Recently I have changed it to the Pale Blue Dot.

At the moment Voyager 1 is still (partly) operational at a distance of about 22 billion km from the Sun, speeding away at more than 60.000 km/h.

Solar System Explorers

In this blog I will give updates about three space exploration missions described in earlier posts and report about two new ones.

New Horizons

I will start with New Horizons . In Close Encounter with Pluto I described how this spacecraft had a successful flyby with minor planet Pluto on 14 July 2015 and in an update New Horizons that it was on its way to 2014 MU69  , an object in the Kuiper belt.

A few days ago, on 1 January 2019, it had a flyby of Ultima Thule, as
2014 MU69 has been nicknamed. The distance between Earth and Ultima Thule is at the moment 6.6 billion km, never before has there been a close encounter at such a huge distance! (Distances in the picture are expressed in Astronomical Units, 1 AU = 150 million km)

During the brief flyby, New Horizons collected about 7 gigabytes of data, which in the coming months will be sent back to Earth. Radio signals take more than 6 hours to reach Earth, the 15 Watt transmitter can send ~ 500 bits per second, it may take 20 months.

Here are the first images. Left a vague color image, middle a more detailed black and white one, right the merger of the two, a kind of reddish snowman, size about 31 km. As was already expected, Ultima Thule is a so-called contact binary, it consists of two halves, now dubbed Ultima (the larger one) and Thule.

Mars InSight

A few months ago I wrote a blog Landing on Mars, about the Mars InSight spacecraft. Mission of this spacecraft is to study the interior structure of Mars. It has now deployed the seismometer, to detect Marsquakes.

Next month InSight will start drilling into the surface of Mars.

Hayabusa2

As I reported in my blog Hayabusa2 , it came as a surprise that the surface of asteroid Ryugu was very rough and rocky. Here is a picture of Ryugu’s surface.


The first sampling touchdown, scheduled for October, was postponed until at least the end of this month. The engineers are still studying how to land the spacecraft safely.

The two tiny hopping Minerva rovers are still working correctly and have been renamed Hibou (French for Owl) and Owl. If you are curious about the reason, read this: Naming our MINERVA-II1 rovers 😉 .. Don’t think that scientists have no sense of humor 😉

Osiris Rex

When I wrote my blog about Hayabusa2, I was unaware of another mission to send a spacecraft to an asteroid, collect some material and bring it back to Earth. It is an American one, the Osiris Rex mission. Here is some information:

Launched 8 September 2016 with as destination the asteroid 101955 Bennu. Bennu is even smaller than Ryugu, about 500 m diameter. In December 2018 Osiris Rex reached Bennu and on 31 December it fired its thrusters to go into orbit. It will remain there for the next two years, studying the asteroid and it will try to acquire at least 60 gram of regolith (the surface material of Bennu) in a procedure very similar to Hayabusa’s.

Here is an artist impression of Osiris approaching Bennu, with the sampler horn extended.

And here is an image of Bennu, taken by Osiris.

Planned return date is 24 September 2023.

One aspect of the mission is worth mentioning here. OSIRIS is an acronym for Origins, Spectral Interpretation, Resource Identification, Security. Why security? Because Bennu is a potentially hazardous object, it is possible it might hit Earth in the future. Don’t worry, not in our time, but possibly between 2175 and 2199. The uncertainty is there because the orbits of these “small” asteroids are influenced by many factors, for example the disturbing influence of the other planets. But also the effect of heating and cooling by the sun light, the Yarkovsky effect  and it is this effect that Osiris will study. (Forget about this if you find it too complicated… 🙂 )

Chang’e-4

China confirmed its role as global player in space exploration on 3 January 2019, when it landed for the first time in history a spacecraft on the far (“dark”) side of the Moon. The Chang’e 4 was launched on 7 December 2018 and consists of a lander and a rover, the Yutu-2. The set-up and landing procedure were similar to the Mars Pathfinder mission, after a powered descent of the lander to the Moon surface, the rover rolls down a ramp (see my Landing on Mars post).

Here is an image of the Yutu-2, taken by Chang’e 4, just after deployment.

Compared with the missions to Mars and the asteroids, a Moon mission has the advantage that the destination is ~ 384.000 km away from Earth, communication signals take only a bit more than one second. However, for a spacecraft on the far side of the Moon, there is a problem, the Moon itself will block signals to Earth!

China has found an elegant solution for this problem: a separate satellite has been launched, the Queqiao, a few months before the Chang’e 4 launch. This communication satellite is now in a lunar orbit and will transmit the signals of the spacecraft to Earth and vice versa.

Actually the Queqiao is not orbiting the Moon, but orbiting the L2 Lagrange point, about 60.000 km above the far side of the moon. In my blog Where does the Moon come from, I have discussed a bit the concept of Lagrange points, where the gravitational force of Moon and Earth are in balance. Too complicated to explain the details, check Wikipedia for Halo Orbits.

This infographic illustrates the Chang’e mission. The Chang’e 4 has landed in the Aitken basin, near the Moon’s South Pole. This huge impact crater is 2500 km in diameter and 13 km deep !

There is one amusing detail/mistake in this infographic. It looks like the rover has four headlights! Has the creator of the infographic assumed that you needed lights, because this is the dark side of the moon?

I will update this blog when there are new developments.

Landing on Mars

Landing a spacecraft on the planet Mars is not a piece of cake!

After several failed attempts the first successful landing took place in 1976, when two(!) spacecrafts, the Viking 1 and 2, landed safely on the surface of the Red Planet. And a Red Planet it was. Here are the first (color) pictures taken, left by the Viking 1, right by the Viking 2

The next successful landing was more than 20 years later, the Mars Pathfinder in 1997. The lander contained a small separate vehicle, a Mars rover, that could independently explore the surface. Here you see the Sojourner, after it had just rolled down from the Pathfinder. It is a tiny vehicle of 63 x 48 x 28 cm and with a mass of about 12 kg.

The next mission was the Mars Exploration Rover in 2004. Two separate missions actually, landing two rovers on Mars, the Spirit and the Opportunity. Both missions were very successful, the two rovers were planned to operate for 90 Sol’s (a Sol is a Martian solar day), but Spirit remained active until 2010 and Opportunity until June this year. Actually they are still trying to contact Opportunity, hoping it survived the huge dust storm that raged on Mars this year. Check this update for the latest info.

Here is an artist impression of the Opportunity rover. Compared with the Sojourner this is a big boy..:-) , 2.3 x 1.6 x 1.5 m, mass 180 kg. Until the loss of signal on Sol 5111 (June 10, 2018) it had traveled 45.16 km.

Four years later, in 2008, the Phoenix landed on Mars, for the first time a landing in the polar region. It confirmed the existence of water ice on Mars. Here is an artist impression of the Phoenix landing. Mass about 350 kg

In 2012 the Mars Science Laboratory (MSL) mission landed a rover on Mars, the Curiosity, which is still active at the moment. Dimensions 2.9 x 2.7 x 2.2 m. mass 900 kg.

This photo shows the difference in size. In the foreground the Sojourner, left the Opportunity and right the Curiosity.

The last successful landing took place two weeks ago, 26 November 2018, when the InSight lander touched the surface of Mars. Diameter of the lander 1.5 m (without its solar panels), mass 360 kg.

Main mission is to get more information about the interior of the planet. A seismometer will record “marsquakes” and a “drill”  designed to burrow as deep as 5 m, will measure the heat flow from the interior. Here is an artist impression of the lander with the solar panels deployed. Foreground left the seismometer, right the drill.

Here is a map of Mars with the location of the eight successful landings.

More than half of all missions failed, for example the Beagle 2 in 2003 and the Schiaparelli in 2016.  For a full report , see the Wikipedia article Mars Landing.

Why is landing on Mars so difficult and risky?

Let us look in more detail at what is called the Entry, Descent and Landing (EDL) phase of a  Mars mission. This phase starts when the spacecraft enters the atmosphere of Mars and ends about 6-7 minutes later, when it lands on the surface.

For the MSL (Curiosity) mission in 2012, NASA created a fascinating YouTube video: 7 Minutes of Terror, in which scientists and engineers explain how many things can go wrong in this phase, while they can only watch helplessly. Watch the video, it takes only 5 minutes and gives a better explanation than I can provide here…:-)

But let me try. I will concentrate on the Curiosity lander because until now it is by far the most complicated mission of all.

The atmosphere of Mars is very thin, but the spacecraft enters with a high velocity of about 20.000 km/h and would be destroyed if it was not protected by a heat shield. Here is an artist impression of the so-called aeroshell in which the Curiosity (and all other landers) is safely stowed away. It consists of a backshell and a heat shield.

Here is the aeroshell in the assembly hall. The diameter is 4.5 m. You can see the Curiosity inside the backshell. On top of the backshell is the cruise stage which controls the spacecraft during the cruise from Earth to Mars.

An exploded view of the aeroshell. From left to right the cruise stage, the backshell, the descent stage, the Curiosity rover and the heat shield.

All Mars landing missions have three parts, two of which are basically the same: 1. slowing down by atmospheric friction and  2. further speed reduction by a parachute. You need one more step, because the Martian atmosphere is so thin that a parachute can not reduce the speed to (almost) zero at ground level. One way or another, you need (retro) rocket power for the last part

When the spacecraft is a lander, the “easiest” way is to provide it with retro-rockets. After the lander detaches from the backshell, it will unfold its legs and use its rockets to land. See the picture above of the Phoenix. The InSight used the same solution. Here is a picture of the InSight landing.

Rovers have to move around, so it doesn’t make sense to burden them  with the extra weight of these rockets. That’s why for the Pathfinder, Spirit and Opportunity another solution was developed. Put the retro-rockets in the backshell, lower the rover on a tether connected to the backshell,  protect it with airbags(!), use the rockets until almost zero speed, then drop the rover. Here is a collage of what it would look like for a Martian observer. Left, the airbags are already inflated, the rover is still hanging under the backshell, which is retro-firing. Middle, the rover has touched the surface but is still bouncing many times, before it comes to rest (right). Then the airbags will deflate and the rover is ready for action. Here is an animation of the landing of the Spirit rover.

The Curiosity is too heavy and voluminous for this airbag technique, so a spectacular new (and expensive) solution was developed. A sky crane!

Here is  a schematic view of the EDL process for the Curiosity. The first phase, atmospheric braking, looks normal, but there is a difference. Before the aeroshell enters the atmosphere at an altitude of 125 km, with a velocity of 20.000 km/h,  some mass is ejected one sided (“Cruise Balance Device Separation”). The resulting “unbalance” has as effect that the aeroshell will not move ballistically (like a projectile) but can be “steered” a bit through the atmosphere. The Martian atmosphere has turbulence,  storms, pressure differences etc, affecting the trajectory of the aeroshell, resulting in a considerable uncertainty in the final landing location.  The “hypersonic aero-maneuvering” reduces this uncertainty, important for Curiosity which had to land close to the rim of  the Gale crater.

At an altitude of 10 km from the ground, when the velocity is about 1500 km/h, a huge parachute (diameter 17 m!) is deployed, slowing down the aeroshell further. The heat shield is ejected 20 seconds later. From that moment,  using radar, the exact altitude can be measured, and the precise time when the descent stage & rover have to detach from the backshell. The descent stage starts firing the retro-rockets, first to move horizontally away from the backshell and the parachute. Meanwhile the rover is lowered 7.5 m  on cables, it deploys its wheels, while still connected through an “umbilical cord with the descent stage. Here is an artist impression.

                                                                                                                                             As soon as the rover touches the ground, the connecting cables are cut and the descent stage will fly up and away, to crash a few hundred meters from the rover

Curiosity has landed!                                                                                                                                                                                                                                                       All this  (and numerous details I have skipped) must happen  in less than 7 minutes. Seven minutes of terror, because everything is automatic. If something goes wrong, nobody can do anything. Besides, the radio signals back to Earth take about 14 minutes, so, when Mission Control gets the message that the spacecraft has entered the atmosphere, it has actually already landed (or crashed….) Here is an animation of the Curiosity landing. Spectacular.

Compared with the Curiosity mission, the landing of InSight was a lot simpler, basically the same as the Phoenix in 2008. The mission of InSight is to study the interior of Mars, the precise landing location is less important, as long as the surface is flat. Therefore no “guided entry” through the atmosphere was needed. The InSight is also much lighter (360 kg)  than the Curiosity (900 kg), so it was decided to provide the lander itself with rockets.

Although the EDL phase for the InSight was 6 minutes,  the catchy description “7 Minutes of Terror” was again used in the media  for this mission…:-) The BBC:    Nasa’s Mars InSight mission heads for ‘7 minutes of terror’

Of course it is still a major technological achievement! NASA published a very good explanation of InSight’s EDL phase:  InSight landing on Mars .

Here are three pictures taken by the InSight. The lander has two cameras, the Instrument Context Camera is a fisheye camera, mounted underneath the lander deck. In the first picture (left), taken a few minutes after landing, the lens is still protected by a transparent cover, because of the dust whirled up by the rockets. In the right picture the cover has been removed. and as you can see, still a lot of dust has managed to crawl under the cover and stick to the lens. Unfortunate, although the images will still be usable.

The second camera is mounted on a robotic arm, Here is a superb picture taken by this camera. The scientist are very happy with the sandy, rock-free location. The reddish box is the seismometer which later will be deployed after the best location has been determined.

The latest news about the InSight mission can be found here

 

Hayabusa2

In 2014 I have published several posts about Rosetta, the spacecraft that has explored the comet 67P. Click here for my reports. I am very interested in these Close Encounters between spacecraft and celestial bodies. Here is a new one, the Japanese Hayabusa mission. Actually there are two Hayabusa spacecrafts, the first one was launched in 2003, the second one in 2014.

Their mission was basically the same: Fly to an asteroid,  land on it, collect some asteroid material, then fly back to Earth to deliver the collected material.  An ambitious project!

Hayabusa was the first spacecraft ever that has landed on an asteroid and returned to earth with some asteroid material. Not as much as was hoped for, because the mission encountered quite a few technical problems. Therefore a second, improved Hayabusa2 spacecraft, was designed and launched on 3 December 2014.

Here is an artist impression of the Hayabusa2. The boxlike spacecraft has dimensions of 1 x 1.6 x 1.25 m and a mass of 609 kg

Destination? A tiny asteroid, 1999 JU3.. In an earlier post I have explained the complicated naming of the minor planets. The J stands for the first half of May, U stands for 20 and the subscript 3 means 3×25. So this asteroid was the 95th minor planet, discovered in the first half of May 1999. This provisional name is replaced by a number and sometimes a name, in this case 162173 Ryugu. It is the 162173th minor planet and the name has been suggested by JAXA, the Japanese counterpart of NASA.

Here is the route followed by Hayabusa2 to Ryugu.The Earth orbit in blue, Ryugu in green and the Hayabusa2 in purple.

It reached the asteroid, 3.5 year after the launch,  on 27 June 2018, . One day earlier it took this picture of Ryugu, from a distance of about 40 km

Properties of Ryugu:  not really spherical, diamond-shaped, a diameter of ~ 900 m and a rotation period  of 7.6 hours. The gravitation at its surface is about 80.000 times smaller than on Earth!

Until December 2019 Hayabusa2 will stay near Ryugu, at a distance of 20 km (HP, home position), where the gravitational attraction of the asteroid is almost nothing.  From there it will investigate the properties of the asteroid and several times it will descend for a short time to the asteroid.

On 20 September the spacecraft started a slow, controlled descent and one day later, 55 m above the surface of Ryugu, it dropped two Minerva rovers. While they were falling down to the surface, Hayabusa2 ascended to HP. Both rovers are working correctly, a huge relief for the scientist,  They are really tiny, diameter 18cm, height 7 cm, mass 1.1 kg Here is an artist impression.

Both rovers have multiple cameras and temperature sensors on board They can move around by “hopping” and do this autonomously! Wheels like for example the Mars rover has, would not work in this low gravity world.  One hop can take 15 minutes and move the rover horizontally ~15 m.

This is a picture of the Ryugu surface, taken by  one of the rovers.The scientists are surprised that the surface is so rough.

On 3 October, the spacecraft descended again to Ryugu, to drop the MASCOT lander, developed by the German and French space agencies. A bit larger and heavier, size of a shoebox, mass ~10 kg. Contains cameras and various scientific instruments. No solar cells like the two rovers, but battery operated, able to provide power during 16 hours. Also able to hop, like the rovers.

This is an artist impression of the MASCOT, leaving its container in Hayabusa2.

During the descent, Hayabusa2 was able to follow the lander. The yellow line is the actual path, the blue line is the projection on Ryugu’s surface. The times are given as “hhmmss”. After it hits the surface, it bounced several times. During the last part (straight blue line),no pictures were taken. The location 02:14:04 is the final landing place. The separate location 00:55:09 +1 is taken one day later and proves that MASCOT has managed to hop. The shadow is from Hayabusa2

Here are two images taken by MASCOT itself. Left while descending to the surface and yes, that is its own shadow top right. Right after landing, again showing a very rough surface.

After the successful landing, MASCOT started to use its scientific instruments (spectrometer, magnetometer and radiometer) and sent the data back to Hayabusa2 within the limited timespan of 16 hours. Actually the batteries lasted one hour more, a bonus. It hopped two times.

Until now the mission has been very successful: two rovers and one lander have touched an asteroid for the first time in history!

What will be next? The main mission is to collect material from Ryugu and bring it back to Earth. How to do that? Here is a schematic view of Hayabusa2. Notice the .Sampler Horn at the bottom

This is the procedure: the Hayabusa2 will descend very slowly to the asteroid until the horn touches the surface. Then a small (5g) bullet will be fired inside the horn, hit the surface at high speed and surface particles will fly up and be collected at the top of the horn. Hopefully at least 0.1 gram, maximum 10 gram. This will be done at two different locations.

The third and last one is quite spectacular, an attempt to collect material below the surface. Here is another view of the bottom of the spacecraft. Next to the horn you see the Small Carry-on Impactor.

It is an explosive device, meant to create a crater in Ryugu, so that Hayabusa2 can collect the debris. Here is how it works . The explosive will deform the copper shield (2.5 kg) into a projectile, that will hit the surface at a speed of 2 km/s, creating a crater with a diameter of several meters

By the way,  this is where the idea may have come from…:-)

The explosion must of course not damage Hayabusa2 itself! The  scientists have found this spectacular solution:

  1. Hayabusa2 approaches the surface of Ryugu.
  2. It releases the bomb and also a camera.
  3. Then it moves up and sideward to hide itself behind the asteroid!
  4. The bomb explodes and creates a crater.
  5. The camera takes images and sends them to Hayabusa2.
  6. Hayabusa2 appears again and descends above the crater.
  7. The horn will collect debris of the explosion

Here is an artist impression, where Hayabusa2 is descending above the newly formed crater.

The first touchdown of the spacecraft itself was planned for end October, but it has been postponed until January 2019.

Why?

Because the surface of Ryugu is much rougher than expected!

The horn of Hayabusa2 extends about 1 m, therefore the touchdown area should not have rocks higher than 50 cm. The touchdown area must also have a diameter of at least 100 m because of navigational accuracy.

Such a location could not be found on Ryugu!. Below is the one finally chosen (red circle) free of rocks, but ONLY 20 m in diameter!

There is also some good news. The earlier launching of the rovers and the MASCOT showed that navigation (with laser range finders) could be done more accurately (within 10 m), at least until the altitude of 50 m above the surface.

In the next weeks, two rehearsals will be performed, going lower, to find out whether tis accuracy can be maintained until touchdown.

The first real touchdown is now planned for January next year. There is enough time because Hayabusa2 will stay at Ryugu until December 2019.

All this is happening at about 300 million km away from Earth. Amazing. Keep in mind that communication between Earth and the spacecraft takes about 15 minutes, one way!

The German Space Agency has published a very instructive YouTube video, illustrating what I have tried to explain in this blog. Not only about the MASCOT lander as the title suggests.  Worth viewing more than one time!

If more news becomes available I will write an update

 

New Horizons

The first time I wrote about the New Horizons spacecraft was in a February 2015 post: Close Encounters. Launched in 2006, its primary destination was Pluto.  During the long voyage it had gone into hibernation (to save energy) and now it had woken up successfully to prepare for the flyby of Pluto in July.

To give you an impression of the size of the spacecraft, this picture is taken in 2005 during preparation for the launch.

Note the black “tube” to the left, it is the RTG, the power source for the spacecraft.

Solar panels can not be used because of the large distance to the Sun, instead radioactive plutonium is used.

The heat of the radioactive decay is  converted into electricity by thermocouples.

My second post was titled Close encounter with Pluto and published July 2015, a few days after the successful flyby. Here is a picture of Pluto, in high resolution, taken by New Horizons. Although the flyby took only minutes, the transmission of all photos taken, took more than a year, because of the slow bandwidth. Analysis is still going on.

In that post I wrote that New Horizons would try to visit another member of the Kuiper Belt before it left the Solar System. Soon after the Pluto flyby, in August 2015,  it was decided that (486958) 2014 MU69 would be the next destination.

What a name ..:-). Let me explain. The Kuiper Belt is located outside Neptune and contains trillions of objects, remnants of the early solar system. Pluto, once seen as the ninth planet, is now seen as a Kuiper Belt object. The Minor Planet Center keeps track of all the observed Kuiper Belt objects and the present count is 779736 !

The target of New Horizons is minor planet no 486958, discovered by the Hubble Space Telescope in 2014.

In this image (taken by the Hubble telescope)  you see the object (surrounded by a green circle) at 10 minute intervals

The code  MU69  tells in a complicated way that the object was the 1745th Kuiper Belt object, discovered in the second half of June! Curious about the code?  Have a look at the Wikipedia item about Minor Planet naming.

 

After a public voting campaign, NASA announced a few months ago that 2014 MU69 would get the nickname Ultima Thule. In classical and medieval literature Ultima Thule got the meaning of any distant place located beyond the “borders of the known world”

First estimate of Ultima Thule’s size, based on distance and brightness, was about 30 km. After it was chosen as the next target of New Horizons, of course many more observations have been made. How to get more information about an object of ~ 30 km, at a distance of more than 6 billion km?

Well, it can happen that Ultima Thule passes in front of a background star! In that case it will block for a short while the light of this star. This is called an occultation. Last year Ultima Thule occulted three different stars in June and July. Such an occultation can only be seen from specific locations on Earth (similar to a solar eclipse).  Here are the three predicted occultation paths.

On 3 June 2017, the NASA scientists tried to observe the “shadow” of Ultima Thule from Argentina and South Africa, but detected nothing. It turned out later that the predicted occultation path was not accurate enough, so the telescopes had been placed in the wrong location..

The second occultation took place over the ocean, therefore the airborne telescope SOFIA was used, flying along the predicted occultation path.

Main purpose was to check for hazardous material around Ultima Thule, which could endanger the fly-bye of New Horizons.

First they thought that they had missed the shadow, but later analysis showed that there had been a short dip from the central shadow

The third attempt was very successful. 25 telescopes were placed along the occultation path in South Argentina and five of them observed the dip.

Here is an example. It is an animated gif, time between the frames is 0.2 seconds.

Watch the star in the centre and notice how it “disappears” for a short while!

Careful analysis of the “dip” gives a lot more information. Ultima Thule might be actually a contact binary, with a very elongated shape.

More information about this amazing scientific exploration can be found in this  NY Times article.

Here is an artist impression of Ultima Thule. The Sun is not more than a very bright star, you can see how New Horizons is approaching… 🙂   To the  left you see a “moonlet” orbiting Ultima Thule, for a while the scientists thought there could be one, but it is now disputed.

On New Year’s Day 2019 at 05:33 UTC, if everything goes well, New Horizons will pass Ultima Thule within about 3500 km.

New Horizons has woken up from its hibernation last month and is healthy. The coming months preparations will be made for the encounter.

It will be exciting to see how Ultima Thule looks in the real. But it will take time to transmit pictures back to Earth.  It takes almost six hours for data to bridge the distance between New Horizons and Earth!

An update will follow later.

‘Oumuamua

The Haleakala volcano is located on the island of Maui, the second-largest island of Hawaii. On the top of this extinct volcano, at an altitude of 3055 m, an astronomical observatory has been built. One of the telescopes in this observatory is the Pan-STARRS telescope, with  a 1.8 m diameter mirror and equipped with the largest digital camera ever built, recording almost 1.4 billion pixels per image

The function of this telescope is to scan the sky, looking for moving astronomical objects, like comets and asteroids. The idea is simple, you take two pictures of a part of the sky, at different times and compare them.

In 1930 the planet Pluto has been discovered this way. Here are the original photographs, taken 6 days apart, the arrows point to Pluto. In those days the astronomer used a gadget, called a blink comparator, which rapidly switched from viewing one photograph to viewing the other. The moving object would stand out by “blinking”.

Nowadays computers can do this much better than humans, and Pan-STARRS is connected to a sophisticated computer system, that not only analyses the images, but also communicates with other observatories all over the world, when moving objects are found.

The interest in these objects is not only scientific. Pan-STARRS is taking part in the NEO Search Program. NEO stands for Near Earth Object, and NEO‘s are objects, mostly asteroids, that could collide with Earth in the future. Readers who have been following my blog from the start, may remember my posts about the asteroid Apophis, published in 2010(!). In 2013 Pan-STARRS had already discovered 10.000 NEO’s

On 19 October 2017 a new moving object was discovered by Pan-STARRS.  At first it was assumed to be a comet, and named C/2017 U1   but as it had no characteristic comet tail, it was reclassified one week later as an asteroid : A/2017 U1


A short intermezzo about the classification of comets. The first letter describes the kind of object, P for a periodic comet, C for a comet with unknown period and A for an object that was first classified as a comet but is actually an asteroid. There are a few more categories. The letter is followed by the year of discovery and by a letter that indicates the “half-month” of discovery. A for the first half of January, B for the second half, C for the first half of February, etc. The letter I is not used, so the U means that the object was discovered in the second half of October. It is here followed by the number 1, because it was the first discovery in that half-month.


Further observation of this asteroid, by many other observatories, showed that it came from OUTSIDE our solar system!

A few years ago I have published a post about NEO’s,  Visitors from Outer Space, but Outer Space stands there for the Kuiper Belt and the Oort cloud, both still belonging to our solar system.

So this was an EXTRAORDINARY event, the first observation of an object that came from another star! On 6 November 2017, less than three weeks after its discovery, it was reclassified again, as 1I/2017 U1 , where a new category was introduced, I, standing for Interstellar object. The number 1 in front of the I was added, because it was the first occurrence of this new category. And it was given a proper name: ʻOumuamua, which in the Hawaiian language means “a messenger from afar arriving first“. The symbol ʻ in front of the name is not a typo, but a ʻokina, a glottal stop.

How do the astronomers know that it comes from outside our solar system? By its speed and its orbit! Here is an animated gif of ʻOumuamua’s orbit.

The orbit is hyperbolic ! From far away it approached the solar system with a velocity of ~26 km/s. Attracted by the Sun, its velocity increased to ~88 km/s at perihelion, on 9 September 2017. When it was discovered by Pan-STARRS, 40 days later, it was already on its way out.

Here is another sketch of ʻOumuamua’s orbit, with dates. Try to view it “3-dimensional”, the orbital plane of ʻOumuamua is tilted with respect to the ecliptic (the orbital plane of the planets).

Is there anything more that we know about this visitor from outer space? For example from which star it started and how long it is underway?  It arrived roughly from the direction of the star Vega, 25 lightyear away. In that case, with its velocity it would have taken ~ 600.000 year to reach our solar system. But Vega was not in the same location, that long ago. We just don’t know, ʻOumuamua could have left its star system billions of years ago.

Surprisingly we know a bit more about its shape, its size and its color! The color is dark reddish and the size is roughly 200 x 30 m.  A kind of gigantic cigar…:-) Here is an artist impression

You may wonder how anything can be said about the shape, as the image of ʻOumuamua is only a single pixel in even the strongest telescopes! The answer is that the asteroid is “tumbling” with a period of ~ 8 hours. Therefore the amount of light it reflects varies.

Here are the measurements done by several telescopes, with a theoretical fit, assuming a 1:10 ratio between length and width  Click to enlarge.

Of course there are people who are wondering if it could be a spaceship…:-). In that case it would probably be out of control or abandoned, because of the tumbling. Anyway, both SETI and Breakthrough have been listening for any signals coming from ʻOumuamua. Without results.

For this blog I have used the very informative Wikipedia article about  ʻOumuamua and other Internet sources.

Physics Nobel Prize 2017

Last month  the Nobel Prize for Physics has been awarded to three American physicists for their ” decisive contributions to the LIGO detector and the observation of gravitational waves”

Here they are, from left to right Rainer Weiss (85), Barry Barish (81), Kip Thorne (77) .

All are retired professors and quite old, not unusual for Nobel Prize winners…:-; More unusual is that this Nobel Prize has been awarded for the observation of gravitational waves in September 2015, only two years ago! The time between a discovery and the Nobel Prize is often 10-20 years and tends to increase

In this case the physics community was pretty sure that the Nobel Prize would go to  LIGO, the Laser Interferometer Gravitational-Wave Observatory, where the gravitational waves were observed. Problem is that a Nobel Prize (with the exception of the Peace Prize) can not be awarded to an organisation but only to a maximum of three individuals (and never posthumously). And the article in Physical Review Letters, where the discovery was published in February 2016, has more than 1000(!) authors. Here is the beginning of the author list

In this blog I will explain why these three people were selected. But first I must tell a bit more about gravitational waves, and why physicists are so excited that they have been observed.

In 1687 Newton publishes his  masterwork “Principia” in which he presents the three laws of motion  and the universal law of gravitation.

Motion takes place in 3-dimensional space as a function of time. Both space and time are absolute concepts, independent of each other.

Newtonian mechanics works extremely well, but there is one disturbing fact, the speed of light c in vacuum turns out to be always the same, no matter how fast the light source is moving itself. Einstein  “solved” the problem in 1905 by accepting the constancy of c as a fact, which resulted in  his Theory of Special Relativity (TSR)

But it came at a price! Space and time are no longer absolute and independent in this theory, together the three dimensions of space and the single dimension of time form a 4-dimensional continuum, called spacetime .

Gravitation doesn’t play a role in the TSR, but in 1916  Einstein publishes his Theory of General  Relativity (TGR). In this theory gravitation is described as a curvature of  spacetime. A massive object like the Sun curves the spacetime in its surroundings and a planet like Earth just “follows” this curvature.

A consequence of this theory is that even light would follow this curved spacetime and will be deflected when it passes close to the Sun. This prediction was successfully confirmed only a few years later. During a solar eclipse the stars near the Sun became visible and their position was shifted in complete agreement with the TGR. It was front page news and made Einstein world famous.

 

Another prediction of the TGR was that (accelerated) motion of massive objects could produce waves and ripples in this fabric of spacetime. Mind you, in spacetime itself ! However, these waves and ripples were estimated to be very small, maybe only measurable if  those objects were extremely massive.

For example, two black holes or neutron stars, orbiting each other.

Here is an artist impression of the gravitational waves caused by two orbiting black holes. I have hesitated to include this image, because I find it very confusing, suggesting that the cells of the spacetime fabric are moving up and down, whereas the cells themselves are changing shape, stretching and contracting. But the image comes from LIGO, so who am I…:-)?

After this long(?) introduction it is time to go back to LIGO and the three Nobel Prize winners.

LIGO has a long and complicated history, starting in the 1960!  Here are some important dates. The names of the three Nobel Prize winners in blue.
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In 1968, almost 50 (!) years ago, Kip Thorne (Caltech) did calculations about the gravitational waves of black holes. Which, by the way, had not yet been discovered at that time, but their existence followed from the TGR! He came to the conclusion that detection should be possible. Also in the 1960s, Rainer Weis (MIT) proposed to use interferometry to detect the incredibly small variations in the fabric of spacetime. See below for more about interferometry.

In 1980, under pressure of the American National Science Foundation (NSF) , MIT and Caltech joined forces in the LIGO project. But progress was slow and funding not easy.

In 1994Barry Barish (Caltech) was appointed director of the project. He was a good organiser, proposed to build the LIGO detector in two phases. This proposal was approved by NSF and got a budget of  USD 395 million,  the largest project in NSF history!

In 2002, the first phase of LIGO became operational, but no gravitational waves were detected.

In 2004, funding and groundwork started for the second phase, “Enhanced LIGO”, four times more sensitive than the first phase.

In September 2015, after a 5 year overhaul of USD 200 million was completed, Enhanced Ligo started operating.

Within days, on 14 September at 9:50:45 UTC,  Enhanced LIGO detected gravitational waves for the first time in history.
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So, what is an interferometer? Here is a sketch of the LIGO interferometer

And who could better explain how it works than Rainer Weis himself?

What may not be fully clear from the video is the huge scale of this LIGO project.

Two “identical” interferometers have been built in the US, about 3000 km apart

Here is an aerial view of  the Hanford interferometer, each of the arms is 4 km long!

Both interferometers can be seen easily on Google Earth. Left Hanford, right Livingston.

As Weis explained, gravitational waves cause small differences in the length of the arms. Very, very small. In the order of  10-19 m, that is about 1/10.000 part of the size of a proton. Read that again and again, I still find it difficult to believe..:-)

The sensitivity must be about 1/10.000 part of the size of a proton.

New technology had to be developed to reach this sensitivity. Ultra-high vacuum, very precise mirrors, extremely stable lasers. Noise reduction (thru seismic vibrations, a passing truck, etc) is the main problem. That is also the main reason that two interferometers were built. Accidental noise should be different in both detectors, but a gravitational wave should reach both (with a slight time difference, because of the distance between the two detectors).

Critical is the suspension of the mirrors. They must be absolutely stable. Here two images of the damping and suspension systems. Click here for details

What kind of signal do we actually expect? Let’s concentrate on orbiting back holes (it is called a binary), like Thorne did. As shown in the earlier image, they produce gravitational waves, but those are way too small to be detected. However, the binary will loose energy sending out these waves, as a result over time the two black holes will get closer and closer. Until they come so close that they will merge into one larger black hole, a cataclysmic process that may take less than a second! It is during this phase that the gravitational waves are much stronger and might be detectable.

Here is a computer simulation of the merger of two black holes. The simualtion has been SLOWED down about 100 times, in reality the merger occurs in a split second. The “moving” background stars are a result of the extreme distortion of spacetime.

Click here to see the gravitational waves, sent out during the merger.

You will notice that before merging the two black holes spin faster and faster, distorting the fabric of spacetime more and more. It is a bit similar to a bird chirp: increasing frequency and loudness.  After they merge into one, no more gravitational waves.

So, what happened on 14 September 2015? The two interferometers were to start the first research run on 18 September and were already in fully operational “engineering mode”, when at 9:50:45 UTC both detected  the typical “chirp” signal.  For testing purposes sometimes “fake” signals were injected, to test the alertness of the system and the scientists. It took a few hours before it became clear that this was a real signal and not a test!

Here is the “Nobel Prize winning” signal. The red graph is from Hanford, the blue one from Livingston (the Hanford signal is also shown, inverted and shifted in time)  Notice the time scale, the whole merger takes place in a few tenths of a second!

The lower two graphs show a fit to the data, using Numerical Relativity. It is surprising how much information can be extracted from these two graphs. Here is a (partial) result

Two black holes, with a mass of 35 and 30 M☉. (solar mass) , at a distance of about 1.4 billion lightyear away from Earth, merged into a single black hole of 62 M☉. .

The mass difference of 3 M , was radiated during the merger as gravitational waves. That is an awful lot of energy!  The estimated peak emission rate was greater than the  combined power of  all light radiated by all the stars in the observable universe! If you don’t believe me, click here.

This first event has been named GW150914. GW stands for Gravitational Wave and is followed by the detection date 14-9-2015. In the past two years more gravitational waves have been detected, here is a list

If you look at the location, you see that in the first five events the location of the binary is not well-defined. The reason is that you need more detectors to determine the location accurately, two is not enough.

The sixth event, GW170814 was not only detected by LIGO, but also by Virgo , the European counterpart of LIGO. This interferometer is located near Pisa in Italy. Same setup as LIGO, slightly smaller arms (3 km)

Virgo was also designed in two phases. The first phase did not detect gravitational waves. In 2106 Advanced Virgo became operational and is now cooperating with LIGO.  Another interferometer will be built in India: INDIGO .

The last event, detected until now, GW170817 (about three months ago), is an interesting one, because it is not a merger of black holes! For the first time a merger of two orbiting neutron stars has been observed. The masses of the two stars are comparable with the Sun and the binary is closer to Earth, although still a respectable 130 million lightyear!  It is not sure if the merger resulted in a neutron star or a black hole. But anyway, a merger of neutron stars should result in visible light coming from the debris after the merger.

Because of the detection with three interferometers, it was possible to narrow the region of space where the gravitational waves came from.  The location predicted by LIGO/Virgo was still large, about 150 times the area of a full moon. Within hours after detection, alerts were sent to astronomers all over the world and a massive search started.

A few hours later the Swope telescope in Chili reported they had found  the source in galaxy NGC 4993  , 140 million lightyear away. This was soon confirmed by other observatories.

Here is an image of this elliptical galaxy. The inset shows the light coming from the merger, getting weaker and weaker, as expected.

More interesting discoveries can be expected in the future, this is just the beginning.

When you want to learn more about this fascinating new field of astronomy, you should read the book Ripples in Spacetime, written by Govert Schilling