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.
In this blog I will give updates about three space exploration missions described in earlier posts and report about two new ones.
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.
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.
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 😉
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… 🙂 )
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 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.
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
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:
Hayabusa2 approaches the surface of Ryugu.
It releases the bomb and also a camera.
Then it moves up and sideward to hide itself behind the asteroid!
The bomb explodes and creates a crater.
The camera takes images and sends them to Hayabusa2.
Hayabusa2 appears again and descends above the crater.
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.
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
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!
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!
So this was an EXTRAORDINARYevent, 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.
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.
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. __________________________________________________________________
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 1994, Barry 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. __________________________________________________________________
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
Are you using Whatsapp and did you recently receive this picture? Getting excited already, that in a few weeks time you will observe a unique event?
Sorry to disappoint you, but this is complete nonsense. Yes, on 21 August 2017 there will be a total solar eclipse, and to watch it is an experience of a lifetime. But solar eclipses are common, almost every year there will be a solar eclipse visible, somewhere on Earth..:-)
Here is a list of solar eclipses between 2011 and 2020. In the third column the type of eclipse is given. Twenty four eclipses in total, five of them total. The last column gives the geographic region where the eclipse will be visible.
I do not want this blog to be very technical, but some explanation may be useful..:-)
A solar eclipse occurs when the moon passes between the sun and the earth.
The moon orbits the earth in about 29 days, so you would expect a solar eclipse roughly every month. But the orbital plane of the moon is tilted 5 degrees, therefore the shadow of the moon will not touch the earth every month. Also, because of the (big) size of the sun, the shadow of the moon (the white lines) just reaches a small part of the earth. The pink lines mark the region where the moon blocks the sun only partially.
Another effect is that the orbit of the moon is slightly elliptical, so the distance of the moon to the earth is not always the same. If the moon passes between the sun and earth while it is farther away from the earth, it can not block the sun completely, resulting in an “annular” eclipse.
Let us look in a bit more detail at the 21 August eclipse. The blue band is where you can see the total eclipse. Weather permitting of course…:-) The light blue lines parallel to the blue band indicate the regions where you have a 75%, 50% and 25% partial eclipse.
Is there anything special about this eclipse? Yes..:-) It will only be visible from the Unites States of America and no other country! AMERICA FIRST…:-) Probably Trump will twitter one of these days that it is one of the successes of his administration…;-)
Of course there is a lot of interest in the USA for this Great American Eclipse . Here are a few advertisements, taken from the Internet.
But also for the USA it is not a unique event. The last total eclipse, visible in mainland USA, was on 26 February 1979 and the next one will be on 8 April 2024.
Total eclipses are spectacular. It gets dark, and the solar corona becomes visible. A reason for many people to travel to a region where the total eclipse can be watched.
Actually I was one of them, 8 years ago!
Friends told us about a total eclipse, visible in China on 22 July 2009. Here it is
This post is about the planet Jupiter and the spacecraft Juno, launched in August 2011 and orbiting Jupiter since July 2016. The image shows both the planet and the spacecraft.
But we will start with some Roman (Greek) mythology. Jupiter (Zeus) was the king of the gods and Juno (Hera) his wife. Jupiter was an promiscuous god with numerous extramarital affairs and Juno was a jealous spouse, always keeping a eye on her adulterous husband. Here are a few of his affairs
He lusted for Io, and transformed the girl into a cow, to hide her from his wife. In vain, Juno asked him to give her the cow as a present.
He abducted Europa, disguised as a bull. King Minos of Crete was one of their children
He fell in love with the nymph Callisto and took the shape of virgin goddess(!) Artemis to seduce her.
He was so enchanted of Ganymede, that, in the shape of a raven, he took the beautiful boy(!) to Mount Olympos.
You will understand that as schoolboys we were always happy when our Latin and Greek teachers told us about these myths…:-)
Back to astronomy. Jupiter is the largest planet in our solar system. The planet is so big that all the other planets would fit in it. It is the second-brightest planet (after Venus) in the night sky.
In 1610, Galileo discovered that Jupiter has four moons. In the image you can see their size, compared to Jupiter. They look small beside the planet, but they are actually big. The largest one, Ganymede, is bigger than the planet Mercury!
The four moons were named after the four lovers of Jupiter named above! Below you see a (resized) image of each moon and a painting with Jupiter in action.
Callisto seduced by Jupiter disguised as Artemis. Boucher (1759)
The abuction of Europa Jean François de Troy (1716)
Jupiter and Io Paris Bordone (~1550)
The abduction of Ganymede Eustache Le Sueur (~1650)
Since Galileo observed the four moons, many more (smaller ones) have been discovered. At the moment 67 moons have been observed, of which 53 have been named, often after Jupiter’s girlfriends and boyfriends…:-) Here is the complete list of Jupter’s moons
It may now be clear why the spacecraft has been named Juno 🙂 After the launch of the spacecraft, NASA published a mission statement in which they explained the name of the spacecraft:
“The god Jupiter drew a veil of clouds around himself to hide his mischief, and his wife, the goddess Juno, was able to peer through the clouds and reveal Jupiter’s true nature.”
Actually the mission of Juno is to explore Jupiter and not his moons…:-) Much is still unknown about this gas giant. Does it have a solid core? Does its atmosphere contain water? An important part of the mission will be the study of Jupiter’s gravitational and magnetic fields.
So, let us follow Juno on her exploration of Jupiter. It took her five years to reach Jupiter. Why so long? Here is the reason:
To give the spacecraft enough speed at launch to reach Jupiter would cost too much energy. Therefore it is first launched in an (elliptical) orbit around the sun.
The Deep Space Maneuvers one year later will bring it back very close to Earth, which will give it a gravitational slingshot. See my Rosetta blog for an explanation.
As a result the orbit becomes a hyperbole, at the right moment crossing the orbit of Jupiter, where it will be captured by the planet.
Here is a fascinating animation of the whole process.
Jupiter has to be approached carefully because of its intense radiation belts. The magnetic field of a planet traps charged particles like electrons and protons in a doughnut-shaped region around the planet. Earth has these radiation belts, they are called the Van Allen Belts. For Jupiter they are many thousand times stronger and can seriously damage the spacecraft.
To protect the instruments of Juno, the most sensitive ones have been placed in a titanium container with 1 cm thick walls and a weight of 18 kg.
Here is an image of the spacecraft during assembly. The Radiation Vault is the brown box on top of the spacecraft.
Note the size of the human!
To minimise the radiation risk, Juno has to be captured carefully in a polar orbit. Here is a YouTube animation:
The capture orbit is very elliptical with a period of ~ 54 days. The original plan was to reduce the period to 14 days, after two capture orbits (1 and 2). The first reduced orbit (3) would be a clean-up orbit, followed by 32 “science” orbits (4-36), each of them slightly shifted, so the whole surface of Jupiter would be covered.The image gives an impression of these science orbits. Mind you, during each 14 days only a few hours before and after perijove (the point of shortest distance to Jupiter) can be used for science!
However, during the second orbit, a few days before the planned Orbit Reduction Maneuver on 19 October 2016, a problem was found with some helium valves needed to operate the main engine, and a few hours before perijove, the spacecraft went into “safe mode”, because the onboard computer encountered unexpected conditions. The next two orbits were used for testing and diagnostics.
Finally, on 17 February 2017, mission control decided it was too risky to perform the Orbit Reduction Maneuver. So the spacecraft will remain in its 54 day orbit. Totally 12 science orbits will be performed until July 2018. The next perijove (orbit 7) will occur on 11 July.
It must have been quite a disappointment for the scientists, instead of new data every two weeks, they now have to wait almost eight weeks.
Are there results already? The instruments that are measuring the magnetic field of Jupiter and the composition of the Jovian atmosphere are collecting data, it seems the magnetic field is more lumpy than expected.
The most spectacular results come from the on-board camera Junocam. Here is an image of Jupiter’s south pole, not observable from Earth. Amazingly complex and turbulent.
And last week NASA published another picture, taken 19 May, just after Juno passed perijove 7. Keep in mind that these images are color enhanced! Part of the south pole region is visible. The white spots are part of the “String of Pearls”, massive counterclockwise rotating storms.
The next orbit will pass over the famous Great Red Spot, a storm on Jupiter that has lasted already for several hundred years and is so big that Earth would fit inside it. Will be interesting to see images.
At the end of the Juno mission, the spacecraft will be directed into the Jovian atmosphere, where it will be completely destroyed. This will be done to avoid any chance that material of Juno might “contaminate” one of Jupiter’s moons. If ever life forms are found on these moons, there must not be any doubt about its origin.
To end this post in a lighthearted way, the Juno has three passengers on board! Figurines, specially crafted by Lego in the shape of Jupiter (with a lightning bolt), Juno (with a magnifying glass) and Galileo (with a telescope and Jupiter in his hand)
Preparing this post, I have made extensive use of a very informative web page: Juno Mission and Trajectory Design . Very detailed and sometimes quite technical, but worth reading.
Tomorrow, 31 December 2016, just before midnight, an extra second will be added to the Universal Coordinated Time (UTC)! It is called a leap second.
Probably everybody will be familiar with the concept of a leap day . A year in the international calendar has 365 days, but the solar year is a bit longer, 365.25 days. To keep this calendar synchronised with the solar year, every four years an extra day (29 February) is added to the calendar, a leap day. 2016 was a leap year, the next one will be 2020.
The Chinese calendar is based on the motion of the Moon, orbiting the Earth with a period of 29.53 days. A (lunar) year is 12 months = 12 × 29.53 = 354.36 days, about 11 days shorter than the solar year. To keep this calendar synchronised with te solar year, every two/three years an extra month is added, a leap month. Next year will be a leap year in the Chinese calendar, it will have 13 months with one of the months duplicated. Not always the same month, this time the 6th month. More detailed information about calendars can be found on my website
For those not familiar with UTC, it is the primary time standard by which the world regulates clocks and time. It is basically the solar time at 0° longitude, with the solar day as fundamental unit. The 0° meridian passes through Greenwich, therefore UTC is sometimes called Greenwich Mean Time (GMT). The world has been divided into 24 time zones, they are defined as UTC plus or minus a number of hours. For example Malaysian time is UTC + 8.
So, the UTC is based on the (solar) day and a day is 24 x 60 x 60 = 86400 seconds, right? Why do we need to add a leap second? The answer is simple, but may surprise you.
A (solar) day is not exactly 86400 seconds!
Here is a graph of the “extra” length of day over the last few decades. Click to enlarge and see more details
It is only a few milliseconds every day, but it accumulates! Therefore it has been decided, in 1972, to add an extra second to UTC, when this accumulated deviation gets more than 0.9 second. The red graph shows when leap seconds were inserted. As you see, the deviation from 85440 seconds is quite irregular and actually not predictable. That’s why the leap seconds are announced only 6 months in advance.
Why are the deviations always positive? That has an interesting, physical, reason. It is because of the moon! The moon is responsible for the tides, causing friction! This friction slows down the rotation of the Earth! It is a small but real effect, the solar day increases about 1.4–1.7 milliseconds per century. There is geological evidence that about 500 million year ago, the length of the day was shorter, ~ 22 hours.
The leap second will be added to UTC, 31 December at midnight. 23:59.59 will not be followed by 00.00.00 but first by 23.59.60
In Malaysia (UTC + 8) the leap second will be added on 1 January. 07:59:59 should not be followed by 08:00:00 but first by 07:59:60.
Computer guys are not happy with an insertion of an extra second. It may cause computer failure. The Google engineers will just slow down the system clock slightly, from 10 hours before, until 10 hours after midnight, resulting in 1 second extra…:-) Technical details here
Time reckoning is a complicated topic. I have simplified it here…:-)