Category Archives: Science

DART and Hera

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Four years ago, on 23 November 2021, I published a post titled “The DART Mission,” about NASA’s attempt to crash a spacecraft into a small asteroid in an effort to divert its orbit. The launch would take place the next day, and the crash was planned on 23 September 2022. So I ended the post with: My next update about DART will probably be in October next year.

Here is finally that update ;-). Let me start with an image from that blog. Didymos is an asteroid, a Near Earth Object (NEO) and even a Potentially Hazardous Asteroid (PHA), although there is no risk of collision with Earth in the next hundred years. A tiny moonlet Dimorphos, orbits the asteroid and was the target for the mission.

After a successful launch on 24 November 2021, DART arrived at the asteroid on 26 September 2022, about 11 million km away from Earth. How to direct DART to hit the tiny moonlet (about 150 m in diameter)? DART must do that itself with the help of its built-in camera DRACO. Four hours before reaching Dimorphos, still about 90.000 km away, DART became autonomous, using DRACO for navigation. Here is a photo taken by DRACO, 2.5 minutes before impact, the last picture where Didymos is still fully visible.

NASA collected all the pictures taken by DRACO and combined them into a time-lapse video. It shows the final 5.5 minutes, ten times faster, except for the last 6 images, which are shown in real time, every second. The “shakiness: in the beginning is a result of minor course corrections. The last image could only be transmitted partly because of the crash. A fascinating video.

The collision of DART and Dimorphos was a frontal one, so it reduced the speed of the moonlet a little but. This would cause Dimorphos to move a bit closer to Didymos with a slightly shorter period (see the first image above). Before the impact, one orbit of Dimorphos took about 12 hours. I wrote in my 2021 blog that the impact was expected to shorten the period by about 10 minutes. So it was a surprise that after the crash, the period of Dimorphos became 34 minutes shorter! In the appendix I explain how they could measure this, from Earth!

The explanation for the large reduction, was that the speed reduction of Dimorphos was not only caused by the crash of DART, but also, and even more, by the material blown away from the moonlet, causing an additional recoil.

How do we know that there was a lot of debris ejected by the crash? Because there was an eyewitness!

DART had on board a tiny spa craft, called LICIACub, which it released two weeks before reaching Dimorphos. This LICIACub had two cameras on board to take pictures of the crash and its aftermath. Here are two of the pictures. The left picture was taken 156 s after the impact, the right one after 175 s. The crash caused a lot of moonlet material to be ejected, probably leaving a crater in Dimorphos.

DART was very successful . It demonstrated that impacting asteroid could divert its course, important if ever an asteroid would be on a collision course with Earth.

n. October 2019 I published a blog Will an asteroid hit Earth?, after frightening reports of an impending asteroid collision with Earth appeared in the tabloid press. in that post I explained that the reports were sensational and not true. But catastrophic collisions have occurred in the past and may happen again in the future, so Earth must be prepared. NASA has its Planetary Defense program and so do other Space Agencies.,

In the context of this Planetary Defense, an ambitious collaboration started around 2013, between NASA and ESA. the Asteroid Impact and Deflection Assessment (AIDA) project. Two missions, DART by NASA and AIM (Asteroid Impact Mission) by ESA. AIM was to become the eyewitness, launched earlier than DART and going into orbit around Didymos, from where it could observe the impact and its aftermath.

The AIDD mission is shown below. AIM (lower right) is already in orbit around Didymos and has released two CubeSats and a Mascot lander which is hovering at the moonlet, here still called Didy-moon.

A fascinating project. But already a few years later, in 2016, ESA had to cancel the AIM mission, because Germany was unable/unwilling to contribute its portion of the funding. NASA decided to proceed with DART anyway and managed to include inro the spacecraft a CubeSat, which could act as an eyewitness. In my blog about DART, I wrote: As an European, I feel rather ashamed.

Then, in 2018, ESA came up with an alternative for AIM, called Hera. Basically, with the same mission, only reaching the asteroid in 2026, four years after the impact of DART. Here is an artist’s impression. It shows Dimorphos, with a very pronounced crater, the result of the crash. Two CubeSats are shown. No lander, but one if the CubeSats may land on the moonlet at the end of the mission.

Hera was successfully launched on 7 October 2024 and is now on its way to Didymos, where it will arrive in late 2026. In 2022 The atseroid was 11 million km away from Earth, but Hera has to travel nuch farther, abou 190 miilion km. In the video you can follow the trajectory of Hera. On12 March 2025 the spacecraft has used a gravity assist from Mars to get the right course to Didymos. In the vidoe Hera is the orange dot and Didymos the red one.

During the flyby Hera took fascinating pictures of Mars and its small moon Deinos.

When Hera arrives at Didymos, it will go into orbit around the binary asteroid. Spacecraft has landed on asteroids and crashed into them, but never gone into orbit. It needs careful navigation, much of it autonomous. Hera will study the crater formed by the impact of DART and investigate the properties of Didimos and Dimorphos. A fuill programme for the planned 6 months of the mission.

Appendix

You may wonder how astronomers discovered that Didymos had a companion, the tiny moonlet Dimorphos. Even with large telescopes, the asteroid shows as a tiny speck of (reflected) sunlight. In 2003 scientists noticed that the brightness of the speck of light varied periodically, showing tiny dips. They concluded that there had to be a companion transiting the asteroid, passing in front and at the back! They could measure the period to be 11 hours and 55 minutes, before the impact, and 34 minutes shorter after the impact.+

This image shows the effect, in an exaggerated way. The big dips are when Dimorphos passes behind the asteroid, the smaller ones when it transits before the ateroid, blocking a bit of its light.

The actual effect is so small that the scientists need advanced techniques to filter the data.

Apophis and Ramses

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Besides eight planets, our solar system has a huge number of smaller astronomical bodies, mainly asteroids, but also comets and dwarf planets. They are collectively called Minor Planets, and data about their properties are collected by the Minor Planet Center in a database. At the time of writing this blog, the monumental database contains 1,478,907 objects, with new discoveries added daily. Most objects are asteroids in the main belt between Mars and Jupiter, but there is an important subcategory, the Near-Earth Objects (NEO), that come close to Earth. Their number in the MPC database is now 40,146, also daily increasing. When asteroids in this category have orbits that cross the orbit of Earth, and are large enough to cause substantial damage in case of a collision, they are called Potentially Hazardous Asteroids (PHA). At the moment, their number is ~2500, with an estimated ~2000 not yet discovered.

This beautiful image, published by NASA in 2013, show the orbits of the ~1400 PHA’s, known at that time.

On 19 June 2004, the Pitt Peak National Observatory discovered a “new” asteroid. It got a provisional designation 2004MN4 in the MPC database. In a recent blog, I explained the coding used by MPC. The M stands for the 2nd half of June, the N for the number 13, and the 4 means 4×25. This asteroid was the 13 + 4 x 25 = 113th asteroid, discovered in the second half of June 2004.

But 2004MN4 was not an ordinary asteroid. After its orbit was calculated, it became clear that it was a NEO and even a PHA, with a small probability (2.7%) that it would hit Earth on 13 April 2029. More accurate calculations of its orbit showed that it would not hit Earth, although it would come very close, and there remained a possibility that it might hit Earth exactly 7 years later, on 13 April 2036.’ The asteroid got a permanent number in the MPC database (99942) and was given the name Apophis, the Egyptian god of the underworld, the enemy of the sun god Ra.

The possibility of a hit in 2036 remained a matter of concern, and in December 2009 I read in the Guardian about a Russian proposal to send a spacecraft to Apophis and modify its course away from Earth. The newspaper had this impressive artist’s impression of what could happen if Apophis were to hit Earth. Click on the image for a link to the Guardian article.

This was the first time I read about Apophis, and I was curious to know more. I had just started blogging, and in January 2010 I published my first post: Will the Earth be hit by Apophis in 2036? I got a few comments from readers and published a second post a few weeks later: Again Apophis, with more details and an explanation why in 2036 it would be again on 13 April.

In the following years, accurate calculations of Apophis’ orbit showed that also in 2036 the asteroid would not hit Earth, not even in the next 100 years. Actually, none of the known PHA’s will hit Earth in the next century!

But on 13 April 2029, less than 4 years from now, Apophis will pass Earth within about 30,000 km. That is closer than the orbits of the geostationary satellites. An asteroid crossing our own backyard, what a unique opportunity!

In July 2024, the European Space Agency (ESA) proposed a mission to Apophis. It got the name Ramses (Rapid Apophis Mission for Space Safety), to be launched between mid April and mid May 2028 and to arrive at Apophis in February 2029 . It would then measure properties of Apophis before, during and after the flyby. It would also deploy two so-called CubeSats, miniature spacecrafts. One of them might try to land on Apophis. Here is an artist’s impression of RAMSES, the two CubeSats and Apophis, about 30,000 km above the surface of Earth.

Preparations for the mission started in July 2024 with partial funding by ESA. In August 2025 JAXA, the Japanese Space Agency, decided to collaborate with ESA and received funding from the Japanese government. RAMSES will be launched on one of their rockets.

Would RAMSES receive full funding by the European Union? Those decisions are made by the ESA Council meeting at Ministerial level, this year held in Bremen, 27 November. The result:

The largest contributions in the history of the European Space Agency, €22.1 bn

Three missions have been approved. So It means green light for RAMSES, which now has to be built on a very tight schedule, within two and a half years! But it makes sense, because RAMSES is part of ESA’s Planetary Defense System. Apophis is not dangerous, but another asteroid might be in the future, and inthat case fast action is critical. It explains the “Rapid” in the name of the mission.

This will be the first post about RAMSES, just to celebrate that it has been funded.

Alien attack in November?

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The Sun, a UK tabloid, published on 17 August an article titled: A MYSTERY++ object tearing towards Earth at break-neck speed has raised fears that ALIENS are on their way here with these two pictures

That sounds scary, right? What is happening?. Here are the facts.

The “Mystery object” was discovered on 1 July 2025 by ATLAS (Asteroid Terrestrial-impact Last Alert System). ATLAS is a cooperation of earth-based observatories that continuously watch the sky, looking for moving astronomical objects. ATLAS started in 2015 and currently five observatories are taking part. They specialise in looking for smaller asteroids that may impact Earth and can only be detected when they are close. a last alert. Until now they have found 1241 Near-Earth asteroids, of which 110 were potentially hazardous. But also other objects were found, 106 comets and 4847 supernovae (which don’t move but change brightness)

The object found on 1 July is a comet, but it is causing huge excitement in the scientific community because of its extremely high speed. That means it comes from outside our solar system, will be slightly deflected by the Sun, and will escape again. Here is its (hyperbolic) orbit. The (animated) image comes from Wikipedia: 3I/ATLAS

The Wikipedia article contains a massive amount of information about 3I/ATLAS, a proof of the excitement caused by its discovery. Two more pictures from Wikipedia, the original discovery photo (animated gif) and a detailed photo taken by the Hubble telescope on 21 July.

The fuzziness of 3I/ATLAS in the Hubble picture is characteristic of a comet. The icy nucleus is hidden in a coma, water and dust evaporated by the solar radiation. That’s why the present estimate of its size is very inaccurate ( between 0.32 and 5.6 km). The comet will reach its perihelion (closest distance to the Sun) on 29 October and will never come closer to Earth than 209 million km (on 19 December).

Until now, three interstellar visitors have been detected: 1I/’/Oumuamua in 2017, the interstellar comet 2I/Borisov in 2019, and now 3I/ATLAS. In my blog post of February 2018, Oumuamua, I discussed in detail the first interstellar visitor. Now we have another one.

So, why the consternation in the popular press and the social media, like here or here or here. Google for 3I/ATLAS alien and you will find more links.

In my Oumuamua post, I wrote: “Of course, there are people who are wondering if it could be a spaceship”. Basically, it was one man who suggested this, Avi Loeb, an astrophysicist at Harvard University. He was widely criticised by the scientific community. He even wrote a popular science book about it: Extraterrestrial. The consensus is now that Oumuamua is just a physical object.

Avi Laub must have an obsession with alien life. Within weeks of 31/ATLAS’ discovery, he published an article, Is the Interstellar Object 3I/ATLAS Alien Technology? Here is a quote (bold by me):.

As largely a pedagogical exercise, in this paper we present additional analysis into the astrodynamics of 3I/ATLAS, and hypothesize that this object could be technological, and possibly hostile as would be expected from the ‘Dark Forest’ resolution to the ‘Fermi Paradox’

He also has a blog and wrote two posts about 3I/ATLAS, on 17 July and 5 August . And two weeks ago, he was interviewed by FOX 10 Talks. Click on the screenshot to watch the video. The interviewers are in awe that, for the first time, they have a Harvard professor in their program.

When Loeb is right about 3I/ATLAS, that it might be an alien, hostile spacecraft, what about November? Here is a possible scenario.

The spacecraft, disguised as a comet (!), reaches perihelium on 29 October. If you look at the animated GIF above, you will see that Earth is then on the other side of the Sun, so 3i/ATLAS will not be visible to us. During that period, the spacecraft will change its course and when it is visible again, it will come to attack and destroy us!

Just when I was ready to publish this post, I came across this website: Elon Musk: “It’s Confirmed, The 3I ATLAS is an Alien Space Craft!”. I am sure the mention of Musk is fake, only meant to attract more viewers. But the YouTube video on the website is fascinating, a mixture of science and sc-ifi. Click on the screenshot to watch the video.

Don’t worry. It’s a comet, not a disguised alien spacecraft.

Here is a promise. If humanity is still alive after November, I will write a post about the Fermi Paradox and the Dark Forest. And about my solution, the Rare Earth hypothesis.

Dwarf Planet 2017 OF201 and Planet 9

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In April 2016 I published a post Our Solar System, an update. At the end of this post I wrote about the New Horizons mission, that it was on its way to the Kuiper Belt, after a successful flyby of {luto.

Here is the Kuiper Belt, a ring of (mainly) small icy bodies orbiting the sun beyond the orbit of Neptune. The distance scales are in Astronomical Units (AU), where 1 AU is 150 million km. the average distance between Earth and the Sun. The locations of Jupiter, Saturn, Uranus, and Neptune are given. Earth and the other planets are inside the yellow blob in the center. The grey cloud between this blob and Jupiter represents the asteroid belt.

More than 3000 Kuiper Belt Objects (KBOs) have been found and that number is increasing yearly. Many of them are (relatively) small, like, for instance, the 2014 MU69, mentioned in my 2016 post as the next destination for New Horizons. Another flyby on 1 January 2019 was very successful. Here is an image of 2014 MU69, taken by New Horizons. It is a contact binary, dimensions ~40x20x10 km, now renamed Arrokoth. See the appendix about naming (and renaming) objects in the Solar System.

The official name for any object orbiting the Sun beyond Neptune is Trans-Neptunian Object (TNO). Some of them can be quite large. In 2005 Eris was discovered, with a diameter of ~2300 km, about 1/5th of Earth’s diameter, similar in size to Pluto. A heated discussion among astronomers led in 2006 to the demotion of Pluto as a planet and the introduction of a new concept: dwarf planet. Pluto was always an odd one out with its elliptical orbit. It is now a dwarf planet, like Eris. Here is the Outer Solar System.

More dwarf planets have been discovered in the region beyond Neptune. A fascinating one is Sedna, discovered in 2003. Its orbit is extremely elliptical, its distance to the Sun varying between 76 and 937 AU, far outside the Kuiper Belt. One orbit takes 11.400 years, Various estimates for its diameter, Wikipedia gives >1000 km. Here is the orbit of Sedna in orange. The Outer Solar System is now so tiny, the Kuiper belt is marked in blue.

Also shown is the orbit of 2012VP113, in red. Discovered in 2012, diameter ~600 km. Again very elliptical, distance to the Sun between 80 and 460 AU. One orbit takes ~4500 years. You may wonder how astronomers discover such a remote object and even determine some of its properties. In the picture you can see how. Three images, taken by a powerful telescope, with a 30-minute interval, have been superimposed. Look at the small dot in the center. That is 2012VP113, moving against the background of stars

One more extreme TNO, 2015TG387, was discovered in 2015. Its aphelion (the farthest distance from the SUn) is a staggering 2114 AU. The orbital period is about 40.000 years.

More of these extremely elliptical TNOs have been found. What can have been the cause? . Not the giant planets or the Kuiper Belt, they never come close enough to feel their gravitation.

In 2016, two astronomers, Batygin and Brown, came up with an interesting hypothesis. A planet with a mass of about ten times that of Earth, orbiting the Sun in an elliptical orbit between 280 and 1120 AU, orbital period of 5000 years, could explain the orbits. In the diagram, the orbit of this hypothetical Planet Nine is shown.

P[anet Nine has not yet been found and it will not be easy. Not all astronomers are convinced that it exists, but it generated a lot of interest in extreme TNOs.

Recently, a new one has been found 2017 OF201. First observed in 2017. Distance to Sun between  45 and 1630 AU. Orbital period 24.000 years. Here are again three superimposed pictures, this time taken with an interval of 1 hour. Estimated diameter ≈ 550 to 850 km.

In an appendix I will tell more about the interesting way this extreme TNO was discovered and how an estimate could be made about its size. The evidence presented was so convincing that on 21 May TNO 2017 OF201 was accepted by the authoritative International Astronomical Union (IAU) as a new dwarf planet. I flurry of articles in magazines and newspapers followed. Some are accurate, like the EarthSky one, others contain errors, like the Yahoo!News one.

Here the orbit of 2017PF201 is added in red to the other TNOs. The supposed orbit of PLanet 9, here called Planer X, is shown in black.

As you see, the orientation of this new TNO is completely different from the others! And that is a serious challenge for the Planet 9 theory. Model calculations show that Planet 9 would strongly disturb the orbit of 2017 OF201 and, in the future, would kick it out of the solar system. So, does Planet 9 really exist?

That was the ending I had in mind for this post.

But, very recently another interesting article was published, claiming that PLanet 9 may have been found! Click here for the original publication (quite technical). The idea is “simple”. Planet 9 will be cold, but still it emits (thermal) infrared radiation. The authors use data from two infrared missions, IRAS (1983) and Akari (2006), comparing them, filtering out all known infrared sources and looking for an area, that doesn’t move within a few months, the operating time of both missions, but is found in a different location after 23 years. They find one suitable candidate, which fits with the theoretical orbit of Planet 9. Amazing.

I am sure that this is not the end of the story 🙂 .

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Appendix 1 Naming/renaming of astronomical objects in the solar system

All astronomical solar system objects (except comets), smaller than planets, are called minor planets (planetoids). Asteroids, KBOs, TNOs, and dwarf planets. The Minor Planet Center keeps track of them. When a new minor planet has been discovered, it gets a name. For the new dwarf planet, this (provisional) name is 2017 OF201. Here is the explanation. 2017 was the year it was first observed. Followed by two letters.

The first letter, O, tells in which half-month of that year it was discovered, in the second half pf JUly 2017. The second letter gives the order of discovery for that half-month. The F would naan that it was the sixth minor planet discovered in that half-month. But wait. When this coding was designed ( in 1925), it could handle 25 discoveries in a half-month, but nowadays, with modern technology, there are many more. That’s why the subscript is added. 201 x 25 = 5025 +8 = 5033. This dwarf planet was the 5033th discovery in the second half of July 2017!

When the orbit is determined accurately enough, this provisional designation is replaced by a (sequential) number. The team that discovered the minor planet can then suggest a name. The minor planet 2014 MU69, visited by New Horizons, is now named 486958 Arrokoth. Using the coding given above, you should be able to check that Arrokoth was the 745th discovery in the second half of June 2014.

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Appendix 2 T The discovery of dwarf planet 2017 OF201.

The original article can be found here. The authors use data from the Dark Energy Survey project, which itself is not related to the solar system. To find objects in the solar system, you must look for objects that move. Using the survey data, already ~800 TNOs have been found. The next step is to find the distance of the object. For that we use the apparent motion of the object against the background of the stars. It is called parallax. Due to Earth’s orbit around the Sun, the position of the object changes. From how much it changes, the distance can be calculated. For 2017 OF201 this distance is at the moment about 90 AU.

The combined effect of parallax and real motion for 2017 OF201 is shown in this diagram

The oval (due to parallax) is moving throughout the years. Observation dates are indicated.

From the amount of light, combined with the distance, a rough estimate can be made of the size. For 2017 OF201 this results in a diameter of 550 to 850 km . Big enough to call the object a dwarf planet.

2025 is a leap year!

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Before you start protesting, we are not talking about the Western (Gregorian) calendar but about the Chinese one 😉 .

In the Western calendar, a year has 365 days, but one orbit of Earth around the Sun takes 365.25 days, 6 hours more! To compensate for this shortage, an extra day is added (29 February), when the year is divisible by 4. As 2025 is not divisible by 4, it is NOT a leap year. Have a look at Appendix* f for more details.

MoonThe Chinese calendar is a lunar calendar, based on the orbit of the Moon around the Earth. One orbit takes on average 29.53 days. Therefore, a lunar year is 12 x 29.53 = 354.36 days, 11-12 days shorter than the solar year.

As a result the lunar year moves forward 11-12 days yearly with respect to the solar year. The Islamic calendar is doing that.

Does that matter? It depends, for an agricultural society it does, because a lunar calendar has no relation with the seasons.

The solar year has seasons because the Earth’s axis is tilted. Here is a diagram. There are two times when the Sun is right above the equator. Day and night are of equal length all over the world. They are called the Spring equinox (~ 21 March) and the Autumnal equinox (~21 September). Around 21 June, the Sun reaches its northernmost position, the Summer Solstice, when daylight is at its maximum in the Northern hemisphere. Half a year later, the daylight is minimal. around 21 December, the Winter Solstice. (Of course in the Southern hemisphere it is just the other way around).

I wrote “around” and in the diagram a few dates are mentioned. In Appendix 2 I will explain why the dates vary, although the events are fixed.

Another way to describe the location of the Sun, is by using degrees (ecliptic longitude is the technical term).. We start at the Spring equinox (0°), and go counterclockwise. Then the Summer solstice is at 90°, the Autumnal equinox at 180°, and the Winter solstice at 270°.

Can we also divide the solar year in months? Sure, by dividing the Sun’s orbit in 12 sectors, each of 30 degrees. Each sector corresponds to a solar month. It is what the Chinese solar calendar does. It introduces 24 Solar Terms, two for each month, one for the start and one for the center. It is called the Center Point of that month. (similar to a Full Moon day in the lunar calendar). Here is a diagram of the 24 Solar Terms.

The diagram contains lots of information, the names of the solar terms (in English and Chinese) and the approximate dates. When you are Chinese, you may find a few familiar names: Qing Ming (15°), Dhong Zhi (270°) and Li Chun (315°). More about this in Appendix 3.

To explain the lunisolar calendar, we need the dates for the lunar and the solar months. Lunar data( for the years 2005-2045) can be found here and the Solar Terms (for the years 1900-2049) are here.

Here is the info for the first lunar month in 2025. The link above gives 29 January at 20:35 for the New Moon. So, the first month of CNY starts at 29 Januarty. The next New Moon is at 28 February, so the last day of the first month is 27 February.

The Solar calendar starts with Li Chun (the beginning of Spring). Using the Solar Terms link above, we find the date for that solar term: 3 February at 22:10, so the first solar month starts on 3 February. The next solar term (Rain Water) is at 18 February 18:-0, so tne Center Point is on 18 February. I have collected the results in the table below. The first lunar month contains the first solar center point.

I have done the same for the next two lunar months.More or less the same but the Solar Center Point shifts to more the end of the lunar month (8 resp. 7 days). That makes sense because a solar month is slightly longer than a lunar month.

Here are the other months for 2025. Notice the month I have given a blue color.

As you see there is a lunar month that doesn’t contain a solar center point!. When that happens, that month is considered a leap month. It just duplicates the earlier month. The result is that a lunisolar leap year contains 13 lunar months.

Notice how after the leap month the solar center point is at the beginning of the lunar month. Each lunar month it will advance 1-2 days, so after 2-3 years there will be another leap month. Not necessarily the sixth month, like this year. See Appendix 4.

In the Chinese lunisolar calendar, a lunar month is a leap month when it does NOT contain a solar center point.

Appendix 1 About a leap year in the Gregorian Calendar

A leap day is added when the year is divisible by 4. This makes the length of a year 365 + 1/4 = 365.25 days. But the solar year is actually 365.2422 days, slightly less. Therefore, the Gregorian calendar has a second rule: when the year is divisible by 100, it is NOT a leap year; This makes the average year length 365 +1/4 -1/100 = 365.244 days. A better approximation, but it can be made even better by a third rule: when the year is divisible by 400, it IS a leap year; making the average year length 365 + 1⁄4 − 1⁄100 + 1⁄400 = 365.2425 days. More information about leap years can be found here.

Appendix 2: Why do the dates for solar terms vary, while the events are fixed.

Because a normal year is 6 hours short of a solar year, the solar terms will shift 6 hours! Take for example Li Chun. In 2025 it falls on 3 Fberuary at 22:10, but in 2026 on 4 February at 4:02. Six hours later, so next year Li Chun will fall on 4 February. Another cause of variability is the time zone system we are using on Earth. All dates and times in this post are in China/Malaysia time (UTC + 8). in that timezone the Summer Solstice falls in 2025 on 21 June at 2:42. New York is using Eastern Time (UTC-4), the Summer Solstice in that timezone is 12 hours earlier and falls on 20 June 22:42, one day earlier.

Appendix 3 About Dong Zi, Qing Ming and Li Chun

The Chinese festivalls follow the Lunar calendar , with three exceptions. Around Qing Ming (Cheng Beng) Chinese families visite the graves of their ancestors. `And around Dong Zhi, Chinese celebrate the harmony in the family. Li Chun is of special imporatnce for the believers in Feng shui. All three belong to the solar calendar, they don’t move around.

Appendix 4: How to find a leap month

You don’t need mathematics to find a leap month, just the tables for moon phases and solar terms as given above. Solar Center Points advance relative to lunar months, so we must find a lunar month where the Solar Center point falls on the first day of that month. We have to continue until 2028 before we find a month that fits that condition. Here is the relevant part of the table for 2028

I2028 will be a leap year, the 5th month will be duplicated.

The Mandelbrot Fractal

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In the 1991 edition of the Guinness Book of Records the Mandelbrot Fractal is mentioned as Most complex object in mathematics? , with as explanation: A mathematical description of the shape’s outline would require an infinity of information and yet the pattern can be generated from a few lines of computer code.

Here is the Mandelbrot Fractal.

When you zoom in on the outline of the fractal, you will see more and more details.

And you will notice that there are smaller copies of the Mandelbrot.

Connected to the main shape in a complicated way.

Same shape, but often a bit distorted.

Infinite detail.

I learned about the Mandelbrot fractal around 1985 and got hooked right away ;-). On my PC I wrote programs to generate the Mandelbrot Fractal myself. In 1988 I attended a symposium organised by the Delft University, Fractals and Computed Art. I submitted one of my fractal images to a contest but didn’t win a prize :-(. I gave talks about the topic to my students and in 1990 to a group of senior citizens..

More than ten years later I built my own website and of course part of it was about fractals.One page, Fractals, describes in more detail than above my experiences with the Mandelbrot fractal. The page has many broken links. but is still worth reading . I also wrote a tutorial, (in Dutch). aimed at high school students, It became quite popular, because I had written a number of interactive Java applets, where you could play around with the various aspects of the Mandelbrot Fractal.

However, in the years that followed, it became more and more difficult (and now even impossible) to run Java applets, because of the security risks involved.

A few months ago, after talking with friends, I decided to translate the tutorial into English and look for a replacement of my applets. There are many interactive applications on the internet related to the Mandelbrot Fractal, but it took me time to find the ones that fit well with my tutorial.

I am very pleased with the final result. Click on the screenshot below to enter the tutorial.

Enjoy the beauty of mathematics!

The Toba eruption

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Here is a Google Earth image showing part of Sumatra with its capital Medan. The Malaysian coast is at the right with the harbour of Port Klang. Lake Toba, about 100 kilometres long, 30 kilometres wide, and up to 505 metres deep is the largest volcanic lake in the world. Volcanic? Yes, about 74.000 year ago, there was a volcanic eruption, the largest-known explosive eruption on Earth in the last million years. The eruption left a caldera, which is now lake Toba.

There exists a classification for explosive volcanic eruptions, similar to the Richter scale for earthquakes. It is called the Volcanic Explosivity Index (VEI). During an explosive volcanic eruption lots of (molten) rocks and ash (called tephra) are expelled into the air and it is the (estimated) volume of this tephra that is used to classify the eruption. Here is the VEI scale. Like the Richter scale it is logarithmic, each following step means a ten-fold increase in ejected volume. The “How often?” row gives an estimate of the frequency of the eruption, not surprisingly huge eruptions are very rare. There is an older classification of volcanic eruptions, Strombolian, Plinian etc, see Eruption Classifications. The last row gives an estimate of the plume height.

Here are a few examples

The Etna is Europe’s largest active volcano located in Sicily in southern Italy. On average it has a VEI index of 2. I visited this volcano twice, in July 1971 and July 1979. In 1971 it had erupted in April. Lava flows had caused a lot of damage and it was a special sensation to walk over solidified lava that was still hot under your feet. In 1979 it erupted in August but during my visit I still could climb up to the rim of the crater.

The Vesuvius volcano is also located in Italy, near Naples. It is not very active at the moment but erupted in 79 AD. spewing 3.25 km³ of tephra, destroying the cities of Pompeii and Herculaneum. VEI index 5. A catastrophic event.

And that is only VEI-5. Here is the island Santorini in Greece, Or rather what is left of it after a volcano erupted on the island circa 1600 BCE . The eruption volume is an estimated 34.5 km³, so the VEI index is 6. In the center of the caldera two small volcanic islands have been formed. There is still a lot of discussion about the exact date of the eruption, it may have caused the downfall of the Minoan culture.

VEI-6 eruptions are not rare, they occur globally with a frequency of 50-100 years. In 1883 the Krakatoa erupted (8–25 km³ ) . Similar to Santorini, in the resulting caldera a volcanic island, Anak Krakatoa has formed. In this photo seen in the foreground, with Krakatoa in the background.

The most recent VEI-6 eruption was Mount Pinatubo in 1991 with an erupted volume of 12.5 km³ Two photos, one taken about one month after the eruption, the other one taken in 2012, where a lake has formed in the caldera. What a contrast 😉

In recorded history there is only one VEI-7 eruption, Mount Tambora in 1815 with an eruption volume of 144–213 km³ Located on the Indonesian island of Sumbawa, it is now a tourist attraction. The caldera is 6-7 km wide and 600-700 meter deep.

VEI-7 eruptions are so powerful that the plume reaches the stratosphere. This can lead to a volcanic winter event. The lighter particles and ash fall/rain down, but the plume also contains massive amounts of gases like SO2 and H2S which in the stratosphere  react with OH and H2O to form H2SO4 (sulphuric acid) aerosols. They reflect the sunlight, remain in the stratosphere for months or even years and spread globally. The effect is a temporary climate change, affecting crops etc. The year 1816, one year after the Tambora eruption was a Year Without a Summer ! Average global temperature was 0.4–0.7 °C lower, causing major food shortages in many countries.

After this long introduction, it’s time to come back to the Toba eruption. Because it happened so long ago, the estimates of the ejected tephra are of course less accurate, they vary between 2000-13200 km³ A recent one gives 8600 km³. Meaning that the Toba eruption was at least a VEI-8 (more than 1000 km³) and possibly even a VEI-9 (more than 10.000 km³).

How much is 8600 km³? Well, if all that tephra would be deposited over Peninsular Malaysia, it would result in a layer of about 65 meter thick!

When you compare the Tambora eruption with the Toba eruption, Toba should have resulted in a much stronger volcanic winter, possibly lasting many years if not decades.

Could such a volcanic winter have affected our species, Homo Sapiens ? The Toba eruption happened during the Last Glacial Period . It was in that same period that waves of Homo Sapiens migrated out of Africa. This graph shows global temperatures during the last 150.000 years. The Eemian and the Holocene (our present era) are warmer Interglacials. During the Last Glacial Period temperature dropped as did the sea levels. See my blog posts Ice Ages and Sundaland. As you see in the graph, the temperature variations are rather irregular. There are markers for the Out of Africa waves and the Toba eruption

In this map the spreading of Homo Sapiens is shown (in red) together with the distribution of earlier human ancestors, the Neanderthals and the Homo Erectus. In 2012 I did a DNA-test to find out when my ancestors left Africa. For my paternal ancestor that was around 50.000 years ago, my maternal ancestor left earlier, ~70.000 years ago. Both after the Toba eruption. Here is my blog: My ancestors .

The Homo Sapiens population in Africa was small and the migrating groups even smaller, think about numbers in the thousands. They were hunter-gatherers. Sudden climate change might threaten their existence. The Toba Catastrophe Theory, developed a few decades ago, holds that the Toba eruption caused a global volcanic winter, leading to a near extinction of Homo Sapiens, causing what is called a (human) genetic bottleneck. Here is an illustration of a genetic bottleneck. Because only a small number of individuals survives the bottleneck, their genetic diversity is limited.

It is generally accepted that there have been many bottlenecks in the human evolution, Click here for an article about it. And a few months ago Scientific American published an article Human Ancestors Nearly Went Extinct 900,000 Years Ago That was the time of Homo Erectus, long before Homo Sapiens evolved.

The Toba Catastrophe is controversial. Did the Toba eruption produce a bottleneck? Was the Toba Volcanic winter so severe and long lasting that the global population of Homo Sapiens was reduced to about 1000 breeding pairs?

One vocal proponent of the Toba Catastrophe is Donald Prothero, an American geologist , paleontologist and prolific writer In 2018 he published When Humans Nearly Vanished about the Toba Catastrophe.

But here is an equally vocal opponent, John Hawks, an American paleoanthropologist with a popular blog, who wrote in the same year 2018: The so-called Toba bottleneck simply didn’t happen. He mentions research that humans thrived in South Africa during the Toba eruption.

I am not an expert, so don’t expect a verdict from me 😉

Nowadays Lake Toba and Samosir are tourist attractions of Sumatra. Here is a more detailed Google Earth image. Samosir was originally a peninsula until in 1907 a canal was opened through the isthmus.

I have visited Samosir in 1994, thirty years ago, I don’t remember much about it. Peaceful, interesting Batak culture. You don’t realise that you are staying on top of a dormant volcano. Deep below Lake Toba is a huge magma chamber (50.000 km³ ) that is filling up slowly with magma. This has lifted Samosir already around 450 m. Will there be another supervolcano eruption? Yes, but no need to worry, that may take another 600.000 years.

Sundaland

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One year ago I wrote a post about the Paleomap Project. At the end of that post I included a link to the Story of the Malay Peninsula. Here it is again. The clip is less than 3 minutes and worth watching.

I ended my post with: Notice how during the Ice Ages the sea-level was so low that the islands of the Malay archipelago were connected. This was called Sundaland. Topic for another post.

Here is my post about Sundaland.

What is actually an Ice Age?

Probably most people will first think about the funny Ice Age movies, but hopefully many will also know that there has actually been a period in Earth’s history, where the climate was cold and a large part of the Earth (North America, Europe) was covered with ice. That was about 21 thousand years ago and it is commonly called the Ice Age. Here is a Paleomap of Earth during that time.

Notice that the map doesn’t say Ice Age, but Last Glacial Maximum ! I got interested, Googled a lot and wrote a separate post Ice Ages. Here is a summary.

  • In the 4.5 billion years of its existence, Earth has been mostly (~85%) a Greenhouse, no icecaps, icesheets, glaciers. But there have also been at least five major periods that Earth was an Icehouse, partially covered with ice. These Icehouse periods are called Ice Ages. At this time Earth is in the Late Cenozoic Ice Age, which started 34 million years ago.
  • In an Ice Age there is always permanent ice, but the amount fluctuates. There are periods that the ice advances, they are called glacials. And there are periods that the ice retracts, called interglacials.
  • The last glacial was about 21.000 years ago and is often called the (Last) Ice Age. At the moment we are living in an interglacial, icecaps, icesheets, glaciers are retracting. But Earth is still an Icehouse.

There have been numerous glacials and interglacials in those 34 million years. Here the global temperatures for the latest are shown. Notice that the timescale is from right to left, so the last glacial (“the Ice Age”) is the rightmost snowflake. And there is an obvious regularity with a period of roughly 100.000 year. If you want to know more about the theory, read the Milankovitch Cycles article in Wikipedia.

In this blog we are especially interested in sea levels. During a glacial a lot of water is frozen in icecaps, icesheets and glaciers, so the sea level drops, and during an interglacial ice melts and the sea level rises. Here are the sea levels during the last 400.000 years. In the original graph time goes from left to right, I have flipped it to make comparison with the temperature graph easier. Notice the similarity between temperature and sea level. During interglacials sea levels were about the same as nowadays, but during glacials they were up to 120 meter lower.

I will now concentrate on the last 150 thousand years, Here is a more detailed temperature graph. Starting from the left, we see the end of the Penultimate Glacial at about 135 thousand year ago. It was a very cold one. Then, relatively quite fast, temperatures are rising, until they reach a maximum at 125 thousands year ago in the Eemian Interglacial. Warmer than nowadays, sea level 6-9 meter higher (!) than today. After this maximum, slowly and irregularly , temperatures are dropping, until a new glacial maximum is reached, about 21 thousand years ago. After this the temperature rises again and we reach the Holocene interglacial in which we are living nowadays.

This time period is very interesting for homo sapiens. Indicated are two waves of migration out of Africa. And about 74.000 year ago the Toba volcano on Sumatra erupted, one of the largest eruptions in Earth’s history. Present day Lake Toba is occupying the caldera of this eruption. There is a theory that this eruption almost caused the extinction of homo sapiens, but this Toba catastrophe theory is something for a separate blog.

We zoom in one more time and look at the sea level. It was 120 m below present during the last glacial maximum, then rising more or less gradually until it reached present levels around 6000 years ago. Around 12-14 thousand years ago, there was an interruption with a cold period (Younger Dryas). Also notice the steep increase around 14 thousand years ago, caused my melting icesheets , about 5 cm per year !

A sea level rise of 120 meter is enormous. Here is a Google Earth screenshot of South East Asia. The color of the sea indicates how deep it is, light blue is shallow, dark blue deep. When you open Google Earth on your computer and move your cursor over the screen, the depth is indicated. I have done that for three locations, and found 50, 30 and 40 meter.

When the sea level drops 120 m, the whole light blue region would become land!

Here is how the region would look like, 21 thousand year ago. Sundaland! A continental shelf, exposed when the sea level is low. If there had been public transport in those days, you could have traveled overland between Indonesia, Malaysia, Thailand, Cambodia en Vietnam! And in the far future, during the next glacial, that will be possible again 😉 .

Here is a video, where you can follow Sundaland from the last Ice Age until present. Only 44 seconds, worth watching. Created by Dhani Irwanto, more about him later.

There are more regions on Earth where something similar has happened. In the lower right part of the video, you can see part of the Sahul shelf. During the last Ice Age Australia and New Guinea were connected.

And in Europe during the last Ice Age, England, Ireland and mainland Europe were connected. The continental shelf is called Doggerland. Around 6500 year ago England became an island (again).

One more example. During the last Ice Age Tamil Nadu and Sri Lanka were connected. In this Google Earth image I have roughly marked the contour line (isobath) of 120 m below sea level. Some land is now submerged but not a continent as some Tamil nationalists still believe. See my blog Kumari Kandam & Lemuria.

Sundaland is a huge landmass (~ 1.8 million km2), now partially submerged. but large during the time that homo sapiens migrated out of Africa. Here are some of these Early Human Migration routes.

1in 2012 Aric and I took part in the Genographic Project , we sent samples of our DNA and got it analysed. It resulted in this map with the routes followed by our (maternal) ancestors. Read my blog My Ancestors for more details.

As you see there are migration routes to South East Asia and Sundaland. Could it be that during this last glacial there was a civilisation in Sundaland, later destroyed by the rising sea levels? Could that have been the lost continent, Plato’s Atlantis? Or the Garden of Eden?

In the last few decades, three books have been published advocating exactly that. In 1999 Stephen Oppenheimer published Eden in the East. According to him it was Sundaland where the first human civilisation started. After Sundaland became flooded (Noah’s flood!), the population dispersed and fertilized the cultures of Mesopotamia, Egypt, China and India. A few years later, in 2005, Arysio Santos published Atlantis, the lost continent finally found. Santos was convinced that Sundaland was the Garden of Eden and Plato’s Atlantis. Quite recently, in 2019, Dhani Irwanto published Sundaland: Tracing The Cradle of Civilizations. Same approach. All these books are still for sale at Amazon.

It’s a fascinating topic, and there is no doubt that Sundaland existed. But Atlantis, the Garden of Eden, the Cradle of Civilisation? Here is some information about the authors.

  • Stephen Oppenheimer (1947-) is a British paediatrician and geneticist. After 1997 he started a new career as a researcher and popular-science writer on human prehistory.
  • Arysio Santos (1937-2005) was a Brazilian nuclear engineer, but “his true hobby in life was researching arcane subjects such as Symbolism, Alchemy, the Holy Grail, Comparative Mythology and Religion” (quote from his own website)
  • Dhani Irwanto (1962 -) is an Indonesian hydro civil engineer. Founder of Indonesia Hydro Consult in 2010 and its director until now. Became interested in Sundaland and has written books about it.

The authors have in common they have no formal training in the subject matter. They were captivated by the subject and delved into all aspects of it, climatology, geology, linguistics, anthropology etc. Their approach, especially Irwanto’s, tries to be scientific. But it is still Fringe Science, outside the mainstream discipline.

I was considering to buy Irwanto’s book, but then I discovered a video Tracing the Cradle of Civilisations in Sundaland, about a lecture he gave in the Philippines in 2017 at an Asean Advanced Archaeology Symposium. Brilliant presentation, worth watching (28 minutes).

But he is really going too far in his enthusiasm. Here is a screenshot from the video. Everything, all over the world , originated in Sundaland. So I may not buy the book.

Ice Ages

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What is an Ice Age? And how many Ice Ages have there been on Earth? I came across these questions, while writing a blog post about Sundaland. During the Ice Ages the sea level was much (~ 120 meter) lower than at present and the islands of the Malay archipelago were connected to Thailand, Cambodia and Vietnam. This landmass was called Sundaland. In my blog Sundaland (still under construction) I write in more detail about it.

If what follows is too detailed for you, just jump to the summary

During the 4.5 billion years that Earth existed, Its climate has fluctuated between Greenhouse and Icehouse. During a Greenhouse there were no glaciers, no icecaps (South Pole), no Ice sheets (Greenland) no permanent sea ice (North Pole). Earth was mostly a greenhouse , about 85 % of the time. Temperature was (a lot) higher than at present. Sea levels higher, sometimes 300-400 meter. Lots of carbon dioxide in the atmosphere. Tropical rain forests on the South Pole 😉

But there also have been Icehouses, often called Ice Ages, where glaciers, icecaps and ice sheets were permanently present. Scientists have identified 5 of them. Here they are marked on the 4.5 billion year timescale that Earth existed.

The Hadean, Archean and Proterozoic are the first three “aeons” of Earth’s geological history. We are now living in the last aeon , the Phanerozoic, which started ~ 542 million years ago, the name is too long to be named in the image. Before I “zoom in” on this last aeon, a few comments, related to blogs I wrote in the past.

  • Only a few million years after the formation of Earth, in the Hadean, our Moon was “born” as a result of a collision of Earth with another planet. Where does the Moon come from? .
  • The oldest fossils date back to the Archaean, 3.4 billion years ago, when Earth was still young. Therefore many think that life comes easily and must be ubiquitous in the universe. I am sceptical, see my blog The Drake Equation.
  • It took a long time before those simple cells evolved and developed a nucleus that contained the DNA, about 2,2 billion year ago in the Proterozoic. And it took even longer for multicellular organisms to develop, about 600 million year ago, at the end of the Proterozoic. See my blog The Tree of Life.

The Proterozoic had two Ice Ages. The Huronian actually consists of several separate Ice Ages and lasted about 300 million years The Cryogenian also has two separate Ice Ages, together lasting about 85 million years. The Cryogenian was severe, there may have been periods that Earth was completely covered with ice, a so-called Snowball Earth.

.Keep in mind that Earth looked very different in those days because of plate tectonics and continental drift. See my blog The Paleomap Project. Here is one of Scotese’s maps: Earth during the Cryogenian Ice Age.

Now let’s zoom in on the Phanerozoic, from 542 million year ago until present. The ‘official’ start of this aeon is 538.8 million year ago. This beginning was chosen because around that time a sudden , explosive diversication of life forms started, the Cambrian explosion. Multicellular organisms evolved into a multitude of species. Here is an artist impression.

The Phanerozoic had three major Ice Ages, the Andean-Saharan, 440 million years ago, lasting 40 million years, the Karoo , 300 million years ago, lasting 100 million years and the current one, the Late Cenozoic Ice Age , which started 34 million years ago and is still ongoing.

Here is a (complicated) graph of the global temperature during the Phanerozoic. Complicated because the timeline has been split in five parts, zooming in.

The first part (in red) covers from 542 Million years (Ma) until 66 Ma. The temperature data are less reliable, but you can see the Andean-Saharan (440), the Karoo (300) and an unnamed one (~180). Next comes the green part, timeline enlarged about 10 times, from 66 Ma until ~ 5 Ma. Around 66 million years ago a huge asteroid collided with Earth, causing the extinction of the dinosaurs and giving mammals the opportunity to develop. Earth was a hothouse then with a maximum temperature around 55 million years ago (PETM). After that maximum, global temperature started to decrease. Around 34 million years ago, Antarctica got an icecap and Earth became officially an Icehouse, the Antarctic Glaciation . The next zoom in (again x10, in black) shows how the cooling of Earth continued. Around circa 2.58 million years ago the Pleistocene started, ice “everywhere”, also in the Arctic region.

The next part, in blue, shows in more detail the last one million years of Earth. It’s clearly an Icehouse but there are periods which are colder (glacials) alternating with warmer ones (interglacials). If you would be able to watch Earth during this one million years, you would see the icecaps and ice sheets advancing during glacials and retreating during interglacials. The last of these “warmer” interglacials was the Eemian (130-115 thousand year ago. Followed by the last glacial (26-20 thousand years ago). It is this last glacial that is often, called the Ice Age.

At present Earth is in an interglacial, as can be seen in the last part of the graph (also in blue). This interglacial started around 12 thousand years ago and is predicted to continue for many thousands of years. These predictions are based on the theory of Milankovitch cycles, a bit to complicated to explain here. It may last 50 thousand years, or even longer because of human interference (climate change!). After the interglacial, a new glacial will start, because Earth is still an Ice House.

Summary:

  • Earth is an Ice House already for 34 million years. An Ice House (also known as Ice Age) consists of many glacial (colder) and interglacial (warmer) periods, each lasting thousands of years.
  • The last glacial period occurred 26-20 thousand years ago and is often called the ICE AGE.
  • At the moment Earth is in an interglacial and that will last for many thousands of years, possibly even longer because of human interference.

Of course there is a lot of information available these days about future climate developments. Not always reliable !

Here is a very dishonest one, A New ICE AGE Is Coming: Prepare To Freeze By 2050! A lot of factually correct information, leading to a ridiculous ending. Click on the link to watch the video, AYOR!. His advice: Pump more greenhouse gases into the atmosphere to avoid the impending next Ice Age (~ 2050!).

Here is a much more interesting one, New Evidence We Are Entering An Ice Age Termination Event Glacials have been ended numerous times by termination events. We are in an interglacial now, but it looks different this time. Could this be the start of a Hot House. We just don’t know.

Life on Europa & Enceladus?

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It is generally assumed that you need liquid water for life to develop. The planet Mars is now dry and arid, but had lots of water in its far past.. The Perseverance rover (see my blog) is at the moment collecting samples of Martian soil, hoping to find fossil remains of (microbial) life, until now without results. Disappointing for those who are convinced that “simple” life must be ubiquitous in the universe.

When you have been following my blog, you will know that I am not really surprised. Personally I think that (simple) life will NOT develop easily, even in a suitable environment. See my recent post about the Drake Equation.

Are there other places in our solar system with (abundant) liquid water? Yes, there are, here are two, Europa and Enceladus. Europa is a moon of Jupiter and Enceladus a moon of Saturn. Europa is large with a diameter of 3122 km, only slightly smaller then Earth’s Moon (3475 km). Enceladus is much smaller, with a diameter of 504 km. In this image you see the relative sizes of Earth, Moon and Enceladus,

Here are the two moons, Europa left and Enceladus right.. Both moons are covered with a thick crust of water ice. This ice surface has a temperature of about -200 degree Celsius. But underneath this crust both moons have oceans of liquid water!

We think that the interior of the two moons look like this. Europa has a metallic core (iron and nickel),a rocky mantle and a (salty) ocean with an estimated depth of 60-150 km.. A thick ice crust ( 15-25 km) covers the ocean. The model shows the layers to scale.

Enceladus has a rocky core with radius of ~ 180 km , covered by a 30 km deep ocean. and a 20 km thick crust. The ice crust is thinner at the south pole.

How is it possible that these moons have liquid water under their ice crust? Where does the energy come from, the Sun is far way. The answer is: because of the tidal forces exerted by the giants Jupiter and Saturn on their moons.

Newton’s gravitation between two objects depends on the distance between them. For example the gravitational force exerted by the Moon on Earth is stronger on the side facing the Moon than on the other side. This difference is responsible for the tides. The tidal friction will slow down the rotation of Earth , so the length of a day will increase a little bit, about 1,8 millisecond per century. In the far past when the moon was born, the day length may have been about 4 hours only!, For the moon the story is similar: tidal friction has slowed it down, even a lot more, the Moon shows always the same face to Earth, it is “tidally locked”. Actually all the major moons in the Solar System are tidally locked to their planet.

Even tidally locked moons still can undergo tidal flexing, if the orbit is elliptical, a kind of kneading. Model calculations for Europa and Enceladus indicate that this .can generate enough energy to keep the oceans liquid. More (technical) details here.

So both moons have liquid water and a source of energy , two of the essential ingredients for life as we know it. The third ingredient (chemicals like carbon, hydrogen, nitrogen, oxygen, sulfur, and phosphorus) should be available in the rocky core.

The information about the two moons comes basically from two successful space missions. The Galileo spacecraft arrived at Jupiter in 1995 and stayed in orbit until 2003. It’s main mission was to study the planet, but it managed to have numerous flybys’ of Europa. The Cassini entered Saturn’s orbit in 2004 and stayed there until 2017.

The Cassini mission was very successful, click here for an overview. One of the most spectacular discoveries was that Enceladus is an active moon. There are geysers in the south polar region of the moon! This picture was taken by Cassini in February 2010.

The geysers consist of water vapor and ice particles. The explanation is that water seeps from the ocean floor into the rocky core where it is heated. The heated water rises and erupts though fissures in the icy crust.. It is a bit similar to the hydrothermal vents in Earth’s oceans.

There are indications that Europa also has this kind of geyser activity, although less intense Here is a recent (2021) NASA report, Are Water Plumes Spraying from Europa?

In the search for extraterrestrial life these two moons have top priority. Many proposals for missions to Europa have been formulated and later discarded, here is a list. At the moment the Europa Clipper is being prepared for a launch in October 2024. It will arrive at Jupiter in April 2030. Here is an artist’s concept, of Clipper, Europa and Jupiter. The solar panels of Clipper span 30 meter!

The artist impression might suggest that the Clipper will orbit Europa, but that is not the case, it will orbit Jupiter in an elliptical orbit and make 44 flybys of Europa. It will study Europa’s icy crust, find confirmation for the ocean underneath and try to make flybys through the geysers (if they exist).

A proposed follow-up mission is the Europa Lander. It would land on Europa, collect some material from the icy crust and search for biomarkers, signs of life. Here is another artist impression. Notice the geyser at the horizon 😉 .

Probably the Europa Lander mission will be cancelled. Why? Because Enceladus offers better options than Europa. The main difference is that Enceladus is continuously spewing water and ice crystals, whereas the geysers of Europa are sporadic and still have to be confirmed.

The reason that there is so much interest in the geysers is obvious. To find out if there is life in these oceans, we have to drill through a 15-25 km thick ice crust first. Actually there are studies how to do that, they read like science fiction. Here is the final report (pdf file, 70 pages, 2019) about the Europa Tunnelbot. The basic idea is that this tunnelbot would melt itself down through the ice crust of 20 km in 3 years time, to reach the ocean. Here is a artist impression from the report, I have rotated it 90 degrees, to fit better in this post. Left is the icy surface of Europa, the inset shows three “repeaters” because even when the bot reaches the ocean it still must transmit date to the lander.

Science fiction and I think it will never happen, because the geysers on Enceladus and possibly on Europa may already give information about life in the oceans below the crust!

After Cassini observed the geysers on Enceladus, the scientific program was adapted and the spacecraft went a few times through the plumes. It found water, ice crystals and organic compounds!

So that will be the program for the next decades, explore Enceladus and find out whether the geysers will have convincing biomarkers.. .

Of course it will take time to design Enceladus missions. Here is one, the Enceladus Orbilander. Approved as a so-called Flagship Mission. Still in the design phase. possible launch in the late 2030s Arriving at Enceladus in the early 2050s.

First it will fly numerous times through the geysers, collect material and analyse it. Then it will land at the South polar region.

This is the South polar region of Enceladus. The “tiger stripes” are fissures in the ice crust where geysers erupt.

And here is an artist impression of the Orbilander on the surface of Enceladus.

Until now life has only be found on Earth. Discovery of (primitive) life elsewhere in our solar system would be dramatic, because in that case we would know that (intelligent) life is ubiquitous in the universe.

At the moment Perseverance is collecting soil samples on Mars which will be brought back to Earth by the Mars Sample Return Mission around 2033. At about the same time Clipper will explore Europa. So we will have to wait for 10 years and for results from Enceladus about 30 years.