The Week in Space and Physics: The Europa Clipper
On the Europa Clipper, Starship, the Nobel Prize and a return to Didymos
As the astronomer Galileo saw it, Europa is a world a little smaller than the Earth’s Moon. Of Jupiter’s four large moons it is the smallest, and it is the second closest, after Io, to the gas giant. We know, too, that Europa is tidally locked to Jupiter. From its surface that planet appears as an unchanging marker in the sky, around which the Sun, stars and other moons of Jupiter would come and go.
By itself, none of that is especially interesting. The solar system is full of moons that look like Europa, and many of them at first glance seem more worthy of study. Io, for instance, is a world riven by violent volcanic eruptions, the result of extreme tides induced on the moon by Jupiter. Titan, the moon of Saturn, has a surface of liquid lakes, and may be the only place in the solar system other than Earth to experience rainfall.
Yet there is something else about Europa. Its surface, as seen by Voyager 2, is bright and reflective, which can only be explained if it is covered in a thick layer of ice. The smoothness of that ice - seen up close by both the Voyager and Galileo probes - hints at some kind of activity, something acting to resurface the world over geologically short timespans.
Under the ice there is almost certainly a deep ocean, one filled with warm, salty water, and which might be one of the most habitable places, beyond Earth, in our Solar System. Indeed, some calculations say this ocean could sustain a modest biosphere - by no means one as complex as Earths, but one significant nonetheless.
Of course, there are many open questions here, and the habitability of Europa is far from a sure thing. We do not know how deep any ocean is, nor whether it has the right chemicals and temperatures for life to appear. And even if the ingredients are there, we do not know if this inevitably means life will emerge or thrive.
We should soon have answers to many of these questions. Last week NASA launched the Europa Clipper, a probe that will spend several years studying Europa. Its goal, NASA cautions, is not to find life, but rather to study the moon and establish whether it could be habitable.
After it arrives at Jupiter, which should happen in April 2030, the probe will make around fifty passes over Europa, each of which will give scientists a close-up look at the moon. Researchers hope to thus deduce the size and depth of its ocean, and to look for signs of the essential chemicals needed for life.
Of special interest are regions of Europa’s surface which appear chaotic, perhaps because of some internal activity. One possibility is a kind of volcanism, driven not by molten rocks, but by liquid water. If this is the case, it may imply the icy shell is thin and that the ocean is within touching distance of future probes. It would also raise the possibility of capturing an eruption in action, and thus of sampling the water bursting out.
Still, it seems unlikely that Clipper will actually find life on Europa. That, if it exists at all, is hidden far under the moon’s icy surface. But if it does find hints of life, then Europa is likely to remain a subject of fascination for decades to come.
For paying subscribers I plan to later this week publish a more in-depth look at Europa, Clipper, and the possibilities for life in Europa’s oceans.
Starship - A Catch to Remember
It was, to be frank, astonishing. On October 13, SpaceX launched the fifth test flight of Starship, the most powerful rocket to ever fly. As in the previous two flights, the superheavy booster flew almost without flaw, powering the Starship upper stage well beyond the official boundary of space.
That job done, however, and the booster then did something remarkable. Rather than falling back into the ocean, as is traditional for such gigantic machines, SpaceX steered the rocket back to its launch site. Incredibly, they then caught the booster, landing it on a pair of “chopsticks” held by a tower.
SpaceX thus demonstrated, for the first time in history, the ability to launch and then land a superheavy rocket. Future test flights will no doubt refine the technique, and iron out some of the kinks seen in the first catch. But it is a tremendous thing that SpaceX managed to do it at all, and that they did so on their first attempt at such an audacious goal.
Put the superlatives aside though, and what does this mean for the future of space exploration? In time, a reusable superheavy booster should dramatically cut the cost of putting hardware in space. That, in turn, should make it easier to put things like space stations and telescopes in orbit, and to send things to the Moon, to Mars, and beyond. It could, in short, be revolutionary - but whether it really will be remains to be seen.
Indeed, there is still a lot of work for SpaceX to do. They obviously need to show they can consistently catch the booster, and that they can refurbish and refly it. They also need to work on the Starship upper stage. In the last test it made it through the atmosphere to a controlled landing over the ocean. But it did suffer damage as it fell back to Earth, and it is still some time away from being able to come back to a landing pad, as SpaceX hopes it will one day do.
Perhaps the biggest task, however, is to prepare Starship for a moon landing. NASA is paying SpaceX to use Starship in Artemis III, the mission that should see astronauts walk on the Moon for the first time in half a century. For that, SpaceX will need to get Starship to orbit, show that it can be refuelled in space, and that it can land on the Moon and then take off again. There is, in short, a lot more excitement to come.
The Nobel Prize for … Physics?
In 1912 the Nobel Prize was awarded to Nils Gustaf Dalen, a man who was neither physicist nor scientist. He was instead the managing director of a firm that built lighthouses, and his prize was given for the invention of a type of valve used in the gas lights of those lighthouses.
Suffice it to say, then, that the Nobel Prize in Physics has not always been awarded for breakthroughs in, well, physics. Neither have the awards always been free of controversy, or recognised everybody they should have. Jocelyn Bell - discoverer of the pulsar - was notably excluded from the 1983 prize, which was instead awarded to her supervisor Antony Hewish, who had at first dismissed her discovery.
In this context, the awarding of the 2024 Nobel Prize does not look so bad. It was given to two men, John Hopfield of Princeton and Geoffrey Hinton of the University of Toronto, for their contributions to the development of machine learning. Their insights, made through physics based models and statistics, helped fuel the current rush of AI technology. But they are not, as many have pointed out, really contributions to the field of physics.
The Nobel Committee may have done better to accept their work fits better in the realm of computer science. There is, of course, no Nobel for that - but there are other prizes, both prestigious and more suitable. Put that criticism aside, however, and it remains that both men have done important work. They have - whether it will prove for good or for ill - surely helped shape the future of humanity.
Hera Heads for Didymos
Back in September 2022, NASA crashed the DART spacecraft into Dimorphos, a small “moon” of the larger asteroid Didymos. The idea was to test methods for changing the path of an asteroid, a technique that might one day be needed to save our planet from a devastating impact.
Follow-up observations showed DART had been rather successful, and the orbit of Dimorphos around Didymos had indeed been changed as NASA had hoped. At the time DART was accompanied by a smaller probe, LICIACube, which snapped a few images of the aftermath of the collision.
Now, however, a more sophisticated probe has been sent. Last week the European Space Agency, ESA, launched Hera, a spacecraft expected to reach Didymos at the end of 2026. If all goes to plan, Hera, along with two small cubesats, will investigate the post-impact state of Didymos and Dimorphos in detail.
That burning question: how common is basic life? Beyond that: how common is intelligent life? I've come to believe the odds on the latter are incredibly small, but the former seems more possible. Finding it in this star system would suggest it's very common.
Europa: Likely a warm ocean, maybe containing more water than all of Earth's oceans combined but the icy crust may have very uneven thickness- best to shop for an optimal place to land a mining probe. Odds of finding life..very good indeed.
SpaceX:. Outstanding engineering, but in the end wrongheaded to worry so about getting humans out into space. Instead send our robotic emissaries. It's a matter
of economics.
Nobels: computer science exists in a rather strange hinterland between physics, electrical engineering and pure mathematics. It's an enormous success and no doubt deserves it's prize. It's interesting that Hinton at least worries about the dangers inherent in his own creation.
Didymos:. All hail the cubesats- the unsung heroes of space exploration! One could write a book on their exploits (and Springer Verlag does have an excellent one available). Small but mighty and you don't need a Starship to launch them out of the gravity well!