The Week in Space and Physics: When Worlds Fall Apart
On disintegrating planets, exocomet clouds, moon landers, and the end of Gaia.
Icarus might be an appropriate name. Two weeks ago, astronomers announced the discovery of a bizarre planet around a nearby star. Like many exoplanets it orbits far closer to that star than the Earth does to the Sun - though in this case, it seems the planet has gotten a little too close for comfort.
The study found a long stream of debris stretching far into space behind the world, almost like the tail of a giant comet. That, astronomers reckon, may be a sign the planet is melting and disintegrating under the heat of its sun. Certainly it is close to that star – completing a full orbit in just thirty hours – and it must be experiencing intense heat.
Planets that venture too close to a star can be ripped apart by immense tides. Yet this world is far enough to be spared that fate. Instead its surface is melting, forming oceans of lava and a thin atmosphere of vaporised rock. Under the pressure of stellar winds that is being stripped away, lost into space as a long comet-like tail. Based on the size of the tail and presumed mass of the planet, complete destruction of this world could come in no more than two million years.
Weirdly, however, this seems to be happening in an ancient solar system. Something must have pushed this world inwards, away from its old orbit. That can happen by chance: the orbits of the planets are not stable over long periods of time, and it is possible Mercury or Venus could one day fall into the Sun. But it might also be happening under the pressure of another star, one that has slowly pushed the planet into its sun.
That was not the only disintegrating planet reported on in recent weeks. K2-22b is a planet about the size of Neptune, lying around eight hundred light years from Earth. It was first seen in 2015, when its discoverers noted how close it lay to its star. Observations then suggested it could be falling apart, leaving a tail of debris behind it.
Last year, the James Webb telescope took a closer look at the tail. It found signs of metallic debris, just as would be expected if it were coming from the interior of a planet. Yet traces of other molecules were also present, which, the astronomer Nick Tusay says, shows the planet is probably clinging on to some of its outer layers.
If so, those layers seem to be made of ice and snow, and possibly of the kind that might be found at the bottom of oceans on a water world. As before, then, this may be a world that formed in a cooler place, until it somehow chose, like Icarus, to fly a little too close to a star.
Charting the Exocomets
On April 5th, an observatory in Chile spotted a new comet. Over the following months observers tracked it as it moved closer and became brighter, travelling inwards from the outer solar system. By the start of January it had become visible to the naked eye, and astronauts on the space station captured photographs of its elegant tail.
Measurements of its orbit showed the comet was old, and that it had probably spent over fifty thousand years falling towards the Sun. But on January 18th that long journey came to an end. Under the heat of our star the comet broke apart, disintegrating into a shining cloud of ice and dust.
Comets like this originate at the fringes of interstellar space. There, stretching for hundreds of millions of miles around the Sun, is a ring of shattered ice and rock. From time to time disturbances in that cloud – perhaps from passing stars or random encounters – send a lump of ice falling inwards. After a journey of up to half a million years, that ice encounters the Sun and produces the streaming tail we so associate with comets.
Such clouds of ice and rocky debris seem to be common around stars. They are large, which should make them easy to see, but they are also cold and dark, which means they are only visible with telescopes designed to look for long wavelengths. Specialised observatories, such as the ALMA telescope of northern Chile, are thus needed to find them.
In a recent paper, a team led by Luca Matrà at the University of Dublin reported an effort to chart as many of these clouds as possible. They observed more than seventy such clouds lying within five hundred light years of Earth. Among them was a wide mixture of structures, with some appearing as narrow rings and others as surprisingly broad.
There is still much we don’t understand about these icy clouds. Models of the history of our solar system suggest they originated as debris from the formation of the planets, scattered outwards by the gas giants. At some point in the distant past they seem to have rained inwards, bringing a period of intense comet impacts and perhaps forming the oceans on Earth, Venus, and Mars.
All that hints these ice clouds played an important role in the birth of the planets and the origins of life. But whether this holds true around other stars is still to be studied. The sheer variety of their structures alone already tells us astronomers will have plenty of work to do.
White Rabbits and Blue Ghosts
A pair of missions launched towards the Moon in the early hours of January 15th. The two spacecraft shared a ride on a Falcon 9 rocket, but are now following separate paths towards the lunar surface.
First to reach the Moon will be Firefly’s “Blue Ghost”. According to the company, the probe will take about six weeks to get there, with a first flyby of the Moon taking place in mid-February. A landing is currently planned for March 2, though that date might slip if any unexpected issues crop up.
That would not necessarily be a surprise. Landing on the Moon is hard. Several companies have tried in recent years, none have been fully successful, and this is Firefly’s first attempt at putting anything on the surface. If Blue Ghost does make it, they hope to survive for at least fourteen days after touchdown. In that time they will conduct various experiments, primarily for NASA.
After will be the turn of iSpace’s Hakuto-R lander, named after the white moon rabbit of Japanese legends. Like Firefly, they expect to make a flyby of the Moon in February. But they will then spend several months testing manoeuvres in deep space before finally heading back to the Moon. Their landing could then take place around the start of June.
Unlike Firefly, iSpace has been to the Moon before. But their first attempt, made in April 2023, failed after a software bug sent the lander plummeting towards the surface. If this time goes better, the company hopes to then deploy a small rover to explore the surface and send back data to Earth.
Gaia Ends Operations
On January 15th, ESA’s Gaia spacecraft reached the end of its ten-year long mission to map the Milky Way. Over the past decade Gaia has charted the position of two billion stars, an effort that has produced the largest and most detailed depiction of our galaxy ever made.
That naturally resulted in a multitude of discoveries. According to ESA, Gaia has given us the first clear view of the size and shape of our galaxy, helped chart out its history, and revealed clues as to its future direction. It has measured the orbits of over a hundred thousand asteroids, mapped a million quasars in the distant universe, and discovered everything from black holes to exoplanets.
In all, the telescope collected about five hundred terabytes of data. That will take time to process. So far, indeed, scientists have only worked through a third of what it has sent back. The coming years will thus see more results and discoveries from Gaia, with its final data release not expected until 2030.
Thank you for sharing this information. Your description of a molten planet spilling its lava like a comet was a readers dream. I am also glad to know that Japan relaunched its robot to attempt to do its thing on the moon after its first failed attempt.