planetary science

Mars’ moons could be the remains of an ill-starred asteroid that got too close to the Red Planet.

A shredded asteroid origin could help explain mysterious features of the small, odd-shaped moons, scientists suggest in the January issue of Icarus.

Where most moons are big round orbs, Mars’ Phobos and Deimos are small lumpy potatoes.

There are two main ideas for how the moons formed. One is that the moons actually were asteroids that were caught by Mars’s gravity. But that idea doesn’t explain the moons’ circular, stable orbits around Mars’ equator. More

The first samples from the farside of the moon contain signs of surprising volcanic activity near the lunar south pole.

Two separate analyses of lunar rocks brought to Earth by China’s Chang’e-6 spacecraft show the rocks formed from cooling magma relatively recently, about 2.8 billion years ago, according to papers published November 15 in Science and Nature. The measurements may help solve the mystery of why the moon’s farside is so different from its nearside, but also raise new questions about the history of lunar volcanism. More

Some of Uranus’ apparent oddities might be due to bad timing.

In 1986, the Voyager 2 spacecraft flew past the planet, recording mysteries of its magnetic field. Turns out, Uranus may have just been in an unusual state. A solar wind event days before the flyby compressed the giant planet’s magnetosphere, researchers report November 11 in Nature Astronomy. That compression could explain several long-standing puzzles about Uranus and its moons, and could inform planning for future missions (SN: 4/20/22). More

Most of Earth’s meteorites can be linked to just a few collisions within the asteroid belt between Mars and Jupiter, two new studies report, including a particularly cataclysmic impact event around 470 million years ago.

The upside to this discovery, published October 16 in Nature, is that it provides researchers with vital context: By knowing the return address of meteorites, scientists can more easily work out how and where the building blocks of planets came together to create the solar system we see today. The downside is that it may mean researchers have an extremely biased meteorite collection that can tell only a sliver of the story. More

Planetary astronomer Bonnie Buratti remembers exactly where she was the first time she heard that Jupiter’s icy moon Europa might host life.

It was the 1980s, and Buratti was a graduate student at Cornell University studying images of the planet’s moons taken during the Voyager 1 and 2 flybys in 1979. Even in those first low-resolution snapshots, Europa was intriguing.

“It looked like a cracked egg,” she says.

Those cracks — in a snow-covered, icy shell — were probably filled with material that had welled up from below, Buratti and colleagues had shown. That meant there had to be something underneath the ice. More

Astronomers have finally found an asteroid keeping pace with Saturn in its orbit around the sun. Such objects, called Trojan asteroids, are already known for the other three giant planets.

“Saturn was sort of the odd man out, if I can call it that, because even though it’s the second most massive planet in the solar system, it didn’t have any Trojans,” says Paul Wiegert, an astronomer at the University of Western Ontario in London, Canada. Like Saturn, the new asteroid takes about 30 years to revolve but lies 60 degrees ahead of the planet in its orbit, Wiegert and colleagues report in work submitted September 29 to arXiv.org. More

For the first time, scientists have measured a long-sought global electric field in the Earth’s atmosphere. This field, called the ambipolar electric field, was predicted to exist decades ago but never detected, until now.

“That’s the big whoop,” says atmospheric scientist Glyn Collinson of NASA’s Goddard Space Flight Center in Greenbelt, Md. “It’s a whole frickin’ new planetary energy field that’s never been measured before!”

The field is weak, only 0.55 volts — about as strong as a watch battery, Collinson says. But that’s strong enough to control the shape and evolution of the upper atmosphere, features that could have implications for the suitability of our planet for life. More

A distant stellar nursery holds a clutch of newborn Jupiter-sized worlds, the tiniest of which is surrounded by a dusty disk that might someday give rise to moons. The detailed discovery, made thanks to the unparalleled sensitivity of the James Webb Space Telescope, could provide new insights into star and planetary formation, researchers report in a study in press at The Astronomical Journal.

Stars arise from enormous clouds of gas and dust when pockets of material collapse under the influence of gravity. The same process can also create smaller nonstellar objects, such as giant planets and brown dwarfs, which lack the internal pressure to fuse hydrogen into helium in their bellies (SN: 7/24/17).

In the young star cluster NGC1333, located about 1,000 light-years from Earth in the constellation Perseus, a team of astronomers found hundreds of newly formed starlike objects, including six infant worlds with masses between five and 15 times that of Jupiter. The dusty disk around the smallest world is exactly like the kind that circle baby stars and give rise to planetary systems. This dusty disk might one day turn into a pack of orbiting moons, says Adam Langeveld, an astrophysicist at Johns Hopkins University.

During a recent survey, the James Webb Space Telescope spotted six newborn Jupiter-size worlds, three of which are circled in this annotated composite image of NGC1333. The findings provide insight into the formation of both stars and planets in such regions.ESA, Webb, NASA & CSA, A. Scholz, K. Muzic, A. Langeveld, R. Jayawardhana

With nothing smaller spotted, it’s possible that he and his colleagues have found the lightest such object that can form with a disk, at least in this particular cluster. And given the parallels between how stars and planets can form, “we’re really probing the limit of the star formation process,” he says.

Future work will use JWST to look at the chemical composition of the newborn worlds and the surrounding material, potentially helping to explain what kinds of objects can form under what circumstances in this environment. More