New Horizons probe (Illustration: NASA)

It was a busy week for space news, thanks to the annual meeting of the Division of Planetary Sciences of the American Astronomical Society. Planetary scientists no doubt wore out the “Let It Go” selection on the karaoke machine, but only after dropping some exciting new knowledge about our solar system.

Pluto’s ice volcanoes

As the New Horizons probe continues to download the massive cache of data it captured as it flew past Pluto, the discoveries just keep on coming. This week, scientists released 3D maps of Pluto’s surface, including two mountains with shapes that are strikingly familiar.

“These are big mountains with a large hole in their summit, and on Earth that generally means one thing — a volcano,” said Oliver White, New Horizons postdoctoral researcher at NASA’s Ames Research Center in California.

Because it’s so cold In the outer solar system, the geology of places like Pluto is nothing like Earth’s. Pluto’s mountains are made of water ice, and its volcanoes probably erupt a partially melted slurry of ice, nitrogen, ammonia, and methane. Volcanoes are one way that a planet like Pluto can replenish its surface, paving over craters and smoothing everything out.

A cratered area of Pluto on the left, the smoother Sputnik Planum on the right. (Photo: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)

The New Horizons team also released an analysis of Pluto’s craters, revealing that the planet has some old, heavily cratered terrain; some lightly cratered “middle-aged” areas; and the bright, uncratered “heart” known as Sputnik Planum. That suggests that Pluto has been geologically active for a really long time, whether that’s thanks to ice volcanoes or other processes yet to be discovered.

Mars can’t have nice things

Last week we learned, courtesy of NASA, that Mars’s atmosphere has been gradually blasted away by the relentless solar wind. Well, we have some more bad news, Mars: You’re going to lose one of your little moons, too.

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This week, Terry Hurford of NASA’s Goddard Space Flight Center revealed that Phobos (the larger of Mars’s two moons) “has already started to fail,” based on analysis of the deep grooves that are visible on the moon’s surface.

Phobos, cracking under the strain. (Photo: NASA/JPL-Caltech/University of Arizona)

It turns out that the grooves on Phobos are being caused by tidal forces — in other words, by the pull of Mars’s gravity. Phobos isn’t a tightly packed ball of rock, either; it’s more like a loose agglomeration of dust and rubble. It’s slowly falling apart, and at some point in the next 30 to 50 million years it’ll be gone.

Yep, it’s tough being Mars. But don’t get smug, Neptune: Your largest moon, Triton, shows similar signs of fracturing on its surface and may share Phobos’s fate.

Pluto’s long-lost second cousins

Our solar system is bigger than you might think.

When most of us were in school, we learned that the solar system started with the sun and ended with Pluto. Astronomers updated their relationship status with Pluto a decade ago, because it’s really just one of the biggest of a huge assortment of icy objects in the outer solar system in a realm called the Kuiper Belt.

But even the Kuiper Belt isn’t close to the end of the solar system. Beyond it lies the the Oort cloud, made up of icy debris left over from the formation of the solar system. This is the realm of the most distant solar-system object ever spotted, as announced this week by the Carnegie Institution for Science in Washington, D.C., and the Gemini Observatory in Hawaii.

Out in the Kuiper Belt. (Photo: NASA/ESA/G. Bacon/STScI)

The object, called V774104, is 103 times farther away from the sun than Earth, three times farther away than Pluto. It’s so far away that it will be a while before astronomers can figure out its exact orbit to determine whether it’s actually part of the Oort cloud or gravitationally influenced by Neptune; the latter would, by definition, make it part of the Kuiper Belt.

Now it’s time for the astronomical conspiracy theory: There’s a chance that this newly discovered object (along with two previously known objects in the Oort cloud) may be influenced by a larger object orbiting 250 times farther away from the Sun than Earth. This object, which could be larger than Mars, would be cold and dark — but still a long-lost cousin of the planets in the inner solar system.

It’s likely there is no Planet X. But the solar system is still big and still contains many mysteries.

Winter is coming

As Earth’s Northern Hemisphere puts on the snow tires and gets ready for winter, it’s nice to know that the weather’s frightful in space, too. This week the Cassini spacecraft reported that Saturn’s moon Titan has a “massive ice cloud” forming over one of its poles. Titan is one of the few moons in the solar system with a thick atmosphere, so studying it often combines astronomy and meteorology.

Bundle up, Titan. It’s getting even colder out there.

Jason Snell is a longtime technology journalist and podcaster who blogs at Six Colors and co-hosts the space podcast Liftoff.