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It’s been more than 20 years since astronomers discovered the first planet orbiting a star beyond our own. And today, there’s a catalog of more than 3700 confirmed exoplanets, along with thousands more unconfirmed candidates.

But now, we might have found the very first moon beyond our solar system, or an exomoon. Last week, Science Advances published the first quote-unquote “compelling evidence” of a huge,. Neptune-sized exomoon 8,000 light-years away.

In 2017, data from the Kepler Space Telescope seemed to contain hints that an exomoon might be out there. The data revealed that a body the size of a gas giant was orbiting a larger body called Kepler-1625b. Now, two astronomers from Columbia University have used the even-stronger.

Hubble Space Telescope to further explore the system. And from what they saw, it looks like that exomoon signature isn’t some error in the data. In the new study, the team used the transit method to study 1625b.

In other words, they analyzed the light coming from its star and how it dims as the planet passes between the star and us. The weird thing was, about 3.5 hours after the planet’s transit ended, there was a smaller dip in brightness. That suggests the planet has a moon trailing it.

To the disappointment of space nerds everywhere (including us) the team ran out of observation time before the potential moon had finished its own transit. So they don’t have a full set of data to analyze. The good news is, there is a little more data that supports the planet having a natural satellite:.

The planet’s transit started over an hour earlier than was predicted. That could happen if it had a moon tugging on it and changing the system’s center of gravity. So far, all this evidence suggests this moon, if it exists, is comparable in mass and size to Neptune.

By our standards, that’s huge. But since the planet is around the same size as Jupiter and a few times more massive, it makes sense. Then again, these properties aren’t based on the strongest models, so there’s still some uncertainty.

It could be that our data is a bit off and that there isn’t a moon at all. Instead, there could be a second planet in the system that’s responsible, although there hasn’t been any evidence of that so far. It’s also possible that 1625b could just have a longer orbital period than we think.

Or it could be orbiting at such a distance or angle that it’s not transiting every time we look at it, which could be why our predictions were off this time. Right now, the authors of this paper confess this first exomoon has to survive years of scrutiny and follow-up before its existence can be confirmed. But if it does end up being a moon beyond our solar system, it will be a really important target to continue studying.

For example, since it’s likely much, much larger than any moon in our system, it opens the question of how planetary systems form and evolve. And the moon’s origins at the moment are a total mystery. Like, was it captured, or did it form alongside its partner?

At this point, we can only guess. In other moon news, a study published online this week in Nature Geoscience predicts a decent chunk of Jupiter’s moon Europa might be covered in giant ice blades! Officially, these blades are called penitentes.

They’re formed when large chunks of frozen water heat up and sublimate, turning directly from a solid into a gas. On Earth, we see this happen in places like the top of the Andes Mountains. But we’ve also seen evidence of these blades on Pluto.

For penitentes to form, the environment has to be super dry and cold, the air has to be really still, and the sunlight has to hit the ice at just the right angle and for long enough periods of time. Then, the Sun’s radiation causes heaps of water molecules to sublimate, carving deep depressions into the surface and turning everything really spiky. In other words, the penitentes don’t grow up like stalagmites do they’re leftovers!

Eventually, penitentes smooth out or break apart, either from geologic activity beneath the surface or space debris smashing into them from above. But the amount of time that takes can vary. To learn more about Europa, astronomers wanted to determine the likelihood, location, and size of penitentes.

So they created a model. It took into account things like how Europa is tilted toward the Sun, its range of temperatures, and the reflectivity of its surface. They also needed to estimate how often space debris would crash into.

Europa’s surface, which would smooth out its features. According to their model, water could sublimate faster than erosion could smooth things out at latitudes below 23° or so. That means, for a large band around Europa’s equator, we’d likely see a healthy population of penitentes.

The team also calculated that, over 50 million years which is the average age of Europa’s surface the blades could get up to 15 meters tall. That’s three times taller than what we usually see on Earth. Of course, all their stats are averages, and don’t take into account local geologic features, or exactly how impurities in the ice will play a role.

So there may be more to the story. Unfortunately, our technology near Europa doesn’t have the proper resolution to find photographic evidence of this spiky surface. But there is both ground-based radar and thermal data from the 1990s Galileo probe that suggests penitentes could be there.

Studies like this are cool, but they’re about more than just uncovering giant ice spikes on a far-flung moon. To scientists and engineers, this kind of information is really important to know when planning a future lander mission to Europa. The moon is one of a few that scientists are almost definitely sure has a liquid water ocean beneath its surface.

And although there aren’t any landers officially on the docket right now, we’ll need all the information we can get when we are ready to go. Thanks for watching this episode of SciShow Space News! And thanks especially to our Patrons on Patreon.

The things beyond our planet are beautiful and fascinating, and we love getting to explore them with you. [♩OUTRO].