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MU69 seems to be much flatter than we thought and the Gaia space telescope can tell us where galaxies have been and, maybe, where they're going.

Host: Caitlin Hofmeister

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[ ♪ Intro ].

On New Year’s Day, the New Horizons spacecraft performed the farthest flyby ever, zooming past an object called MU69. It’s a small, frozen rock way past Neptune, and because it’s so cold, it likely hasn’t changed much in billions of years.

So scientists have been hoping it can teach us about the solar system’s early conditions. Except, we may have gotten more than we bargained for. For the last few weeks, as the first images of MU69 have trickled in, we’ve been looking at what we thought was some kind of primordial snowman… but we were wrong.

Last week, NASA released a new picture of MU69, based on images that New Horizons snapped 10 minutes after its closest approach. And after some analysis, astronomers discovered that our beloved snowman is actually more like a pair of lumpy pancakes. We’ve never seen anything quite like it, and it’s throwing astronomers for a loop.

And it wasn’t simple to get this picture of MU69. At this point in the flyby, New Horizons was looking backward into the solar system, and it saw the rock as nothing but a crescent of light. A lot like with a crescent Moon, the unlit part of its body was completely invisible.

And the lit part was so faint that the photos had to have long exposures to collect enough light to see much of anything. But that also meant those images were really blurry, which will happen when you’re taking a long-exposure picture while flying by at more than 50,000 kilometers per hour. To form this new image, astronomers stacked a bunch of blurry photos together and processed them to get a sharper image.

Then, they traced around the region where background stars were blotted out, which allowed them to outline the shape of MU69. The team found that largest lobe was extremely flat, and the smaller one looked a little more like a walnut. And that kind of throws a wrench in things, because until now, the early data coming in from MU69 have mostly confirmed our basic ideas about how the solar system formed.

The two lobes, frozen mid-collision, offered pretty solid evidence that, early on, tiny, relatively round planetesimals clumped together to form larger bodies, including the planets. But this flatness thing comes out of left field. We’ve never seen an object this shape orbiting the Sun.

The closest thing to it might be Saturn’s moon Atlas. It’s flat too, but it formed under completely different circumstances, in the middle of Saturn’s rings, so it doesn’t help us understand how MU69 came to be. So far, scientists don’t have any strong ideas about what might have flattened these rocks.

But as more data slowly cross the several billion kilometers between us and New Horizons, we’ll continue to learn more. Whatever hypotheses emerge will almost definitely shake up our ideas about the process that made MU69, and the process that likely made Earth. Objects like this can help researchers understand the past and future of our solar system, but astronomers are also interested in a lot more than that.

On a much more massive scale, they’re also decoding our galaxy’s past as a way to understand what’s in store for it. We’ve known since the 1920s that, unlike other galaxies, which are moving away from us, a number of nearby galaxies are moving toward us. They’re part of what’s called the Local Group and, eventually, the whole thing will merge with other objects to form one massive galaxy.

But until now, the details of exactly how and when that will happen have been hard to pin down. Then, last week, astronomers announced in the Astrophysical Journal that they had mapped the motion of our two largest neighbors: the Andromeda and Triangulum galaxies. Along with the Milky Way, they hold most of the mass in the Local Group, and their pasts and futures are intertwined with ours.

So studying them has given scientists the clearest picture yet of the Milky Way’s fate, and of its eventual collision with Andromeda. The researchers used data from the European Space Agency’s Gaia space telescope, which is about 1.5 million kilometers from Earth. Gaia was made to create a 3D map of stars that are mostly in our galaxy.

But it’s actually powerful enough to peek inside other nearby galaxies, too. For this study, the researchers identified thousands of individual stars in these galaxies, then collected really precise data on their positions and motions, which, by the way, is not easy to do: On the plane of the sky, any movement a few million light-years away is miniscule. But it’s worth it.

The useful thing about individual stars is that they can give us a detailed look at a galaxy’s structure and reveal how stars move around its axis. The scientists were able to use the data to trace the paths of Andromeda and Triangulum for billions of years into the past and future. And they found a few interesting things.

For one, it looks like we’re actually not poised for a head-on collision with Andromeda, as we used to think. When the two galaxies do have their run-in, it will be more of a shoulder bump, where they hit each other from the side. That doesn’t mean it will be pretty though,.

Andromeda is still headed for us at around 400,000 kilometers per hour, but it won’t be the smashup we expected. The new findings also push back the date of that fateful collision to about 4.5 billion years from now. That’s around 600 million years later than existing models.

These results show that Gaia has lots of potential for exploring beyond the galaxy. And the better we understand these neighbors, the more we can figure out about the structure and evolution of galaxies in general. Astronomy research can often work like a catapult:.

The farther we go back, the farther we can reach into the future. And from the edges of our solar system to well beyond the Milky Way, astronomers are using that strategy to make sense of the universe. Thanks for watching this episode of SciShow Space News.

And a special, spacious thanks to SR Foxley, our Patreon President of Space. Scientists are learning new things about the universe literally every week, and we wouldn’t be able to keep up with covering it without your generous support. If you want to help make SciShow high quality and free to everyone who wants it, check out

And thank you! [ ♪ Outro ].