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There’s a saying in astronomy  that telescopes are time machines. It’s based on the fact that light from  distant objects can take a while to reach us.

So when we detect that light with telescopes,   we’re really seeing how objects used to  look, rather than what they look like now. But it turns out there’s  another way to probe the past,   and that’s by studying what are  basically cosmic graveyards. Or, to get more specific: Last week  in the journal Nature Astronomy,   researchers proposed a way to study  the composition of ancient planets,   by hunting down the vaporized  pieces of them stolen by dead stars.

What? Ok…. When stars run out of fuel, their cores  collapse under the power of their own gravity,   crushing the remaining matter into  a small, incredibly dense package.

The outcome can look different  depending on the star. But for   stars similar in mass to our Sun, the  resulting object is a white dwarf. Even though a white dwarf is small, its  gravitational pull can still rip apart   and pull in any matter that strays too close.  So on their own, they’re fascinating object.

But while studying the light from a  sample of over a thousand white dwarfs,   the researchers behind this new study noticed that  one of them had an especially weird light signal. Upon further analysis, that weirdness  turned out to from be the element lithium   in the star’s photosphere — the  closest thing a star has to a surface. Now, lithium isn’t very abundant in most stars.

But you know where you can find it? The  crusts of rocky planets, like Earth. To figure out what was going on, the team  looked at over 30,000 more white dwarfs,   and found the telltale signs of lithium   in three more targets — plus one star that  had another element common to planet crusts.

Then, they looked at the amount of  lithium, and compared that against   the ratio of elements found in other  objects like the Sun and meteorites. And ultimately, the team concluded that  they were looking at vaporized crust   from destroyed planets, hiding  in white dwarf photospheres. Now, this isn’t the first time we’ve detected   planet guts in a white dwarf.

We’ve found  pieces from planets’ inner layers before. But this is the first definitive  time we’ve found crust. The researchers think they were able to  detect this material in these white dwarfs,   and not others, because the stars are super old  — like, they formed up to 10 billion years ago.

So they’re cooler, and their light is  dimmer and less overwhelming than what   you see in younger white dwarfs. That makes it  easier to detect the presence of any debris. Now that they know what to look for,  astronomers can go back into the records   of other white dwarfs and hunt for the  remnant signals of disintegrated planets.

And besides being incredibly  hardcore, that will open up a   new way of figuring out exactly what rocky  planets were made of in these old systems,   how they formed, and how  abundant rocky planets even were. In other news this week, scientists have confirmed   that they’ve found the farthest  known object in the solar system!   And it was officially acknowledged by  the International Astronomical Union. The IAU is the worldwide organization  responsible for naming various bodies in space,   among other things.

They are currently  calling this object 2018 AG37. After we learn more about it, it will get a  name that’s easier to remember, but for now,   it’s better known by its  unofficial nickname: Farfarout. Farfarout.

Researchers announced they’d  found this object in 2019,   while they were hunting for  potential big planets beyond Neptune. They spotted it in data collected by the Subaru  telescope in Hawai’i. And although they suspected   it was pretty far away, they couldn’t tell just  how far based on their limited observations.

So, they started following up on it. The tricky thing is, because this thing is so, so  far, it takes a long time to go around the Sun. And it took years for its  position in the sky to change   enough for us to figure out the shape  of its orbit, and its current distance.

But, by following up with the Gemini  North telescope in Hawai'i and the  . Magellan Telescopes in Chile, Farfarout’s  discoverers were able to pin it all down. For one, they calculated that it’s  currently 132 astronomical units away.

That’s 132 times farther away  from the Sun than Earth is,   and about three times farther  than Pluto is on average. For comparison, the previous record-holder,  which was found by the same team and nicknamed  . Farout, is about 124 astronomical units away.

Based on how much sunlight it  reflects and how far away it is,   the team also estimated that it’s about 400  kilometers across, which actually makes it the   size of some dwarf planets. Although we’ll need  to know more about it before it gets that title. Either way, finding record-breaking objects  is always a big milestone for science,   but Farfarout also has a bit of a mystery to it.

Because here’s the thing: its  orbit is super elliptical. Over the course of its thousand-year  orbit, it actually gets closer to the Sun   than Neptune does, and will go as  far out as 175 astronomical units. The fact that it crosses Neptune’s orbit means the   planet likely had a hand in flinging  Farfarout into such a wonky orbit.

And by studying this new object more closely,   we can get a hint at what happened in the outer  reaches of our solar system, long long ago. So, this isn’t just an interesting entry into  the record books: Like with those white dwarfs,  . Farfarout might also be a key to understanding  what happened in the universe in the distant past.

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