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{♫Intro♫}
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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