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  • [♪ INTRO]

  • Every now and then, astronomers give us an image of space

  • that just sort of makes our jaws drop.

  • And another one of those images was published

  • last week in the Astrophysical Journal Letters.

  • This is an image of a star about 370 light-years away.

  • See that little spot on the right edge of the disk?

  • That's a new, growing exoplanet.

  • And hiding in the light area around it

  • is something scientists have never

  • conclusively imaged before: a circumplanetary disk.

  • This is the cloud of stuff that the planet is

  • pulling from in order to grow, and someday,

  • if it hasn't already, the leftover material in it

  • will likely collapse to form moons.

  • The fact that we can see this from

  • trillions of kilometers away is mind-blowing,

  • but it also has a lot to teach us about

  • how planets and moons form.

  • This star is dubbed PDS 70.

  • It's about 5 million years young, and it has

  • at least two Jupiter-sized planets,

  • the second of which was announced just last month.

  • The first planet we found orbits about as far away

  • as Uranus is from our Sun, and this new,

  • second planet is about where Neptune would be.

  • It's called PDS 70 c, and it's the planet

  • that's been causing all the excitement.

  • Initially, though, scientists weren't just focusing on this world.

  • Instead, they were trying to study both planets,

  • along with the disk of stuff they formed from.

  • To do that, they re-analyzed some data taken by

  • a suite of Chilean telescopes called ALMA.

  • And they found something pretty amazing.

  • There was a noticeable clump of stuff

  • right where PDS 70 c is located.

  • And the signal was brighter than astronomers expected.

  • Combining that observation with both optical

  • and infrared data from other telescopes, the team concluded

  • there must be a circumplanetary disk around PDS 70 c.

  • Now, although this image does look pretty clear,

  • it's important to know that it doesn't actually show the disk itself.

  • The disk is too small and too far away,

  • so this picture just shows the general region around it.

  • But astronomers are really good at pulling information

  • out of smudgy images, which is why they're so confident

  • that the disk is actually there,

  • and why they can say they've conclusively imaged it.

  • Regardless, this was awesome news

  • partly because it can teach us about the planet.

  • For example, using some assumptions based on

  • current planetary formation models,

  • astronomers were able to estimate the amount of dust in the disk.

  • It's between 0.2 and 0.4 percent the mass of Earth.

  • Also, one data point suggests that hydrogen gas

  • is still falling from the disk onto the planet,

  • which means it's not done growing!

  • Then there's the whole moon thing.

  • Because some of that disk material won't join the planet:

  • If it hasn't already, it'll clump together into a multi-moon system,

  • like those we see around Jupiter and the other gas giants.

  • Most of the moons will be potato-shaped,

  • but we could also get a small spherical body or two.

  • There's a lot to unpack here, but one of the best parts

  • is that this image isn't only important for

  • understanding this one specific planet:

  • It'll also help us learn more about

  • how solar systems form in general.

  • Because, maybe surprisingly, this isn't something we totally understand yet.

  • Collecting more data about PDS 70 c will help teach us

  • how gas and dust collect around large planets in their early years,

  • and how circumplanetary disks interact with the disks around stars.

  • This information might even help us understand our own solar system,

  • since we have some big gas giants of our own.

  • Speaking of, not all astronomers are studying Jupiter-like planets:

  • Some researchers are studying the real deal.

  • Understanding Jupiter can teach us

  • why our solar system looks the way it does.

  • But also, studying this planet is cool in its own right.

  • And last week in Nature Astronomy,

  • the world learned something new about its auroras.

  • According to a new study, these light shows

  • aren't just more intense than Earth's,

  • they're also powered very differently.

  • Jupiter is the fastest-spinning planet in our solar system,

  • making one rotation about every ten Earth hours.

  • That means its magnetic field rotates really fast,

  • and it generates a force that actually steals

  • charged sulfur compounds off of its closest spherical moon, Io.

  • When charged particles move, they generate a current.

  • And this electric current is kind of a big deal on Jupiter.

  • It directs electrons toward the planet's upper atmosphere,

  • and those electrons interact with

  • atmospheric particles and make a pretty UV aurora.

  • Generally speaking, this is about the same way

  • auroras form here on Earth, although our charged particles

  • come mostly from the Sun and not from the Moon.

  • But it turns out that the electric currents around Jupiter

  • are different than the ones here at home.

  • Scientists discovered this by studying something called Birkeland currents.

  • These are electric currents that flow

  • along a planet's magnetic field lines.

  • They connect the outer regions of the magnetic field

  • with part of the upper atmosphere,

  • and they move both towards and away from the planet's poles.

  • Both Earth and Jupiter have them, and on Earth,

  • you can sort of visualize them as two concentric sheets

  • carrying a direct current that flows in one direction.

  • Birkeland currents play a big role in Earth and

  • Jupiter's auroras, so it makes sense that

  • scientists would want to learn more about them.

  • Specifically, when Birkeland currents carry

  • newly-arrived charged particles, they cause

  • perturbations in a planet's magnetic field.

  • And recently, astronomers were able to measure those

  • perturbations around Jupiter using NASA's Juno spacecraft.

  • In this new study, they calculated the strength of the currents around Jupiter.

  • And they found a total electric current of anywhere from

  • 6 million to 91 million amperes depending on the pole and the time of year.

  • Compared to Earth's 2-5 million amperes from its Birkeland currents,

  • that's a lot, but it actually isn't as strong as models predicted.

  • And that's important.

  • Because originally, those models were based on

  • how Birkeland currents work on Earth.

  • They assumed things were the same on Jupiter,

  • so we could just extrapolate what we see here

  • to the planet down the block.

  • So if those models don't match, it must mean

  • something different is happening inside Jupiter to cause its auroras.

  • That something, the team hypothesizes,

  • is lots of small areas of turbulence, basically,

  • charged particles zooming around that create not direct currents,

  • but alternating currents that occasionally change direction.

  • So instead of current sheets, there's like a bunch of filaments.

  • That would cause weaker measured perturbations,

  • but if you had enough of them,

  • they would generate the most powerful auroras in the solar system.

  • So this is yet another example of how we can't always use Earth

  • as a template when trying to study the universe.

  • We have to keep exploring the diversity that's out there,

  • from giants like Jupiter to distant potential exomoons.

  • Only then will we be able to put together a big,

  • accurate picture of space.

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  • [♪ OUTRO]

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