Thanks to CuriosityStream for supporting
this episode of SciShow Space! Go to CuriosityStream.com/Space to learn more. [♪ 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. This episode of SciShow Space News is brought to you by CuriosityStream. It’s a subscription streaming service that
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