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Duration:06:55
Uploaded:2019-07-19
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Scientists have conclusively imaged a circumplanetary disk around a distant exoplanet, and Jupiter's auroras claim the spotlight with their unique Birkeland currents.

Hosted by: Caitlin Hofmeister

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Sources:

https://iopscience.iop.org/article/10.3847/2041-8213/ab2a12
https://public.nrao.edu/news/2019-alma-circumplanetary/
https://hubblesite.org/contents/news-releases/2019/news-2019-26.html
https://www.syfy.com/syfywire/alma-reveals-a-dusty-ring-around-a-young-exoplanet-that-may-be-forming-moons

https://www.eurekalert.org/pub_releases/2019-07/uoc-acc071119.php
https://www.nature.com/articles/s41550-019-0819-7

Images:

https://public.nrao.edu/news/2019-alma-circumplanetary/#PRimage0
https://hubblesite.org/contents/media/images/2019/26/4502-Image.html?news=true
https://en.wikipedia.org/wiki/File:3-ALMA-antennas-interferometry.jpg
https://hubblesite.org/contents/media/images/2019/26/4488-Image.html?news=true

https://en.wikipedia.org/wiki/File:Hubble_Captures_Vivid_Auroras_in_Jupiter%27s_Atmosphere.jpg
https://svs.gsfc.nasa.gov/13007
https://vimeo.com/205561528
https://www.jpl.nasa.gov/news/news.php?release=2017-236
https://svs.gsfc.nasa.gov/12865
https://commons.wikimedia.org/wiki/File:Schematic-of-combined-FACs-and-ionospheric-current-systems.png
https://www.missionjuno.swri.edu/media-gallery/magnetosphere
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 offers more than 2400 documentaries and nonfiction titles, including some exclusive originals. And it’s a great place to learn more about space. Like, there’s a series called Destination: Pluto about a mission we’ve talked about a lot: the New Horizons mission to Pluto.

It tells you more about why Pluto is so important and even has interviews with the team who made the spacecraft. If you want to check it out, you can get unlimited access to CuriosityStream starting at just $2.99 per month. And for SciShow Space viewers, the first 31 days are totally free if you sign up at curiositystream.com/space and use the promo code “space.” We hope you learn something new! [♪ OUTRO].