Name: 宇宙人は地球を見ることができるのか？ (Would Aliens Be Able to See Earth?)
Uploaded: 2021-01-14T10:41:04.000Z
Duration: 5 min 34 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

Scientists are always keeping an eye out for extraterrestrial life, and finding friendly,

But if we ever want a long-distance relationship with aliens, finding them is only half the battle.

And according to a paper published online last month in the Monthly Notices of the Royal

Astronomical Society, that might not be so easy.

The researchers based their calculations on what someone on another planet would see if

they tried to detect planets in our solar system using the main technique we use to

We've found more than three and a half thousand exoplanets since the first discoveries back

Scientists have a few different ways of detecting them, but by far the most successful is the transit method:

They watch to see if a star seems to get dimmer periodically, which can mean there's something

regularly passing in front of it. Like a planet.

It's such a simple technique that we've used transits to find three-quarters of the

exoplanets we've discovered so far, but it has its limits — mainly, we can only

use transits to find planets that pass between us and their stars.

There are lots of exoplanets out there that we just can't detect using this method,

because their orbits don't line up right.

That limitation would also apply for any aliens using the transit method to look for planets

They'd only be able to see us if they were in just the right place to spot Earth passing

So, the paper's authors used the size and locations of our Solar System's planets

to calculate where you'd be able to see them transit the Sun, and what they found

From any random point in space, intelligent life would only have about a 2.5% chance of

being able to see any of the planets in our solar system transit the Sun.

And there's only about a 0.5% chance they'd be able to see Earth, specifically.

They'd have around a 0.2% chance of being able to see two planets, and a 0.02% of seeing three.

But the authors didn't just do their calculations and end their paper with a “Forever Alone” meme.

They went through all the known exoplanets and found about 65 in the right place to see

one of the planets in our solar system, including 9 that could see Earth.

And based on what we know about how often different kinds of exoplanets form, they calculated

that there might be around ten nearby, Earth-like planets that we can't see because they're

at the wrong angle, but where you could see Earth transit the Sun just fine.

Of course, we don't actually know if there's extraterrestrial life out there, let alone

intelligent life that knows how to use the transit method to detect planets around other stars.

But if there is another civilization out there wondering if it's alone in the universe,

at least now we know a little more about whether they'd be able to see us.

Meanwhile, we're also learning more about how galaxies work.

There's still a lot that astronomers don't quite understand about how galaxies form,

and one mystery is how they get their magnetic fields.

But in a paper published this week in Nature Astronomy, researchers reported the best-ever

measurements of a distant galaxy's magnetic field, which are helping chip away at some

Magnetic fields are really important for helping galaxies keep in order: they help gravity

maintain the galaxy's overall structure, and they help gas clouds collapse to form stars.

It's pretty hard to study magnetic fields from a distance, though, because they tend

to be pretty weak, and we can't see them directly like we can see light.

The problem is, distant galaxies are exactly the ones we need to study to figure out how

They're so far away that their light has taken billions of years to get to Earth, so

they're like a window to the early universe.

Astronomers usually measure a galaxy's magnetic field by studying how it affects the light

The technique works great for mapping nearby galaxies, and even some distant galaxies with

But it doesn't work as well for distant galaxies with plain-old average magnetic fields,

and without knowing more about average galaxies, we can't really understand how most galaxies evolved.

So the authors of this new study decided to see how light from a really bright, distant

galaxy — about 7.9 billion light-years away — was affected by the magnetic field in

a slightly closer, more average galaxy, about 4.6 billion light-years away.

All that bright light made smaller effects from the closer galaxy's magnetic field

a lot easier to see, and because of the way these two galaxies were lined up with Earth,

the team was able to measure the magnetic field in the closer galaxy really precisely.

That gave them our best picture yet of what galaxies' magnetic fields looked like in

For one thing, this galaxy's magnetic field was about as strong as the fields in today's

galaxies, which tells us that galactic magnetic fields probably haven't changed too much

They also found the most distant evidence yet for one of our best explanations of why

galaxies have magnetic fields in the first place — a dynamo, swirling gas and intense

cosmic rays that sustain the galaxy's magnetic field by enhancing the smaller fields from

So, thanks to a couple of galaxies billions of light-years away, we now know a little

bit more about how the universe around us came to be.

Thanks for watching this episode of SciShow Space News, and thank you especially to all

of our patrons on Patreon who help make this show possible.

If you want to help us keep making episodes like this, you can go to patreon.com/scishow.

And if you just want to help us out by watching and sharing, that is also great.