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A Tasty Trove of Exoplanets at TRAPPIST-1

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 Astronomy   |   Science
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A baker’s half-dozen of Earth-size worlds is orbiting a (relatively) nearby star—and some could be habitable

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TRANSCRIPT:
There's big news this week from 40 light years away, a star system called TRAPPIST-1. There's something happening there that no one has ever seen before.

I'm Mike Lemonick. And I'm Lee Billings. And we're here to talk about exoplanets, one of our favorite subjects. So when exoplanets were first discovered 20 years ago, they were mostly gaseous giants like Jupiter, which is interesting but it's not a place where you could have life. There's just no solid surface to stand on. We've been looking and looking for solid rocky planets like Earth ever since, and we've found a lot of them but there's a new announcement that is probably the most exciting one we've heard yet.

Very exciting. We've found a couple, haven't we?

There's not just one Earth-like planet that we're talking about. Earth-sized planet. Not two. Not three. Not five. Seven orbiting one single star, all of them about the size of Earth.

That's pretty yummy.

That's pretty yummy. You can put them down. So Lee, tell us how they found these planets.

Yeah, so it's pretty interesting. What they did to actually find them was something called the transit technique, and what that means is as seen from Earth, they essentially cross the face of their star in their orbit. And that casts a shadow towards us here that we can see as a little dimming of the star. We measure the dimming of the star, the size of the shadow, and thus the size of the planet.

Ok, but size alone is, I mean size matters, but size alone is not the only thing. You want to know that density, you want to know if it's rocky like the Earth. I understand that they have determined that all of these planets are probably rocky. To find that out, you have to know their density. Right? And so we find that out by looking at them as they orbit the star. And as they do that their gravity pulls on each other. Their orbits speed up and slow down. And by measuring that we can tell how much mass each of them has. And if you have the mass and you've got the volume, you can calculate the density. And it looks like the density is probably very similar to Earth. These are probably made of rock.

Which is pretty nifty.

It's pretty nifty. But it's not enough to show that they are habitable. They also have to be at the right distance from this small cool star to allow water to be in liquid form. And again, it's pretty amazing because,

Well, three of them are in this habitable zone, and that's kind of like Venus, Earth, and Mars are in the habitable zone here in our solar system, of course only one of those planets is habitable, ours. And here there's also three planets in this habitable zone around this star that's about 40 light years away. It's a much smaller star than the Sun. It's a little tiny red dwarf, it's called. And again, they are all huddled around it like a campfire.

Right, but in order to know whether there's actually the right conditions for life, it doesn't just have to be the right temperature, you have to know what gasses are in the atmosphere. And we actually have a way that we'll soon be able to do that.

That's right. In 2018, just next year folks, let's hope, NASA is going to be launching its James Webb Space Telescope, a giant piece of kit that's going to be about one and a half million kilometers out there beyond the orbit of the moon, and it's going to be able to look at these planets as they transit across the face of the star.

Yeah, and so what happens is if you look at the glaze on this little donut hole, that little thin glaze, the telescope will be able to watch the star light penetrating through the atmosphere, that thin atmosphere, and actually measure the gasses that are inside. So we don't have long to wait before we find out possibly whether these things are actually habitable.

And even though they may not be habitable, they are certainly edible. I'm Lee Billings.

I'm, excuse me, Mike Lemonick, please subscribe to Scientific American's YouTube channel.

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