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Seven New Earth Sized Worlds Discovered?

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Team: Fraser Cain – @fcain / frasercain@gmail.com
Karla Thompson – @karlaii
Chad Weber – weber.chad@gmail.com

I’ve been doing this space news thing for almost 18 years now, so I’m on a lot of mailing lists for the media. Every few weeks, there’s a big press conference announced. Then the rumor mill begins, blows the news way out of proportion and everyone’s expectations are driven sky high.

So when NASA queued up a press conference this week, to make some announcement about extrasolar planets, I was excited, but realistic. I’ve been burned before.

Well, here we are, right after the announcement, and let me tell you. This is gigantic news, one of the most exciting discoveries in the history of the search for planets orbiting other stars. And in the search for life.

So, here’s the news: A team of astronomers have discovered an extrasolar planetary system where there are seven Earth-sized worlds orbiting a red-dwarf star. Seven! Not only that, and this is the best part, three of those worlds are orbiting within the star’s habitable zone, which means that there could be liquid water on the surface of three of these planets.

Suddenly, the chances for finding life in the Universe went way way up.

The star is known as TRAPPIST-1, and astronomers have known it’s had planets for a couple of years now. In fact, the name “TRAPPIST” is short for the Transiting Planets and Planetesimals Small Telescope, which is the telescope in La Silla, Chile which discovered them in the first place.

It’s also the Belgian word for a kind of beer, and I’m almost certain this overlap is intentional.

Transiting should tell you what technique they’re using. They use the telescope to watch the light coming from the star over a long period of time. As a planet, or in this case 7 planets, pass in front of the star from our perspective, the total light dims a tiny little bit.

The group of astronomers working with TRAPPIST-1 originally announced that they’d found planets around the star back in May 2016. The news on Wednesday is that they found an additional 4 planets, and figured out that some of these are in the habitable zone.

The main thing to remember is that this is a red dwarf star, not a main sequence star like our own Sun. It only has about 8% the mass of the Sun, which is right at the very lower limit of what’s even possible for stellar fusion. Any smaller and it wouldn’t even be a star.

It’s about 500 million years old, which is relatively young for a star compared to our own Sun’s 4.5 billion years. That said, it uses its fuel so slowly, it’ll remain in the main sequence for another 4-5 trillion years, long after the Sun is dead and gone.

With this kind of feeble light, the 7 planets are huddled up close to their star.

What kinds of worlds are we talking about? They’re pretty extreme.

Astronomers designate extrasolar planets by letters, starting with b. From the closest to the most distant.

First up, the 3 planets which are too close to the star to have liquid water. TRAPPIST-1b is almost exactly the same size as the Earth and orbits the star every 1.5 days. Days!

1c is close to Earth-sized too, and orbits every 2.4 days. 1d is smaller, only 77% our planet’s size, and takes 4 days to orbit.

Now, the planets we’re most interested in start with 1e, the innermost of the habitable zone planets. It‘s only 91% the size of the Earth, so it’s a little smaller than Venus, but it receives almost exactly the same amount of radiation from its star that we get here on Earth. It takes just over 6 days to orbit the star once.

TRAPPIST-1f comes next, the same size as the Earth and it has a 9-day orbit, getting about as much starlight as Mars does.

The outermost habitable zone planet is 1g. It’s 13% bigger than Earth, and takes 12.4 days to complete an orbit around the star. Compared to our Solar System, it would be found orbiting somewhere between Mars and the Asteroid Belt. Probably pretty chilly.

After that is 1h. It’s 76% the size of Earth, and takes 20+ days to orbit the star. It’s well outside the habitable zone of the star, and any water on the surface would be frozen.

That said, the astronomers think that the atmospheric composition makes a big difference, so maybe more of them could have liquid water.

I know your mind is buzzing right now, 3 Earth-sized worlds orbiting within the habitable zone of another star. There could be life there!

Well maybe, but probably not. There are a few reasons why this system isn’t the greatest place to go searching for life.

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