The 7 Earth-sized Worlds of TRAPPIST-1 | SFN #196

NASA announces the discovery of seven Earth-sized worlds in orbit around the star known as TRAPPIST-1, a star that is cool enough that liquid water may be present. But can life really exist on these worlds?

Published by Tony Darnell on 24th Feb, 2017

Hello Space Fans and welcome to another edition of Space Fan News. By now, I’m sure you’ve all heard about NASA’s big announcement this week about the seven Earth-sized worlds in orbit around the star known as TRAPPIST-1, a star that is cool enough that liquid water may be present. But can life really exist on these worlds? I’ll give you my thoughts.

This week, NASA announced the discovery of seven Earth-sized worlds around the cool, M-class red dwarf star known as TRAPPIST-1, some 40 light-years away. This star got its name because it was discovered using the Transiting Planets and Planetesimals Small Telescope - or TRAPPIST - in Chile.

And back in May 2016 they had announced they had discovered three planets around this star and they said back then that both Hubble, Kepler and Spitzer Space Telescopes would be taking a better look.

Well this week, assisted by several ground-based telescopes, including the European Southern Observatory's Very Large Telescope, the Spitzer Space Telescope confirmed the existence of two of these planets and discovered five more, increasing the number of known planets in the system to seven.

All of these planets were detected by the transit method, something you guys know all about by now, which is measuring tiny dips in brightness as the planet moves between us and the star the planet is orbiting.

Using Spitzer data, the team precisely measured the sizes of the seven planets and developed first estimates of the masses of six of them, which allowed their density to be estimated.

Based on those densities, astronomers say all of the TRAPPIST-1 planets are likely to be rocky. And further observations will not only help determine whether they have atmospheres, but also possibly reveal whether any could have liquid water on their surfaces. The mass of the seventh and farthest exoplanet has not yet been estimated – scientists believe it could be an icy, "snowball-like" world, but again, further observations and all that.

Astronomers like to ensure their job security just like everyone else.

What’s cool is that these seven planets are the first Earth-sized ones that have been found orbiting this kind of star. And boy is this system weird.

All seven planets are crammed really close to the star, they would all fit inside the orbit of Mars. In this case though being jammed in there is a good thing because TRAPPIST-1 is an ultra-cool dwarf, which means as Red Dwarf stars go, they not only do they get to sit at the cool kids table in the cafeteria, the coolness of this star makes liquid water possible on any one of them.

Another weirdness is that the planets are all pretty close to each other. NASA is saying that if a person was standing on one of the planet’s surface, they could gaze up and potentially see geological features or clouds of the others, which would sometimes appear larger than the moon in Earth's sky.

And yet another weirdness (and don’t ask me know something can be so weird and cool at the same time, my experience with being weird is that I never got called cool), but another weirdness is that all of these planets are probably tidally-locked to the star, meaning one side of the planet always faces towards the star and the other out into space away from it.

This would mean that if any of these planets had an atmosphere, they would have weather patterns totally unlike those on Earth, such as strong winds blowing from the day side to the night side, and extreme temperature changes. Just all around weather weirdness too.

OK, so in summary, here’s what we know: thanks to the transit method we’ve found there are seven, Earth-sized worlds orbiting very close to an ultra cool dwarf; these planets are probably rocky based on initial estimates of their density; they are tidally locked to their star; and they are close enough to this cool star that if they have atmospheres and if they have water, well, then that water could be liquid.

And we know this thanks to the Spitzer Space Telescope, an infrared observatory that follows behind the Earth as it travels around the Sun, and it stared at TRAPPIST-1 nearly continuously for 500 hours. Engineers optimized Spitzer’s ability to observe transiting planets during Spitzer’s “warm mission,” which began after the spacecraft’s coolant ran out as planned after the first five years of operations.

What we don’t know can fill stadium: We don’t know if these planets have atmospheres, we’ll need more detailed observations from Hubble (coming up later this year) and Kepler, which is now operating as K2, and those observations will help set the observing program for the 500 pound infrared gorilla known as the James Webb Space Telescope which will launch in October of 2018.

JWST will be able to directly detect and measure any atmospheres these worlds may have and not only that, it will tell us what they’re made of.

So that was the announcement and apparently it broke all records in NASA’s social media empire. People were hungry to know more and they held a press conference and pulled out all the stops in making this announcement. In some ways, NASA reminds me of a certain president, they loved to be told how great they are.

Anyway, I wanted to talk briefly about these red dwarf stars and the possibility that they may be the best place to look for life in the universe. If you haven’t see it yet, go see the video I made about these called The Embers of Creation. These stars have a lot going for them in terms of harboring life. But astronomers are torn in two basic camps about how great they are for harboring life. Camp one says they’re the place to look for life in the universe and camp two says notsomuch.

Red Dwarf stars are the most common stars in the universe. They out number all other stars by a factor three to 1 and comprise 75% of the stars in the Milky Way Galaxy. They also live a really long time, because they are so cool, they can shine for trillions of years, so all of the red dwarf stars that have ever been born, are still around unless they got sucked into a black hole or died in a supernova, or merged with another star.

And Camp One of astronomers says this works in favor of life being found around them. Because they last so long, they reason, and are relatively stable after they’ve been around for about a billion years, this may mean that life can take its time forming on any worlds around these stars and probably have a great chance of surviving. They are pretty stable once they get going.

And that’s where camp two says not so fast. Red dwarf stars have temper tantrums when they’re young. These stars are extremely active in their early years—shooting off potentially lethal flares and bursts of radiation that could wipe them out.

And these tantrums would last a really long time, up to a billion years after they are born. No one is quite sure how old TRAPPIST-1 is, but scientists believe it is at least 500 million years old, or about one-tenth the age of our sun, which is four and a half billion years old.

Another problem that camp two says makes life an uphill battle on these stars is the location of the habitable zone. The “habitable zone” around such stars is very close. All seven of the Earth-sized planets crowd so close to their star that they complete a single orbit—their “year”—in a matter of days, 1.5 days for the nearest planet and 20 days for the farthest.

This means they’re tidally locked and would have some really bizarre weather.

But that’s not all, a recent study also showed that the flaring tempers of young red dwarfs, with their bursts of high-energy X-rays and ultraviolet emissions, could actually strip oxygen from the atmospheres, sterilizing the huddling planets in orbit.

These flares could even strip the atmosphere entirely.

But wait, there’s more! In yet another potentially sterilizing effect, even if M-dwarf planets managed to hold on to their atmospheres, all this high-energy radiation could trigger a runaway greenhouse effect.

But camp one says hold on a minute, don’t drop that mic, things may not be all that bad! Life is very tenacious and we’ve seen evidence on Earth that life can life and even thrive in some pretty crappy places, so maybe life can just deal with it.

Maybe, Camp One optimists say, maybe the atmosphere can recover, and everything is just fine. We do have evidence of life adapting to outbursts of stellar radiation.

You can have regular events, but life is used to this, Camp one says. It just deals with it. We certainly see life on Earth capable of hibernating for very extended periods of time. We see that life goes into a state where it shuts down, sometimes for years or decades. So we shouldn’t, probably, rule it out, but we should put a lot of effort into studying whether this is a place where we think life could thrive.

I think that whether Camp One or Camp Two is correct, comes down to the question of how common life is in the universe. You’ve heard me say many times, the burning question I have is, ‘Is life arising from primordial soups easy or hard?’

If it’s a hard thing to do then I think Camp Two has got it right and red dwarf stars are too violent and will probably fry any life that tries to form there.

But if it’s easy, then Camp One has a point. And I believe we’ll find it on a lot more kinds of stars than just red dwarfs, some really harsh and bizarre ones, but red dwarfs will without a doubt be the best place to start looking.

Well, that’s it for this week Space Fans, thanks SFN Patreon Patrons, you’re making this show possible, thanks to all of you for watching, and as always keep looking up!


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