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.
For starters, we have three planets in the habitable zone of our own Solar System: Venus,
Earth, and Mars.
And as we know, just because liquid water can be present, that doesn’t meant that
it is present.
On Venus, the atmospheric pressure makes the world like an oven, hot enough to melt lead.
Atmosphere is the problem over on Mars too, where it’s not thick enough to trap in the
heat.
Mars is a dry, cold desert.
You wouldn’t last more than a few moments on its surface without a proper spacesuit.
Even though liquid water could exist, doesn’t mean that it does exist.
There’s another problem.
The star itself, TRAPPIST-1 is a red dwarf star, and these have a reputation for being
temperamental.
Some can produce megaflares that would scour the life off a planet like Earth, especially
considering how close they have to be for liquid water to form.
Seriously, compare the orbits of the planets at TRAPPIST-1 compared to the moons of Jupiter.
That’s how close they are.
That said, the astronomers studying TRAPPIST-1 say it’s a very quiet star.
So, maybe there’s some good news there.
Because the planets are located so close to their parent star, they’re probably tidally
locked, like the Moon is locked to the Earth.
This means they only show one face to the star.
One hemisphere of the planet is in constant sunlight, while the other hemisphere is in
permanent darkness.
I don’t know about you, but that sounds like it would make life harder.
There is one idea that will fire your imagination, though.
These planets are huddled so close together in the system they’re easy to see from each
other.
If you could stand on the surface of one world, the other planets would be visible in the
sky.
Not as points of lights, but as actual worlds, larger than the Moon.
One last thing to remember, this star is located 39 light-years away.
That’s relatively close in galactic terms, but it’s incredibly far away considering
how tough it is to get to Mars.
We have no way to travel there and study it any closer.
Even messages to and from any intelligent civilization would take a single human lifetime
to hear a reply.
We’re really only going to be able to observe these worlds from afar.
This week was historic in the search for extrasolar planets.
We still haven’t found that elusive Earth 2.0 yet, you know, Earth-sized world orbiting
a sunlike star, in the habitable zone, but it’s a collection of planets like nothing
else we’ve ever seen.
Once the James Webb Space Telescope and other big new observatories get working, they’ll
tell us even more.
More about their orbits, atmospheres, and even if they have exomoons.
We’ll get a much better sense of what star systems look like across the Milky Way, and
where we should be looking next.
This episode was a bit of an experiment.
We dropped everything to help you understand a big piece of news that broke this week.
Do you want more of this?
Let me know your thoughts in the comments.
The search for another Earth goes on.
Here’s a video where I talk about what it’s going to take to find a true Earth 2.0.