Ode to 7 orbs

Wake up now people, I’ve got some big news!
You won’t want to miss this. You don’t want to snooze.
We just found some planets while we were stargazing
Gather ’round, listen up. These ones are amazing!

Three planets in the TRAPPIST-1 system passing in front of their star (although we only detect the dips in brightness). The star’s orangy color is realistic. Credit: Franck Selsis.

And it’s not just one new planet. There are seven!
All orbiting one star up there in the heavens.
(With seven planets it still goes to eleven…)
The thing ‘bout this system that just makes us squeal,
All seven are Earth-sized. Now, that’s a big deal!
And four of those planets could have the conditions
For liquid water! (based on their positions).

“How did you find these new planets?” you ask
Well, let me first say it was no easy task
To start off, we made a long list of stars.
Then,
We measured their brightness again and again

Most of the stars just looked awfully boring
They stayed the same brightness. They weren’t worth exploring.
The ones we were looking for had little blips
Their brightness stayed constant except for small dips

transit_anim — The dip in a star’s brightness when a planet transits its star. Credit H. Deeg

Each dip is a planet that, just as it passes
In front of the star, blocks some light from our glasses
The brightness we measure goes blip every time
The planet goes once around. Then it re-aligns.
(Another way that you can think of the dips:
Each blip is like a single tiny eclipse)

Armed with the star’s brightness, we measured and figured
How big are the planets and how they’re configured.

This new star with planets is called TRAPPIST-1
It’s not a star that is at all like the Sun
It’s much much much smaller, and also less hot
Two thousand times fainter. (Now that is a lot).
An “ultracool dwarf” star they call it. And hey,
It’s just about 40-odd light years away.

The planets have letters for names. Now, you see,
From outside to in it’s h, g, f, e, d,
And, yes, as you guessed, after that, c and b
(The first one’s called b. There is no planet a.
The “a” is reserved for the star, by the way).

Comparison of the relative sizes of the planets’ orbits in the inner Solar System, the TRAPPIST-1 system, and Jupiter’s Galilean moons. Credit: IoA/Amanda Smith.

All seven planets are close to their star.
They orbit real fast since they’re not very far
Planet b’s year: one and a half Earth days.
If you lived there you’d have all sorts of birthdays!

Stand on a planet in the TRAPPIST-1 system
Oh, the planets you’d see in the sky – you can’t miss ‘em!
Their orbits are so close that they’d each appear
As big as the full Moon! Bigger when they’re near.
(Imagine the werewolf problem they must fear!)

The Sun in the sky would stay in the same place.
The planets always show to their star the same face.
The planets would shift and sometimes look like crescents
A peek at that sky’s like an antidepressant!

The two inner planets, planets b and c,
are too hot for oceans. They’d be real steamy.
But the four planets after: d, e, f, and g
are all at about the right place for a sea.
They could have liquid water, although
We don’t know if they even have H2 or O.
There’s plenty of planets out there that are dry
Just look at that big red dot up in Earth’s sky.
That’s Mars, it’s got water but only a trace;
And Venus, of course, is a hot hot dry place.

Comparison of the energy received by the TRAPPIST-1 planets from their star with that received by our terrestrial planets from the Sun. TRAPPIST-1 planets d, e, and f (and possibly c and g) are good candidates for liquid water. Credit: IoA/Amanda Smith.

The planets’ orbits were not set by chance
They seem to be following a cool cosmic dance
Take for example planets d and e
When e completes two orbits, d has done three.
They meet up again at the very same place
This orbital resonance is common in space.
Each pair of planets is in resonance. So,
It’s like the whole system is doing a tango!

We think that a resonant configuration
Is a signpost of the planets’ migration
That means that the planets’ orbits shifted
While they were forming, inward they drifted.

One cool last thing I really should say-o
TRAPPIST-1’s connected to Galileo!
He found four big moons orbiting Jupiter’s skies
And the TRAPPIST-1 star is about Jupiter’s size

Comparison of the orbital periods of the TRAPPIST-1 planets with Jupiter’s Galilean moons. The relative sizes of objects are correct, but the orbital distances of the TRAPPIST-1 system are much larger. Credit: IoA/Amanda Smith.

Now let’s wrap up with a ditty for later
It’s written for you if you’re a planet hater

“Planets”, you say, “no big deal. There’s a zillion.
Eight in our Solar System and a billion
In orbit around other stars in the sky
Why should I care about this one little guy?”

I’d answer your question with a look back at history
Discovering new planets may help solve a big mystery.
Are we all alone? Is there other smart life?
(Do I have an alien doppelganger and wife?)

How can we answer this key age-old question?
It’s not at all simple. But here’s a suggestion
Any life out there will need its own planet
Maybe with oceans or ice caps or granite.
We now have the telescopes, tools and techniques
To find other planets and take a sneak peak
To try to find out if the Earth is unique.

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