TRAPPIST-1 | Vol. 4 / No. 17.4

Image: NASA/JPL-Caltech/R. Hurt, T. Pyle (IPAC)

Things are so exciting in the field of exoplanet discovery these days, and yesterday they just got even more so.

In a press conference yesterday afternoon, NASA announced the discovery of a seriously cool planetary system. TRAPPIST-1 is 39 light-years away, and has seven Earth-sized planets in it. And three of them are in the so-called “goldilocks” zone. Technically we already knew about the system. It was announced in May that the TRAPPIST telescope (Transiting Planets and Planetesimals Small Telescope) in Chile had found three planets in the system, and this latest announcement concerns refined observations by the NASA Spitzer Space Telescope and ground-based telescopes like the European Southern Observatory’s Very Large Telescope (VLT).

So what do we know about this system? Well, for starters, it’s seriously small. TRAPPIST-1 — named for — is an ultra-cool red dwarf, and it’s pretty small. It’s 0.114 solar radii. Just for the record, Jupiter’s roughly 0.1 solar radii, so that’s what we’re talking about here. Now it’s got about eighty times the mass of Jupiter (0.08 (+/- 0.009) solar masses, vs roughly 0.001 solar masses), which is why it’s a star and not a big old radioactive planet, but even so, the scale we’re dealing with isn’t very large. The entire TRAPPIST-1 system would fit within a fraction of the orbit of Mercury.

And yet there are seven Earth-sized planets there.

Photo: Caltech/IPAC/JPL/NASA.

As you can see in this comparison, the green areas are the “habitable zone.” Now you’ll notice above that Venus and Mars are both technically in our system’s “habitable” zone, so there’s no actual indication of habitability. What it means is that, under the right circumstances — maybe with the right atmosphere, the right magnetic field, the right rotational period — it’s possible for liquid water to pool on the surface of the planet. Under the wrong circumstances, well, you’ve seen Venus and Mars, right?

And as is the case with tiny star systems, these things are just flinging around their star. TRAPPIST-1b (the closest one, a is the star itself) goes around its star every 1.51 days. The potentially habitable ones (e, f, and g) fling around at 6.1, 9.21, and 12.35 days each, respectively. That’s at best a two week year. And when planets are that close to their stars, they often become tidally locked — right now we know the closest two, b and c, definitely are. There’s still some debate in the scientific community about it, but tidally-locked planets aren’t considered great places to live, mostly because one side is so hot you die, and the other side is so cold you die.

Image: NASA/JPL-Caltech/R. Hurt, T. Pyle (IPAC)

We don’t know if they have atmospheres, or if they do, what they’re made of. But the simple existence of systems like this — and in our “neighbourhood” — really ups the chances that we’ll someday find life out there.

The next step will be after we launch the James Webb Space Telescope next year. It should have the sensitivity to detect whether they have atmospheres and if so whether they have the markers of life in them. Meanwhile TRAPPIST and Spitzer and many others will be searching for more systems like this going forward. Because maybe this is just the tip of the iceberg.

I can’t wait.

You can learn more about TRAPPIST-1 over at NASA.


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Richard Ford Burley is a human, writer, and doctoral candidate at Boston College, as well as Deputy Managing Editor at Ledger, the first academic journal devoted to Bitcoin and other cryptocurrencies. In his spare time he writes about science, skepticism, feminism, and futurism here at This Week In Tomorrow.