What’s so special about Trappist 1

An otherwise unremarkable small, cool and rather faint (19 magnitude, less than Pluto, just to be clear) dwarf star located 39.5 light-years from the Sun in the constellation Aquarius, Trappist 1 has become in the last two weeks or so a real celebrity – being the only system, so far, found out there to be similar to ours, and not just because it contains seven planets of dimensions and characteristics similar to our Earth. Trappist 1 is more special than that, and deserves the hype astronomers around the world have credited to its discovery.

Here the abstract from the article published in Nature on 23 February 2017. “Recently, three Earth-sized planets were detected that transit (that is, pass in front of) a star with a mass just eight per cent that of the Sun, located 12 parsecs away. The transiting configuration of these planets, combined with the Jupiter-like size of their host star—named TRAPPIST-1—makes possible in-depth studies of their atmospheric properties with present-day and future astronomical facilities. Here we report the results of a photometric monitoring campaign of that star from the ground and space. Our observations reveal that at least seven planets with sizes and masses similar to those of Earth revolve around TRAPPIST-1. The six inner planets form a near-resonant chain, such that their orbital periods (1.51, 2.42, 4.04, 6.06, 9.1 and 12.35 days) are near-ratios of small integers. This architecture suggests that the planets formed farther from the star and migrated inwards. Moreover, the seven planets have equilibrium temperatures low enough to make possible the presence of liquid water on their surfaces.” (You can read the whole article online at this link).

Intriguing, isn’t it? Its bizarre name comes from The Transiting Planets and Planetesimals Small Telescope (TRAPPIST) located in Chile. Already in May 2016, researchers using TRAPPIST system announced the discovery of three planets in the same system. Later on,  Spitzer confirmed the existence of two of these planets and discovered five additional ones, increasing the number of known planets in the system to seven.

The star itself is rather small, with 8% the mass of and 11% the radius of the Sun is only a bit larger than Jupiter, albeit 84 times more massive. It has a temperature of 2550 K, and this means it has not completely cooked out the surface of orbiting planets, no matter how close they are. And, another interesting detail, is at least 500 million years old and with the odds of living up to 12 trillion years more. More than enough for life to evolve.

For more about this fascinating system, I suggest having a look at the NASA page on the discovery, which I quote here:

The seven wonders of TRAPPIST-1 are the first Earth-size planets that have been found orbiting this kind of star,” said Michael Gillon, lead author of the paper and the principal investigator of the TRAPPIST exoplanet survey at the University of Liege, Belgium. “It is also the best target yet for studying the atmospheres of potentially habitable, Earth-size worlds.”

For a good picture gallery and artist impressions on the planet, I recommend the series prepared by Space.com at this link.

In alternative, if you want the whole story in a quite accurate, and entertaining, graphic story, have a look at this one.

Finally. this is a cool video about the discovery and the seven planets. Happy watching!


  1. sjhigbee

    Wow… thank you once more for your excellent article. This is HUGE… Have a great week, Steph:)

    1. Steph P. Bianchini (Post author)

      Thanks Sara – can’t wait to hear more about this intriguing system!

  2. ccyager

    Thanks for posting this! What a discovery. And so much closer than other systems that have made news in the past. I wonder if it’s close enough that if it does have intelligent sentient life, it could visit us or we them?

    1. Steph P. Bianchini (Post author)

      Yes, this is really interesting. We won’t be able to visit with our current technology and I doubt, given the system’s age, there’s any intelligent life over there – yet. But it will live long, so it might happen at some time in the future.

  3. maddalena@spaceandsorcery

    Since this discovery was announced I’ve been awash with enthusiasm: true, it’s still early stages and it’s more a matter of informed hypotheses than real, hard data, but for people like us who love to dream about life on other planets, this has the definite feel of the real thing – the real possibility of either another form of life or an alternate place where humanity could thrive. Amazing 🙂
    Thanks for sharing!

    1. Steph P. Bianchini (Post author)

      Yes – I bet we’re going to see/read SF stories about Trappist I anytime soon 😀


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