TRAPPIST-1 Exoplanets Might All Be Water Worlds

By Nathaniel Scharping | February 5, 2018 3:47 pm
An artist's impression of the TRAPPIST-1 system. (Credit: ESO/M. Kornmesser)

An artist’s impression of the TRAPPIST-1 system. (Credit: ESO/M. Kornmesser)

A series of papers out today gives us further insights into the TRAPPIST-1 system discovered in 2016.

The seven planets that make up the system orbit a dim red dwarf star much smaller and cooler than our own Sun. The planets’ orbits are much tighter than in our solar system, and they’re all closer to their home star than Mercury is to the Sun. Three of them are thought to be in the “habitable zone” where liquid water could exist.


The system is relatively close, only 40 light-years away, and astronomers have been probing the planets and their star with an array of telescopes to learn about how TRAPPIST-1 formed and what conditions might be like on the seven planets. The latest research provides a much better estimation of some of the planets’ densities and helps narrow down the possibilities for atmospheres there. Most excitingly, astronomers now say that water appears to be present in significant quantities on all of the planets, in some cases up to five percent of the planet’s mass.

Because conventional telescopes aren’t powerful enough to get useful information about the planets directly, astronomers have to rely on other methods. To get a better idea of their density, and thus what they might be made of, the researchers tracked each planet’s orbit. The TRAPPIST-1 planets are so close together that their gravitational fields tug on each other as they spin around their star. By measuring the power of these tugs, and putting that data into a sophisticated computer modeling algorithm, the researchers were able to get an idea of how dense each planet was.

The picture it paints is rough, but the researchers found that the planets weren’t dense enough to be made of just rock and metal. Volatiles—elements and compounds with low boiling temperatures—must be present, they say, and the best explanation is water. The amount varies, but some planets could potentially have more water than exists on Earth. Water could be liquid on the three planets within the habitable zone, the researchers say in a paper published in the journal Astronomy & Astrophysics. On planets further from the star, a layer of ice may cover the surface, and on the second planet from the star, a thick atmosphere of water vapor is likely present.

“Densities, while important clues to the planets’ compositions, do not say anything about habitability. However, our study is an important step forward as we continue to explore whether these planets could support life,” said Brice-Olivier Demory a study co-author from the University of Bern in a news release.

In the Air

Atmospheres could exist on several of the other planets closer in as well, and another paper, also published on Monday in Nature Astronomy, details researchers’ efforts to peer into those gaseous layers with the Hubble telescope.

When a planet passes in front of a star, some of the light will shine through its atmosphere, if it has one. If any gases are present, they will alter the light in a predictable way, allowing astronomers to see what molecules are floating around in the atmosphere. In this case, the researchers were looking to see whether the three planets in the habitable zone, as well as one other, had the kind of thick atmospheres that typify gas giants in our own solar system. Such an atmosphere would be rich in hydrogen and cloud-free, and would make discovering liquid water on the surface less likely.

After analyzing the data from Hubble, the researchers found no traces of such atmospheres though, meaning that the planets are likely terrestrial like Earth or Mars. An atmosphere of some sort could still exist there, of course, but it’s likely not as puffy and smothering as the kind that blankets planets like Neptune.

These observations pushed Hubble capabilities to the edge, the researchers say. For better data, we’ll have to wait for the telescope’s successor, the James Webb Space Telescope, set to be launched in 2019. It should allow for the detection of heavier gases in the atmosphere and help to refine our search for life.

CATEGORIZED UNDER: Space & Physics, top posts
MORE ABOUT: exoplanet
  • Uncle Al

    Send the Trappists a repetitive radio message for years on end re Contact (1997), that ends with”…Earthlings are delicious and abundant.” Some date around 2100 say “Howdy!, are you here to serve mankind?”

    • OWilson

      Took me longer to say much the same thing.

      Credit due, thanks!

      • Uncle Al

        … Jes’ doin’ what comes uinnaturally.

        • OWilson

          We got to the top of the food chain by devouring and slaughtering everything below us.

          They want us to spend a lot of money to search for our intellectual ‘superiors’ ? :)

  • Mike Richardson

    When I was a kid, exoplanets were just a matter of speculation, and it was assumed we’d need a very large telescope on the moon or a spread out interferometer array in space to find them, much less determine whether they had atmospheres. It amazes me how much information astronomers have been able to glean through more indirect methods, such as the density calculations described here. It really makes me excited to think what discoveries await the next generation of space telescopes and mega scopes here in earth!

    • okiejoe

      And think how many planetary systems we are missing because their poles are pointing our way and we never see a planetary transit.

      • Mike Richardson

        That’s true. We’re just getting a sample of what’s out there, due to the inherent limitations of this method. Fortunately, within the next decade, direct imaging techniques from a new generation of telescopes in space and larger ground-based scopes should start finding the non-transitting worlds.

        • Moe

          Hello Mike. kindly advice who led this team of astronomers and was he from NASA or ESA?

          • Mike Richardson

            Michael Gillon of the University of Liege, Belgium. The team is an international collaboration involving NASA and the European Southern Observatory, as well as various universities. For more information, search for the TRAPPIST-1 survey team’s home page — I tried including a link, but apparently that’s not allowed.

          • Moe

            Thank you Mike.

  • OWilson

    Interesting speculation, but still speculation nonetheless. unsatisfying in the same way that life on Mars, and the “probable” finding of the God Particle was.

    Voyager 2 is about the limit of current technology, and at that rate it would still take some 3,000,000 years to travel to this “relatively close” solar system, to find out!

    From this distance we can only guess if it is dead, like everything else we can see. At 4.5 light years, best bang for the buck would be to saturate these exoplanets with simple electronic signals, the wait for 10 years or so for an answer.

    Of course we would have to get all the major countries to sign some kind of waiver “Accord” to agree to potentially becoming dinner for a cosmic Kim Il Un. :) That may delay things, a bit!

    Maybe the answers are to be found here on Earth.

    Like, they tell us life is abundant in the Universe, and will start up anywhere, given the proper recipe!

    So lab life creation should’t be problem, and we’ll have that little problem solved, right?

    Maybe then we can figure out some of the important questions like, what is the Universe really made of?

  • Brian McInnis

    The word you’re looking for is ‘planets’.
    If they’re non-Solar planets, you’re free to specify.


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