Water worlds? Updated masses for TRAPPIST-1 planets

Artist’s conception of some of the planets in the TRAPPIST-1 planetary system. Image Credit: ESO/M. Kornmesser/N. Risinger (skysurvey.org)

There is an interesting new paper out about the seven near-Earth-sized exoplanets orbiting the star TRAPPIST-1. According to the study, four of the planets may be true water worlds, although just what form those may take isn’t clear. All seven planets are close in size to the Earth, with some of them in the star’s habitable zone, where temperatures could allow liquid water on rocky surfaces.

From the paper:

“The newly detected TRAPPIST-1 system, with seven low-mass, roughly Earth-sized planets transiting a nearby ultra-cool dwarf, is one of the most important exoplanet discoveries to date… Figure 4 indicates that – to within the errors of our determinations – the four most distant planets are consistent with pure water compositions, and in any event, are substantially less dense either Mars or Venus… The planets orbiting TRAPPIST-1 arguably constitute the most important exoplanetary system yet discovered. The planets’ large observed transit depths, coupled with the occurrence of extensive transit timing variations, present an extraordinary opportunity to discern the masses, the densities, the compositions, and the dynamical architecture of low-mass worlds. As more data are collected, substantial insights will be gained by an evolving comparison of these newly detected planets to the familiar terrestrial worlds of our own Solar System.

It will be interesting to see what further studies reveal. More information on the TRAPPIST-1 planets, including observations by Kepler, is here and here.

6 thoughts on “Water worlds? Updated masses for TRAPPIST-1 planets

  1. Any sentient life on one of those planets (2? 3? …) would have an enormous incentive to develop space-faring technology to get to and inhabit the other worlds in their system. They might not even need special breathing equipment on a similarly sized water world. And this is before knowing about the possibility of life-bearing moons too. Gee, with somewhat better telescopes, maybe we can detect objects traveling between worlds with non-elliptical paths, i.e. spaceships….

    • Unfortunately a complete water world with such low densities as these Trappist-1 planets (which likely has an oceanic depth many times that of Earth’s) would preclude any chance of a technological civilization developing, let alone a spacefaring one. Any sentient creature would be forever trapped in their ocean, unable to escape regardless of intellectual prowess.

      The reason for this is two-fold of differing weights. First, the species would need tool making capable bodies, and second, they would need tools… which are non-existent on a water world in their most simplest form even when considering maximum seafloor exploitation (assuming the ocean is shallow based to begin with).

      I write about this limitation more extensively in my book, http://www.ourcosmicstory.com.

      • I wasn’t able to get your link to work. But anyway, I’m not sure being water-bound precludes tool-making or resource acquiring abilities. Octopuses seem pretty smart and agile with 8 arms, and have even been the basis of hypothesized sentient creatures in some sci fi (not just on The Simpsons). And there are lots of minerals and fossil fuels in the sea too.

        • Apologies about that, something is wrong with using www. Please try it without the prefix:


          It does preclude it for several reasons, unfortunately. Octopuses are smart, sure, and they are indeed the right step on the way to tool making bodies. However, they are still bound by their watery surroundings. Entire water worlds don’t preclude the ability for life to evolve tool making appendages so much as make it difficult for evolution to find an advantage in producing them in the first place.

          Let’s keep to squid though for the next issue, since they have appendages that could work well enough. What is the real nail in the coffin is actual tool making. While there may be minerals in the sea, they are diluted and unusable except for conservative biological processes. There’s no way else to get to them. Even with biological processes, there’s no known connection between using minerals diffusely and somehow getting the ability to mass gather them to built technology. Then there is the problem of lack of fire, which is an important catalyst in being able to put those materials to work.

          How do you forge metals to build a rock ship when you first need the ore crafted in multiple steps, not to mention specialized plastics and hundreds of other materials, when all you have to work with initially is seawater, and the ocean floor is kilometers too far below for you to get too for your biological body, not to mention again the issue of putting to work the materials you do find? You see the problem.

          Think of it like a ladder with 10 rungs missing… sure, you ‘could’ get to the top if you could just reach that next set of rungs, but there’s a gap too large to cross with what you’ve got. You’re stuck, even if everything is visually laid out before you. I’m not saying it’s impossible per se, as there’s a chance that everything will come together still in some unforeseen unique way, but for the purposes of practical considerations on what is basic knowledge of physics, chemistry, etc., it’ll certainly not be the expected norm.

          There are many many good reasons to think technological civilizations will be found on worlds with at least some percentage of land. Estimates have suggested that on super-Earths, even just 10% land coverage would be plenty for water born species to gather enough resources from the coastal areas, not to mention species that eventually migrate entirely onto land.

          So it’s not a negative that water worlds won’t be technologically habitable for the vast majority (or all of them), we have plenty of other worlds to consider yet.

  2. Planet h is now UNQUESTIONABLY the most bizarre planet discovered to date. with a most likely mass of LESS THAN ONE TENTH THAT OF EARTH, and a radius exactly halfway between Mars and Earth, It CANNOT be the spherical “iceball” with little to no atmosphere as it is usually potrayed in artistd renditions. Neither can it be a MINI “mini-neptune” with a predominantly Hydrogen atmosphere. With a surface gravity THAT LOW combined with the ABSOLUTELY BRUTAL FLARING going on(extreme NOW according to Kepler data, and PROBABLY MUCH WORSE 3 billion years ago in its infancy, ALL OF ITS HYDROGEN MUST HAVE ESCAPES LONG AGO! What remains is something out of science fiction(LITERALLY: Robert Forward’s “Rocheworld”)! Due to its ridiculously LOW surface gravity(less than the MOON’s), TRAPPIST-1’s gravity pulls the starward hemosphere of TRAPPIST-1h TOWARD IT, forming a Fabrege egg-shaped “Eau Lobe”. Despite its 167K frigid temperature, the majority of its atmosphere would MIGRATE to the stellar point, providing an “insulating blanket” sufficient to keep the stellar point water in a permanently liquid form. The atmospheric surface pressure would be something akin to the surface pressure at the bottom of Challenger Deep in the Pacific Ocean. However, the surface pressure would be more akin to that of Venus at the terminator, and similarto our own at the anti-stellar point. If the atmosphere consists primarily of Oxygen, Carbon Dioxide, and Water vapor, there could even be an ice sheet at the anti-stellar point! SCIENCE FICTION WRITERS: GO NUTS!!!

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