More Details from Hubble Reveal Strange Exoplanet is a Steamy Waterworld


Would Kevin Costner’s character in the movie “Waterworld” be at home on this exoplanet? The planet GJ 1214b was discovered in 2009 and was one of the first planets where an atmosphere was detected. In 2010, scientists were able to measure the atmosphere, finding it likely was composed mainly of water. Now, with infrared spectra taken during transit observations by the Hubble Space Telescope, scientists say this world is even more unique, and that it represents a new class of planet: a waterworld underneath a thick, steamy atmosphere.

“GJ 1214b is like no planet we know of,” said Zachary Berta of the Harvard-Smithsonian Center for Astrophysics (CfA). “A huge fraction of its mass is made up of water.”

GJ 1214b is a super-Earth — smaller than Uranus but larger than Earth — and is about 2.7 times Earth’s diameter. That gives it a volume 20 times as great as Earth yet it has less than seven times as much mass, so it’s actually kind of a lightweight. This world is also hot: it orbits a red-dwarf star every 38 hours at a distance of 2 million kilometers, giving it an estimated temperature of 230 degrees Celsius.

Berta and a team of international astronomers used Hubble’s Wide Field Camera 3 (WFC3) to study GJ 1214b when it crossed in front of its host star. During such a transit, the star’s light is filtered through the planet’s atmosphere, giving clues to the mix of gases.

“We’re using Hubble to measure the infrared color of sunset on this world,” Berta said.

Hazes are more transparent to infrared light than to visible light, so the Hubble observations help to tell the difference between a steamy and a hazy atmosphere. They found the spectrum of GJ 1214b to be featureless over a wide range of wavelengths, or colors. The atmospheric model most consistent with the Hubble data is a dense atmosphere of water vapor.

Since the planet’s mass and size are known, astronomers can calculate the density, of only about 2 grams per cubic centimetre. Water has a density of 1 gram per cubic centimetre, while Earth’s average density is 5.5 grams per cubic centimetre. This suggests that GJ 1214b has much more water than Earth does, and much less rock.

As a result, the internal structure of GJ 1214b would be extraordinarily different from that of our world.

“The high temperatures and high pressures would form exotic materials like ‘hot ice’ or ‘superfluid water’, substances that are completely alien to our everyday experience,” Berta said.

Theorists expect that GJ 1214b formed further out from its star, where water ice was plentiful; later the planet migrated inward towards the star. In the process, it would have passed through the star’s habitable zone, where surface temperatures would be similar to Earth’s. How long it lingered there is unknown.

GJ 1214b is located in the constellation of Ophiuchus (The Serpent Bearer), and just 40 light-years from Earth. Scientists say it will be a prime candidate for study by the NASA/ESA/CSA James Webb Space Telescope, planned for launch later this decade.

This article was updated on Feb. 23

Read the team’s paper (pdf).

Source: ESA Hubble

24 Replies to “More Details from Hubble Reveal Strange Exoplanet is a Steamy Waterworld”

  1. I don’t think a science fiction writer ever thought up an evolution happening on such a world
    Polarized light for vision, maybe a densily packed stratosphere for some cooling below and who knows: biological “steamengines” as powersource.

    1. I can remember 3 straight up.

      One was on an oxygen rich world with nightmarish energetic predators. One was on water worlds as habitats for a galactic exodus and what adaptations went into that.

      The more interesting one was on floating biochemical polymer mats. It tied in with the novel’s theme of a computer immersed world, where some sentients choose to live entirely as simulacrums. The mats were at the basis “soup” mats self-replicating by breaking, but at a higher level coding for computational worlds with sentient codes by way of its chemical combinatorial growth making a Turing mechanism.

      Hence the mats were both life and sentient computing, which satisfied neither of the two polarities of the Earth civilization, outgoing vs withdrawn, yet by its novelty shored up the use of actual interaction with the outside world.

      1. to DeRon and Torbjörn,

        I stand corrected 🙂

        Btw Torbjörn, your more extensive story sounds like a small side line from one of Alastair Reynolds’ books?

      2. It’s the famous dare, to imagine something not already written about. =D

        I was able to check on your question, since I have the novel collection in my shelves right now. It’s from “Extreme Science Fiction” (a gift, but in my tastes), and “Wang’s carpets” are Greg Egan.

        It also has the oxygen world “Waterworld”, by Gillet & Oltion.

        Since Reynold’s has recently irritated my sense of propriety on science fiction, I can take the opportunity to rant:

        I’m actually reading Reynold’s books, but his unwarranted accommodationism towards religion has made me throw out some of them. It’s just too annoying to have unembarrassed religion thrown at you everywhere you go. If I liked it I would search it out, thank you very much.

        It is also annoying to have to put up with such a foolish premise and Reynold’s bungled attempts to merge nature and superstition. It’s like the Stargate fiasco all over again. (You know, “we aren’t _primitively_ religious, just sophistheologically believing in invisible skydaddys that aren’t out to fool people as weak impostors anyone can reveal, the American way”. Right.)

        I’m just wrapping up a series of Reynold’s, then I will let him slip into the ocean again for more sane fishes.

        Same goes for Egan of course, who is religious and let it show at times. But that short story was just skirting the issues of his searched for dualism. And generally I can’t throw away a collection of short stories just because some are too stupid to be read.

        Whew! I just feel so much better now. ???o???

  2. Hot ice eh? Since solid water is less dense than liquid water and there would be much gravity, heat and pressure under a dense atmosphere on a planet orbiting at 1/50th our earth/sun distance, then with the heat, wouldn’t ice be pretty excited to turn to water??

    1. That only applies to water on more normal pressures, and is caused by the very specific crystal phase that ice takes on. At a pressure of 10GPa ice is still solid at 600K (327 C) and higher pressures move the melting point upwards.

      Water under extreme pressures have a radically different crystal phase, as well as a different liquid phase. similar to how the hydrogen near the core of jupiter is liquid or even solid at 30000K. The different phases sort of loses significance under these conditions, for one because solids behave more like plastics or clay.

      Other than that, i also see lots of opportunity for convection being an important mechanism here.

      1. Water ice was my first special project in school, and I remember there is a _lot_ of phases. [What can I say, I grew up in icy Sweden, and snow & ice are fun toys.]

        One reason is the peculiar hydrogen bond. One other is the relatively large impact of hydrogen isotopes, as water is a light molecule with relatively much hydrogen.

      2. I hate it when I get late to work because I have to zig-zag between all the polarbears on the streets … 😛

      3. Ha, I was writing “icy” Sweden, before I settled for something that wouldn’t conjure up them bears.

        Unfortunately they are pesky critters. “?|?|?

      4. “Phases of matter” is another one of those scientific concepts that on the face of it ought to be really simple (3 types, no grey areas) and yet in reality is a horrifying mess. Such is the universe!

  3. I calculated from the mass and radius quoted the density would be 1.9g/cc, which suggests that this planet is not quite a terrestrial planet, nor is it quite a gas giant. I suspect the H_2O is considerable, maybe composing up to a half of the planet’s mass. This may be some intermediate from between gas giant and terrestrial.

    At extreme pressures and temperatures water enter different phases. A superheated form of H_2O vapor is of considerable interest to those who design steam turbines. Water at above 1000C enters into a superheated phase. Similarly at extreme pressures and lower temperatures there exists a superheated solid phase. This H_2O atmosphere may extend a thousand or more kilometers in depth, where you can be sure the interior, or where the H_2O makes contact with rock, is utterly horrendous by our standards for planetary environments.

    Of course this is nothing compared to the pressures inside a neutron star which reach 10^{34}Pa.


    1. I agree that there would have to be significant amounts of water on this planet, but wouldnt Uranus or Neptune be suspected to show a similar display if they where in that same position?

      They must have significant amounts of water inside, only because of the lower temperatures it is frosen out of the atmosphere and very little is shown spectroscopically. Water, ammonia, methane etc probably forms some kind of slush deeper inside which also dissolves gaseous compounds like hydrogen and helium (yes, helium solves very well in water under high pressures).

      At the higher temperatures, water would show up abundantly also in the upper atmosphere.

      But then, where are the signs of other expected gases? Methane, ammonia, carbon-monoxide and -dioxide etc…

      1. The extreme temperature and pressure had a strong influence in the chemical equilibrium reached for the following reactions:

        2NH3 = N2 + 3H2 [R1]
        2NH3 + CO = N2 + CH4 +H2O [R2]
        2NH3 +3CO2 = N2 + 3CO + 3H2O [R3]

        CH4 +H2O = CO +3H2 [R4]
        CH4 +2H2O = CO2 +4H2 [R5]
        CH4 + CO2 = 2CO +2H2 [R6]
        CO2 + H2 = CO + H2O [R7]

        For all of them, increasing temperature shifts the equilibrium to the right side of the chemical equations above.

        The first 3 reactions determine the stability of ammonia. The strongest constraint comes from reaction R1 (the reverse Haber Process): at temperatures of more than 200ºC and low pressures(around 1 atmosphere), ammonia decomposes into nitrogen and hydrogen.

        The next 3 reactions determine the stability of methane.Those are the reactions used in Syngas (Synthetic Gas) reactors (see here: ). Beyond 800ºC, there is total (100%) methane destruction by reactions R4 to R6.

        Carbon dioxide reduction to carbon monoxide is also important at several hundred ºC, and increases with temperature like all the other 7 reactions.

        For planetary atmospheres that can be studied spectroscopically, only the low pressure (near 1 atm) layers are relevant. The temperature of course depend on the distance from the star and the greenhouse effect.

        For this hot planet, expect very little or no ammonia.There may be some methane, but I think carbon will likely be mostly in the form of CO and CO2. And of course we have water vapor.

        Uranus and Neptune, being so far from the Sun are very cold, resulting in little or no CO2 and CO, because at low temperatures the reactions tend to the left side of the above equation (CH4 and H2O). H2O and NH3 are frozen forming water/ammonia ice clouds, while methane form some % of the atmosphere.

    2. “This may be some intermediate from between gas giant and terrestrial.”

      In effect, this planet seems to be like an ice giant, like Uranus and Neptune. However, this is a smaller planet: 2,7 times the Earth radius (Neptune is 3.9 times the Earth radius, Uranus is 4) and a mass times Earth mass (Neptune is 17 times Earth mass, Uranus is 14.5).

      When the planet was discovered, it was inmediately called a “Super Earth”. To my disappointment, however, it has a density of 1.9 g/cc, similar to the values for Uranus(1.3) and Neptune(1.6). This make it a “mini-Neptune”, not a “Super Earth”!

      There was still one possibility: the atmosphere of this planet is not like the one of Uranus and Neptune, but a steam atmosphere made mostly of water vapor, along with other gases like CH4, CO, CO2, N2,etc.

      If this is the case, then an identical planet orbiting his star in a more distant orbit (resulting in a cooler atmosphere) would have most of these compounds condensed to either liquid water or solid ice, so it will have a much thinner atmosphere resulting in a smaller radius and a greater density (a density similar to the moons around the planets in the outer solar system). In the case of such a planet inside the HZ, it would be a potentially habitable “ocean planet”, having a liquid water ocean hundreds of meters deep, that rests above a “warm ice” mantle thousands of meters thick. For more distant (cooler) ocean planets outside the HZ, they would be giant iceballs.

      The results of spectrum of the atmosphere now rule out the H2/He dominated atmosphere, but the spectrum is not exactly like the 100% water vapor case. The paper suspects a mix of H2 and H2O. If this is the case, this planet is after all still a mini-Neptune, only smaller and a bit more dense.

      Could it still be a H2O/CO/CH4/CO2 mix, or the possibility of this being a failed “ocean planet” is refuted by the data?

      1. The H_2 is as you indicate below probably due to the reactions you point out below.

        This planet may be a Geoneptune or Neptugeo planet. It seems to be physically in some intermediate zone between being a terrestrial planet and a small Neptunian gas sub-giant. It has some density characteristics similar to Neptune, but maybe just enough larger so it is has more than 50% rocky material.

        I am beginning to think anyone can come up with a description of a planet with almost any chemical composition, orbital radius, rotation, and temperature, run the model and there will probably be a planet out there at least similar to that.


      2. The H_2 is as you indicate below probably due to the reactions you point out below.

        This planet may be a Geoneptune or Neptugeo planet. It seems to be physically in some intermediate zone between being a terrestrial planet and a small Neptunian gas sub-giant. It has some density characteristics similar to Neptune, but maybe just enough larger so it is has more than 50% rocky material.

        I am beginning to think anyone can come up with a description of a planet with almost any chemical composition, orbital radius, rotation, and temperature, run the model and there will probably be a planet out there at least similar to that.


    3. Of course, the H2O is probably not in contact with *solid* rock. Probably a viscous mantle, maybe with mountains whipped up from storm vortices above.

  4. Not true. Several science fiction writers have postulated on deep sea life evolving intelligence. In one instance, these tube like animals, called Eulers, were thought to be math based intelligence who thought in equations. In another, the mollusk like life forms communicated via radio waves. Both of these species are in the series, “Inheritence Trilogy” by Ian Douglas.

  5. My calculation:
    I calculated the distance of this planet in between the distance of 4.099517^19 cm to 3.347×10^19 cm. It means that the planet may not be rotate in circular path around the star.
    Calculation: Avo. No. / R ?^2 x (?3/2) = 4.099517^19 cm , j = 3/2 = angular quantum number.
    And Avo. No. / R ?^2 = 3.347×10^19 cm. , R = ratio of atom and electron.
    Nirmalendu Das

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