Our Milky Way galaxy may be teeming with ocean worlds

This visualization depicts NASA's Cassini spacecraft flying through plumes on Enceladus in October 2015. (Image credit: NASA/JPL-Caltech)

Far-off alien planets covered in vast oceans might be common in our Milky Way galaxy, scientists find. 

"Ocean worlds" are terrestrial planets that have significant amounts of water either on their surfaces or in a subsurface sea. Right here in our own solar system, Saturn and Jupiter host moons that fall under this watery category. For example, Enceladus, Saturn's geyser-spewing moon, has a massive, global ocean made up of liquid saltwater that lies just below its icy surface. But how common are these "ocean worlds" throughout the cosmos? 

In a new study, researchers decided to see how many planets in the Milky Way might fit into the category of "ocean world." They also wanted to explore how many of these worlds might even spit watery plumes, stemming from their oceans, out into space as Enceladus does. And they found that more than a quarter of the 53 exoplanets they studied could potentially be ocean worlds.

Related: 6 Most Likely Places for Alien Life in the Solar System

"Plumes of water erupt from Europa and Enceladus, so we can tell that these bodies have subsurface oceans beneath their ice shells, and they have energy that drives the plumes, which are two requirements for life as we know it," Lynnae Quick, a planetary scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, who specializes in volcanism and ocean worlds, said in a NASA statement. (Europa is one of Jupiter's many moons.)

"So if we're thinking about these places as being possibly habitable, maybe bigger versions of them in other planetary systems are habitable too," Quick said.

To figure out how many of these ocean worlds might be lurking out there in the Milky Way, the scientists looked at 53 exoplanets that are a similar size to Earth, including the seven planets of the nearby TRAPPIST-1 system. They analyzed variables including exoplanet size, density, orbit, surface temperature, mass and distance from their star.  

In addition to estimating that about a quarter of these planets could be ocean worlds, the team also found that most of them could have subsurface oceans under layers of ice. Additionally, the team found that many of these possible ocean worlds could be releasing even more energy than Enceladus and Europa do. 

Now, "assumptions that go into these mathematical models are educated guesses," the NASA statement reads. However, this information could be important in helping researchers to better choose which exoplanets they might want to study or where they might send probes in the future. 

In the future, scientists could also test Quick's findings by measuring the heat emitted by these worlds or by identifying any volcanic (or cryovolcanic, which includes liquid or vapor emissions instead of molten rock) eruptions. These could be identified in the light (and the wavelengths of that light) filtered out by a planet's atmosphere. 

These exoplanets are too far away to currently see in detail, especially because such details are often obscured by the light of a planet's star. However, with future missions including NASA's James Webb Space Telescope, which is set to launch sometime in  2021, researchers could more closely investigate these worlds. 

"Future missions to look for signs of life beyond the solar system are focused on planets like ours that have a global biosphere that's so abundant it's changing the chemistry of the whole atmosphere," Aki Roberge, a NASA Goddard astrophysicist who collaborated with Quick on this analysis, added in the same statement. "But in the solar system, icy moons with oceans, which are far from the heat of the sun, still have shown that they have the features we think are required for life."

Email Chelsea Gohd at cgohd@space.com or follow her on Twitter @chelsea_gohd. Follow us on Twitter @Spacedotcom and on Facebook.

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Chelsea Gohd
Senior Writer

Chelsea “Foxanne” Gohd joined Space.com in 2018 and is now a Senior Writer, writing about everything from climate change to planetary science and human spaceflight in both articles and on-camera in videos. With a degree in Public Health and biological sciences, Chelsea has written and worked for institutions including the American Museum of Natural History, Scientific American, Discover Magazine Blog, Astronomy Magazine and Live Science. When not writing, editing or filming something space-y, Chelsea "Foxanne" Gohd is writing music and performing as Foxanne, even launching a song to space in 2021 with Inspiration4. You can follow her on Twitter @chelsea_gohd and @foxannemusic.

  • Ted A Campbell
    Seems to me that there are too many articles here with "may be" alien life. There may be alien life. Is that news? I suppose it must sell. I'd prefer to see about 90% "is" stories rather than "may be" stories.
  • Wolfshadw
    While I agree with you, I think the problem is that science is mostly theory and few facts. If editorial waited for just confirmed facts before publishing anything, we'd have maybe one or two stories per year and that doesn't bring in a lot of visitors.

    -Wolf sends
  • Setnom
    Remember what the article says:

    this information could be important in helping researchers to better choose which exoplanets they might want to study or where they might send probes in the future.

    This is ground-laying work for the future. It's this type of "may be" science that will better inform and guide future exoplanet surveys with next-generation telescopes. Observing time is costly and therefore it's better to have a list of potential good targets than to "blindly" point these instruments.
  • rod
    FYI, here is the paper and abstract on this exoplanet study. Forecasting Rates of Volcanic Activity on Terrestrial Exoplanets and Implications for Cryovolcanic Activity on Extrasolar Ocean Worlds, "...we estimate total internal heating rates for 53 exoplanets with masses and radii up to ~8M ⊕ and 2R ⊕, respectively, assuming that internal heating is drawn from both radiogenic and tidal sources."

    An 8 earth mass exoplanet with radius 2 earth radii has mean density close to Earth's about 5.5 g cm^-3. Another report on this study says, "Some have suggested that some of these planets could be watery, and Quick's estimates support this idea. According to her team's calculations, TRAPPIST-1 e, f, g and h could be ocean worlds, which would put them among the 14 ocean worlds the scientists identified in this study.", https://phys.org/news/2020-06-planets-oceans-common-galaxy-nasa.html

    TRAPPIST-1 e is listed a bit larger than 0.6 earth masses orbiting a red dwarf star, http://exoplanet.eu/catalog/trappist-1_e/, and, https://exoplanetarchive.ipac.caltech.edu/cgi-bin/DisplayOverview/nph-DisplayOverview?objname=TRAPPIST-1+e&type=CONFIRMED_PLANET
  • dfjchem721
    While much is made of salt water oceans in the outer moons of our solar system, one needs to appreciate that the salt alone is not going to keep the water liquid at extremely low temperatures. Saturated sodium chloride only brings the freezing point of water down to ca. -30C or so.

    Since Enceladus has a surface temperature of about −198 °C, it is a pretty sure bet that liquid water is not going to exist on its surface, so how could it be liquid under the surface? Heating by tidal forces seems most likely, and salt could also play a role in this liquidity, but seemingly not by very much.

    To be sure, high salt would not only fail to provide the freezing point depression required for liquid water in very cold places, it also increases ion concentrations and their activity to higher levels that would be unlikely to support the origin of life. Brine, for instance, is ~ saturated salt in water, and is not a viable environment for most life on earth. Any life that does exist in brine almost certainly evolved into it, such as brine shrimp, a very rare example. It is highly probable that high concentrations of salt would be detrimental to kick-starting life, much less allowing it to evolve. More complex life forms have more demanding chemistries in order to thrive and persist.

    There seems little doubt that there are many worlds with oceans both above and below the surface, and many are likely within the Goldilocks Zone (GZ). But there is much more to that GZ that is required for abiogenesis. As should be obvious, all of the parameters for the origin of life have yet to be determined, but extremes should be ruled out for initial conditions.

    Again, life existing in extreme conditions likely evolved into those conditions. The earliest life forms would almost certainly have required milder environments in which to arise. And even if you have liquid water at low temperatures, the organic reactions required for abiogenesis would be unlikely to have the activation energy to produce those larger, more complex chemical forms required for life.

    Not too hot, and not too cold. And not too many salts, please, and it might be just right!
  • rod
    Interesting. We have an exoplanet study report here modeling exoplanets from 0.6 earth masses to 8 earth masses and little is factually known about them. There are many exoplanets documented that are in the wrong place, e.g. https://phys.org/news/2020-06-young-giant-planet-clues-formation.html. There are other exoplanets reported near 0.95 earth radii, but in the wrong place too, http://exoplanet.eu/catalog/epic_249631677_b/ with potential surface temperature 460 K. In various exoplanet reports and the scanty properties actually confirmed about them today, various extrapolations for life arising on them appear out of thin air :)
  • lawrence
    Keep in mind everyone that there is life living among the asteroids. Now where did that life take hold from ? I am theorizing that the astroid was once part of a world with the right ingredients for life to take hold and what those were we cannot be certain because we only know our example for life. Who is to say there are not other kinds of life out there where high salt oceans and -60c (surface) and tidal forces to keep the water liquid could not produce life. The ideas and possibilities give me much excitement thinking about it.
  • Bigrob215275
    Admin said:
    Far-off alien planets covered in vast oceans might be common in our Milky Way galaxy, scientists find.

    Our Milky Way galaxy may be teeming with ocean worlds : Read more
    Scientists get more desperate to report alien life every day. IT IS A DEMONSTRATION OF HOW DISHONEST they are. Life exists on Earth NOT just because there is water but because it resolves over 150 Lottery like odds being won at the same time. Earth needs a Sun of the right size and Stability to be at the right distance with the right orbits and 150 supercritical issues with LIFE BEING POSSIBLE. To call yourself a scientist and suggest life because you believe water, liquid water is on a planet is what you would expect from someone who is <<Offensive language removed by moderator>>.
  • dfjchem721
    Bigrob215275 said:
    Scientists get more desperate to report alien life every day. IT IS A DEMONSTRATION OF HOW DISHONEST they are.

    The odds of winning 150 lotteries as a measure of life arising anywhere in the universe means that we do not exist. Or only by the most extraordinarily unlikely chance that life on earth is a one-off event, a highly unlikely probability in itself. But nowhere remotely close to the nearly infinite odds of winning all those lottos! Jeez....

    Surely no one really knows what the odds are. How could they? But if anyone is going to calculate the odds, it is likely scientists. After all, they give the world all those experimental results which yields technology that actually works, providing them a very high degree of credibility. Most people would agree that this eliminates any notions that scientists are dishonest, although there are the occasional crackpots, like most endeavors in human activities.

    Since so much of what scientists have discovered meshes in all things - biology, chemistry, physics, etc.. , it is hard to imagine they are desperate to do anything. Unless they need to publish in order to retain funding (that one is always a real pain!). But clearly they have to do something. And other life forms arising in the universe offers a reasonable subject for consideration, now that we know so much about life, and the universe. Well, at least for some of us......

    But it should be admitted that the life of an Astrobiologist has to be some rough sledding at times. What are their job options? Teaching the science is about all there is, which allows some time to study those odds for life, and maybe narrow them down to winning a couple of lotteries, or even one. Some of them are likely going to publish articles on such things, and the current concepts involved. It is what they do.

    To be sure, the conditions for abiogenesis are pretty exacting, but the odds of finding such places is certainly much greater than some have suggested. With trillions of galaxies and their countless star systems, and over 10 billion years of time for life to arise, the odds are actually very high that it happened in more than just one place.

    And very likely many times, in oceans of places!
  • Catastrophe
    Ted A Campbell said:
    Seems to me that there are too many articles here with "may be" alien life. There may be alien life. Is that news? I suppose it must sell. I'd prefer to see about 90% "is" stories rather than "may be" stories.
    Right on!
    Piggies may be flying by their windows right now??