Our galaxy may be full of ocean worlds, some of which could support life

Planets with liquid oceans may be common in our galaxy, according to new research, enlarging the pool of potentially habitable exoplanets for us to explore.

Researchers from NASA’s Goddard Space Flight Center, the Planetary Science Institute, and the University of Idaho wanted to know whether any of the currently known exoplanets (numbering more than 4,200) could have oceans. However, these planets are too far away to be observable in detail. So they used information on the planets’ sizes, masses, and distance from their stars to estimate their conditions.

The researchers looked at the properties of 53 known exoplanets which are a similar size to Earth, including those in the famous TRAPPIST-1 system, and calculated how likely each was to have volcanic activity, which is linked to how habitable a planet could be. Too much or too little volcanic activity can create inhospitable conditions for the existence of water and therefore life.

So they looked at planets which had an appropriate amount of volcanic activity, and found that over a quarter, or 26%, of the planets they looked at could be ocean worlds, meaning a planet with a current liquid ocean (although not necessarily one which covers the entire planet).

Some of these worlds may have liquid oceans beneath a layer of surface ice, similar to icy moons in our solar system like Saturn’s moon Enceladus or Jupiter’s moon Europa. Even though these moons don’t have atmospheres, they are still potentially capable of supporting life.

This illustration shows NASA's Cassini spacecraft flying through plumes on Enceladus in October 2015.
This illustration shows NASA’s Cassini spacecraft flying through plumes on Enceladus in October 2015. NASA/JPL-Caltech

“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,” NASA planetary scientist and lead author Lynnae Quick explained in a statement. “So if we’re thinking about these places as being possibly habitable, maybe bigger versions of them in other planetary systems are habitable too.”

This means that ocean worlds could be common in our galaxy, and provide many options for planets to explore which are potentially capable of supporting life. The research also suggests that the places where we look for life could be expanded to different types of bodies.

“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 astrophysicist and one of the co-authors of the research explained in the 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.”

The findings are published in the journal Publications of the Astronomical Society of the Pacific.

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