One of the most ground-shaking discoveries planetary scientists have made in the last 25 years is how worlds with hidden oceans beneath layers of ice and rock are a common feature of our solar system. These worlds include icy satellites of gas giant planets like Enceladus, Titan, and Europa. Pluto is also suspected to house a secret underground ocean.
However, the prevalence of interior water ocean worlds (IWOWs) in our solar system implies this prevalence might extend to other solar systems — substantially expanding the conditions for planetary habitability and biological survival, not least of which because underground oceans don't need to be within a host star's habitable zone to support life, according to a presentation at the 52nd annual Lunar and Planetary Science Conference (LPSC-52) this week and shared in a ScienceDaily report.
Interior water ocean worlds could shield life from the dangers of space
Scientists have known for a long time how worlds like ours — with surface oceans — need to orbit host stars within a narrow range of distances to regulate atmospheric temperatures and maintain liquid oceans. But IWOWs are found over a much broader scope of distances from their host stars, multiplying the number of possibly habitable worlds in the universe far above earlier estimates.
Earth-like worlds with oceans on the outside must also face unyielding threats to life — including stellar flares with deadly radiation, asteroid and comet impacts, nearby supernova explosions, and many more. Planetary Scientist S. Alan Stern — who presented the report — said IWOWs are immune to these cosmic threats because their oceans feature a solid and protective roof of rock and ice, generally several to many tens of miles thick — shielding entire oceans from external threats to life.
"Interior water ocean worlds are better suited to provide many kinds of environmental stability, and are less likely to suffer threats to life from their own atmosphere, their star, their solar system, and the galaxy, than are worlds like Earth, which have their oceans on the outside," said Stern during his report.
Life on interior water ocean worlds is virtually impossible to detect remotely
Stern also said the same protective layer of rock and ice shielding the oceans on IWOWs also conceal any resident life-forms from remote detection via nearly all astronomical techniques. If worlds with underground oceans are the primary habitat for life in the galaxy — and they also enable the rise of intelligent life — then IWOWs could also help astronomers crack the Fermi Paradox.
The Fermi Paradox is an idea addressing the apparent discrepancy between the statistical likelihood of life in our universe and the deafening silence from our continued search — via the Search for Extraterrestrial Intelligence, analyzing exoplanet atmospheres, physical interstellar probes like Voyagers 1 and 2, and more.
In essence, the Fermi paradox reflects the perspective of the late physicist Enrico Fermi who, while working at Los Alamos National Laboratory in 1950, asked the big question about life in the universe: "Where is everybody?"
If life can and does exist in interior water ocean worlds, and conditions in deep oceans are ripe for intelligence — and we can't stress enough how big this "if" is — then Stern may have an answer as to why the universe seems so empty. "The same protective layer of ice and rock that creates stable environments for life also sequesters that life from easy detection," said Stern.