We're pretty fond of Earth, a planet covered in exposed oceans, and we keep looking for far-off planets that might be similar and capable of hosting life. But instead of looking harder, scientists may have to look deeper.
That's one takeaway from a paper that suggests planets and moons with water hidden beneath their crust may be common in other solar systems and that they could potentially host life, "vastly expanding the conditions for planetary habitability and biological survival over time." The paper, presented this week by Southwest Research Institute planetary scientist S. Alan Stern, looks at what it calls interior water ocean worlds, or IWOWs (PDF link).
When it comes to ocean worlds in our own solar system, Earth is an outlier. Scientists are studying Jupiter's moon Europa and Saturn's moons Titan and Enceladus as places that are likely hiding liquid oceans underneath their crusts. Dwarf planet Pluto is also suspected of harboring an ocean under its icy shell.
IWOWs offer a layer of protection for water-dwelling 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 in a Southwest Research Institute statement on Tuesday.
That's good news for habitability, but not such good news for scientists seeking signs of life on distant worlds. "The same protective layer of ice and rock that creates stable environments for life also sequesters that life from easy detection," said Stern.
NASA is working on sending missions to Europa and Titan. The Europa Clipper will orbit the moon and try to determine if it could be favorable for life. The Dragonfly mission will involve flying a drone across Titan on a hunt for the building blocks of life. These missions could help tell us if we should be getting our hopes up for IWOWs in other star systems.
Earth isn't the only ocean planet in the universe, but it may be an oddball in that it flaunts its water rather than hiding it away.