NASA: Some Icy Exoplanets May Have Habitable Oceans and Geysers

A NASA research suggests that 17 exoplanets—worlds outside of our solar system—may contain liquid water seas beneath their ice shells, which would further the hunt for extraterrestrial life. Sometimes, as geysers, water from these seas may burst through the ice crust. For the first time, estimations of the quantity of geyser activity on these exoplanets were determined by the scientific team. They found two exoplanets that were close enough for telescopes to detect evidence of these eruptions.

Typically, exoplanets in a star's "habitable zone," or the distance at which temperatures let liquid water to remain on their surfaces, are the focus of searches for extraterrestrial life. If an exoplanet has adequate internal warmth, it might be able to support an ocean beneath its ice shell even if it is too far away and too cold. This is the situation in our solar system, where the tides from the host planet's and its surrounding moons' gravitational pull enable the deep seas of Europa, a moon of Jupiter, and Enceladus, a moon of Saturn, to exist.

If these subterranean waters include additional essentials like an energy source and elements and chemicals that are employed in biological molecules, they may support life. Whole ecosystems on Earth flourish in total darkness around hydrothermal vents, which supply energy and nutrients, at the bottom of seas.

According to Dr. Lynnae Quick of NASA's Goddard Space Flight Center in Greenbelt, Maryland, "our analyses predict that these 17 worlds may have ice-covered surfaces but receive enough internal heating from the decay of radioactive elements and tidal forces from their host stars to maintain internal oceans." All of the planets in our analysis may also show cryovolcanic eruptions in the form of plumes resembling geysers due to the degree of internal heating.” A publication on the subject was published on October 4 in the Astrophysical Journal, with Quick serving as the primary author.

The scientists took into account the circumstances on 17 verified exoplanets that are smaller than Earth but have lower densities, indicating that they could have significant amounts of water and ice rather than harder rock. The precise compositions of the planets are yet unknown, but preliminary findings from earlier research on their surface temperatures all point to temperatures far lower than Earth's, raising the possibility that ice may be covering their surfaces.

The surface temperature estimates of each exoplanet were recalculated using models based on the known surface brightness and other characteristics of Europa and Enceladus, which led to better estimations. Additionally, the scientists calculated the overall interior heating of these exoplanets by combining the heat predicted from radioactive activity with the heat created by tides derived from the orbital shape of each exoplanet. Since the oceans cool and freeze at the surface while being heated from the inside, estimations of the surface temperature and total heating provided the thickness of the ice layer for each exoplanet. Lastly, they contrasted these numbers with those of Europa, using the latter's predicted geyser activity levels as a conservative starting point for estimating the exoplanets' geyser activity.

According to their predictions, surface temperatures might be up to 60 degrees Fahrenheit (approximately 33 degrees Celsius) lower than earlier forecasts. In comparison to Europa's estimated average of 18 miles (almost 29 kilometers), the estimated ice shell thickness ranged from roughly 190 feet (58 meters) for Proxima Centauri b and one mile (1.6 kilometers) for LHS 1140 b to 24 miles (38.6 kilometers) for MOA 2007 BLG 192Lb. In comparison to Europa, which had geyser activity of 4,400 pounds per second (2,000 kilograms per second), the estimated geyser activity for Kepler 441b was only 17.6 pounds per second (about 8 kilograms per second), but for LHS 1140 b and Proxima Centauri b it was 639,640 pounds per second (290,000 kilograms/second) and 13.2 million pounds per second (six million kilograms/second).

Quick, who presented this research on December 12 at the American Geophysical Union meeting in San Francisco, California, stated, "Our models predict that oceans could be found relatively close to the surfaces of Proxima Centauri b and LHS 1140 b, and their rate of geyser activity could exceed Europa’s by hundreds to thousands of times." This means that telescopes are most likely to detect geological activity on these planets.

The exoplanet's motion may be observed when it passes in front of its star. The water mist from the geysers might obscure or dull some hues of starlight. According to Quick, sporadic observations of water vapor, where the amount of vapor recorded changes over time, would point to the possibility of cryovolcanic eruptions. Other substances and components in the water may indicate whether or not it can sustain life. Scientists might analyze the starlight to establish the composition of the geyser and assess the exoplanet's habitability prospects since different elements and compounds absorb light at unique hues known as its "signature."

Strong telescopes that can monitor light that an exoplanet reflects while circling its star may be able to detect geyser activity for planets like Proxima Centauri b that do not cross their stars from our point of view. At the exoplanet's surface, geysers would shoot frozen particles, giving the object a dazzling, shiny appearance.

The Virtual Planetary Laboratory, a collaborator on the NASA Nexus for Exoplanet System Science coordination group, the University of Washington's Astrobiology Program, and NASA's Habitable Worlds Program provided funding for the study.