The search for extraterrestrial life: new discoveries on distant planets
The search for life outside our solar system has taken an important step forward thanks to a study conducted by NASA. Research suggests that 17 exoplanets could host liquid oceans beneath thick ice crusts, with potential jets of water vapor fueled by internal heat. This discovery could greatly expand the search for life in the universe, by comparing these exoplanets with Europa and Enceladus, two moons of our solar system known to have underground oceans.
The possibility of life on distant exoplanets
The search for extraterrestrial life typically focuses on exoplanets located in the star's “habitable zone,” a distance where temperatures allow liquid water to remain on their surface. However, it is possible for an exoplanet very far away to exist and still exist. Cold. An ocean exists under an ice crust if it has sufficient internal heat. This is the case of Europa, one of Jupiter's moons, and Enceladus, one of Saturn's moons, where there are underground oceans heated by tides resulting from the gravitational pull of the host planet and nearby moons.
Life In the Dark: Underground Oceans
These subterranean oceans could host life if they had other needs, as a source of energy and the elements and compounds used in biological molecules. On Earth, entire ecosystems thrive in the complete darkness at the bottom of the oceans near hydrothermal vents, which provide energy and nutrients.
“Our analyzes predict that these 17 worlds may have ice-covered surfaces but receive enough internal heat from the decay of radioactive elements and tidal forces from their host stars to maintain their inner oceans,” said Dr. Linai Quick of NASA's Goddard Space Flight Center. Greenbelt, Maryland. “Due to the amount of internal heat they experience, all the planets in our study would also exhibit cryovolcanic eruptions in the form of geyser-like jets.” Dr. Quick is the lead author of a paper recently published in Astrophysical Journal.
Insights into the formation and climate of exoplanets
The team looked at conditions on 17 confirmed exoplanets that are roughly the size of Earth but less dense, suggesting they may contain large amounts of ice and water rather than denser rock. Although the exact composition of the planets is still unknown, preliminary estimates of their surface temperatures from previous studies all indicate that they are much colder than Earth, suggesting that their surfaces may be covered in ice.
The study improved estimates of surface temperatures for each exoplanet by recalculating using known surface brightness and other properties of the Europa and Enceladus models. The team also estimated the total internal heating in these exoplanets by using the shape of each exoplanet's orbit to take the heat from the tides and add it to the heat expected from radioactivity. Estimates of surface temperature and “overall warming” provided the thickness of each exoplanet's ice sheet, as oceans cool and freeze on the surface while being heated from within. Finally, they compared these numbers with those for Europa and used the estimated levels of geyser activity on Europa as a conservative basis for estimating geyser activity on exoplanets.
A new perspective on the temperatures and activity of exoplanets
They expect surface temperatures to be colder than previous estimates by up to 60 degrees Fahrenheit (about 33 degrees Celsius). Estimated ice sheet thickness ranges from about 58 meters for Proxima Centauri b and 1.6 kilometers for LHS 1140 to 38.6 kilometers for MOA 2007 BLG 192Lb, compared to the average European estimate of about 29 kilometers. Estimated geyser activity ranges from just 8 kilograms per second for Kepler 441b to 290,000 kilograms per second for LHS 1140 to 6 million kilograms per second for Proxima Centaurib, compared to Europa's 2,000 kilograms per second.
Detection of extraterrestrial geysers
“Since our models predict that oceans could be found relatively close to the surfaces of Proxima Centauri b and LHS 1140 b, and that their rate of geyser activity could exceed that of Europa by hundreds or thousands of times, geological telescopes are more likely to detect them.” Activity on these planets,” said Dr. Quick, who presented this research on December 12 at the American Geophysical Union meeting in San Francisco, California.
This activity can be seen when the exoplanet passes in front of its star. Some of the “starlight” colors may be obscured or obscured by the water vapor emitted by the geysers. “Sporadic water vapor detections, where the amount of water vapor detected varies over time, may indicate the presence of cryovolcanic eruptions,” Dr. Quick said. Water may contain other elements and compounds that can reveal whether it can support life. Because elements and compounds absorb light with specific “characteristic” colors, analyzing starlight will allow scientists to determine the geyser's composition and assess the habitability of the exoplanet.
For planets like Proxima Centauri b that do not pass through their stars from our perspective, geyser activity can be detected with powerful telescopes that can measure the light reflected by the exoplanet as it orbits its star. The geysers will spew icy particles onto the exoplanet's surface, making the exoplanet appear very bright and reflective.
The research was funded by NASA's Habitable Worlds Program, the University of Washington's Astrobiology Program, and the Virtual Planetary Laboratory, a member of the NASA Nexus Coordinating Group for Exoplanet System Science.
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