In a boost to finding alien life, NASA scientists have discovered that oceans beneath the icy surface of distant worlds at the edge of our solar system may sustain liquid water for far longer than previously believed.
This greatly expands the number of locations where extraterrestrial life might be found, since liquid water is necessary to support known forms of life and astronomers estimate there are dozens of these worlds, researchers said.
Heat generated by the gravitational pull of moons formed from massive collisions could extend the lifetimes of liquid water oceans beneath the surface of large icy worlds in our outer solar system.
"These objects need to be considered as potential reservoirs of water and life," said Prabal Saxena of NASA's Goddard Space Flight Center in the US.
"If our study is correct, we now may have more places in our solar system that possess some of the critical elements for extraterrestrial life," said Saxena, lead author of the research published in the journal Icarus.
These frigid worlds are found beyond the orbit of Neptune and include Pluto and its moons. They are known as Trans- Neptunian Objects (TNOs) and are far too cold to have liquid water on their surfaces, where temperatures are below minus 200 Celsius.
However, there is evidence that some may have layers of liquid water beneath their icy crusts.
In addition to bulk densities that are similar to other bodies suspected to have subsurface oceans, an analysis of the light reflected from some TNOs reveals signatures of crystalline water ice and ammonia hydrates.
At the extremely low surface temperatures on these objects, water ice takes a disordered, amorphous form instead of the regularly ordered crystals typical in warmer areas, such as snowflakes on Earth.
Space radiation converts crystalline water ice to the amorphous form and breaks down ammonia hydrates, so they are not expected to survive long on TNO surfaces.
This suggests that both compounds may have come from an interior liquid water layer that erupted to the surface, a process known as cryovolcanism.
The new research found that the gravitational interaction with a moon can generate enough additional heat inside a TNO to significantly extend the lifetime of a subsurface ocean.
"We found that tidal heating can be a tipping point that may have preserved oceans of liquid water beneath the surface of large TNOs like Pluto and Eris to the present day," said Wade Henning of NASA Goddard and the University of Maryland in the US.
"Crucially, our study also suggests that tidal heating could make deeply buried oceans more accessible to future observations by moving them closer to the surface," said Joe Renaud of George Mason University.
"If you have a liquid water layer, the additional heat from tidal heating would cause the next adjacent layer of ice to melt," Renaud said.
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