NASA researchers say they have identified 17 potentially habitable icy worlds that are approximately Earth-sized, including two that reside in our cosmic backyard.
Similar to the icy moons of Jupiter (Europa) and Saturn (Enceladus) in our solar system, these worlds are believed to contain massive oceans underneath an icy outer shell, where a combination of tidal forces and radiation might enable the types of life found in the deepest parts of Earth’s oceans.
The researchers also said that these icy worlds may contain surface geysers that erupt some of that water into space, where human-made telescopes could scan those plumes for signs of extraterrestrial life.
Dating back to the discovery of the first exoplanet in 1995, most efforts to search for life on other planets have focused on rocky worlds like Earth that orbit within their host star’s habitable zone, where temperatures would permit liquid water to exist on the planet’s surface. That’s because virtually all life on Earth uses liquid water, and Earth is the only place we have definitively found life.
For a long time, it was also believed that virtually all life forms required sunlight. However, recent discoveries of life forms in the deepest parts of Earth’s oceans that thrive in complete darkness have changed those calculations.
Dubbed “extremophiles,” these hardy organisms replace the light energy most life forms receive from the sun with thermal energy spewed by volcanic vents on the ocean floor. They also receive vital nutrients and other organic compounds from these vents, both of which are also critical to life.
These discoveries have led astrobiologists to redefine where they search for life outside Earth. Two of the most tantalizing targets are Europa and Enceladus. Scientists theorize that the tidal forces of their host planets and other moons combined with radiation energy generate enough internal heat energy that these icy moons may have oceans of seawater beneath their icy shells.
In 2005, NASA’s Cassini mission spotted geysers of water erupting from the surface of Enceladus, lending strong support to those theories. The space agency is even evaluating missions designed to fly spacecraft through those plumes and collect samples of the oceans below.
Hellbound and Down 