NASA is focusing its efforts on seeking extraterrestrial life in the Solar System and beyond. And life, as we understand it, depends on three main factors: liquid water, a source of energy for metabolism and the right chemical ingredients, mainly carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur. In the Solar System there are two possible ocean worlds that meet some of these requirements, necessary for a place to be habitable. Enceladus and Europa, two satellites of Saturn and Jupiter respectively, are the most reliable candidates, as revealed by NASA today. "We have never been so close to detecting a place with some of the ingredients necessary for an environment to be habitable," says Thomas Zurbuchen, a NASA astrophysicist.
Hydrogen gas, which could potentially provide a source of chemical energy for life, is distributed by the ocean that would be in the underground of Enceladus thanks to the hydrothermal activity of the seabed. If there were microbes then they could use hydrogen for energy by combining hydrogen with carbon dioxide dissolved in water. This chemical reaction called methanogenesis, because it produces methane as a byproduct, is at the roots of earthly life and could be crucial to the origin of life on Earth. The Cassini spacecraft has shown that Enceladus has almost all the necessary ingredients to be habitable; Phosphorus and sulfur have not yet been detected in the ocean, but scientists suspect that they might exist, since the rocky core of Enceladus appears to be chemically similar to meteorites that contain both elements.
On the other hand, some images taken by the Hubble Space Telescope indicate that the water vapor columns of Europe could be a real phenomenon, sprouting intermittently in the same region of the lunar surface. A new image shows a column that rises about 100 kilometers above the surface of Europe. Researchers believe that, as with Enceladus, this could be evidence that water is being expelled from inside the moon.
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