Other than our very own blue marble, Earth, the best prospects for life on other heavenly bodies in our solar system might be Mars, Europa, Titan, Enceladus, Io, and Jupiter. Of course life as we know it cannot exist on any of these bodies. Mars is the most Earth-like of all the planets and it was even more Earth-like eons ago. Recent evidence of water on the red planet indicates that it had a very different past than the images and data we have collected in recent years.
Europa, one of the moons of Jupiter, almost certainly has liquid water beneath it’s icy surface. I recently watched an interesting and very speculative movie called “The Europa Report” about a team of astronauts whose mission was to explore the surface of Europa. The film was very reminiscent of “2001: A Space Odyssey”, evocative of what could be. Who knows what lies beneath the icy surface of Europa. Another moon of Jupiter, Io, has a very complex chemistry, which causes it to be much warmer than most other bodies in the outer solar system. Io is the fourth largest moon in the solar system. With over 400 active volcanoes, it is also the most geologically active object in the solar system. Io’s surface is dotted with more than 100 mountains that have been uplifted from the base of it’s silicate crust. Could there be a unique form of life dwelling on or beneath Io’s silicate rocks and sulfur plains? Jupiter itself might be a long shot candidate for life. It is a warm planet with plenty of organic material. A thick, hydrogen gas atmosphere makes it difficult to determine where atmosphere ends and planet begins. Composition of 78% of the planet is metallic hydrogen. Sandwiched between the hydrogen atmosphere and this molten surface lies a band of clouds, some composed of ammonia and some composed of water. Amino acids, basic building blocks of life, could be part of this cloud layer.
Titan, the largest moon of Saturn, has been described as a planet-like moon. It is primarily composed of water ice and rocky material. In 2004, the Cassini-Huygens probe discovered hydrocarbon lakes in Titan’s polar regions. Climate similar to that on Earth [including wind and rain] create surface features similar to those on our planet, such as dunes, rivers and lakes [although the lakes contain liquid methane and ethane rather than water]. It has been suggested that life on Titan might use liquid hydrocarbon, such as methane or ethane, in much the same way we use liquid water. Perhaps five billion years from now, when our sun becomes a red giant and ultraviolet output decreases, Titan could be transformed into an Earth-like habitat.
Enceladus, the sixth-largest moon of Saturn seems to have liquid water beneath its icy surface. Cryovolcanoes at the south pole shoot large jets of water vapor and some solid NaCl particles into space. Some of this water falls back to the surface. Some of it becomes part of the rings of Saturn. Because of this apparent water at or near the surface, Enceladus may be the best place for humans to look for extraterrestrial life.None of the planets and moons that I have mentioned here are very good prospects for life and there are great arguments that life cannot exist on any of them. Could there be life on other planets, orbiting other suns, in some far distant corner of the galaxy? Your guess is as good as mine. The only things of which we can be certain are that we don’t know and we need to seek more evidence.
