Public Domain Image, created by NASA. Original source: http://planetquest.jpl.nasa.gov/images/NEWextrasolar-medium.jpg
The above artist’s impression shows an imagined habitable moon in orbit around a gas giant planet in another star system: the bluish habitable moon (with liquid surface water and an atmosphere) in the foreground, the gas giant planet in its background, another moon visible to the left, and the system’s host star in the upper left.
Beyond our Solar System, many stars have been identified that are believed to have orbiting planets, and many planets have been identified that probably have one or more moons. Increasingly, moons in the solar system are considered attractive candidates for potentially harboring life, such as in subsurface liquid water. Could moons orbiting planets in other star systems also harbor life?
This artist’s impression shows a sunset (speculated and hypothetical) as seen from an exoplanet in another solar system – super-Earth Gliese 667 Cc, in a triple star system. Image Credit: ESO/L. Calçada. Source: http://www.eso.org/public/images/eso1214a/.
While candidates beckon even within our Solar System (particularly moons of other planets), so do the stars at night … and their potential planets and moons.
In this last regard, evidence continues to mount that some such star systems do indeed include planets (known as exoplanets), and that some of those planets host natural satellites, or moons (known as exomoons).
While there are many factors speculated to potentially influence planet and moon habitability, some key ones boil down to an assessment of the presence, or likely presence, of stable liquid water, the availability of energy accessible for life, and likely presence or potential formation of organic compounds.