In recent years, extrasolar moons, or exomoons, have become exciting to astronomers because of the myriad of properties they could exhibit that we don’t see in our solar system. In fact, exomoons may soon become leading candidates in the search for extraterrestrial life.
As is often the case in scientific research, the greatest challenge in studying exomoons may actually be what makes them most interesting: no one has ever physically observed one.
The most cutting-edge telescopes today have trouble detecting even the largest exoplanets. As a result, most known exoplanets are Jupiter-like gas giants orbiting closer to their star than Venus does to our Sun. At such close distances, the tidal forces acting on a planet by its parent star are powerful enough to strip off any potential exomoons.
Recent advances in instrumentation are, howeer expanding the range of detectable exoplanets. The detection of smaller planets on wider orbits that could potentially support exomoons is now becoming more and more feasible.
In addition to the challenge astronomers face actually observing exoplanets exomoons, there are limitations regarding the types of stars that astronomers are able to find extrasolar bodies orbiting. It turns out to be easiest to detect planets orbiting red dwarfs- small, dim, cool stars that generally emit <1/100th the light that our Sun does. For an exoplanet orbiting such a star to be potentially habitable, it would have to orbit very close- so close that it would become tidally locked to its star. Tidal locking, a phenomenom that occurs due to spin-orbit interactions, means that one side of the planet woud always face away, and one side always toward the star. This would in effect create a very unhabitable situation in which half the planet’s surface would be in a deep freeze and half scorching hot.
An exomoon, however, offers an alternative scenario. Since exomoon orbits are relatively independent of their star, they are not necessarily subject to tidal locking at very close ranges. An exomoon orbiting a tidally-locked planet could avoid tidal locking, and furthermore be positioned at just the right distance from a weak star to generate habitable surface conditions.
Exomoons, which have until recently been a thought-experiment made of complex equations and astronomer’s dreams, may become reality as telescopes probe deeper and more discerningly into the fabric of unknown space.
—-The author would like to credit astronomer Nicholas Stone for providing valuable information on current research and theory regarding exomoons