As astronomers continue to search for potentially habitable planets orbiting other stars, some have also started to consider the possibility of habitable moons orbiting giant planets in such systems. Such exomoons could be the size of Mars, Earth, or even a few times larger, based on observations of similar large moons orbiting Jupiter and Saturn. A few scientific studies have demonstrated that exomoons should be expected in other planetary systems and could even be observable with the next generation of space telescopes.
I recently published a paper with co-author René Heller in Monthly Notices of the Royal Astronomical Society titled “Exploring exomoon atmospheres with an idealized general circulation model.” This study presents the first three-dimensional climate modeling of exomoon atmospheres. Exomoon atmospheres receive daily instellation from the host star of the planetary system, which would make them similar in climate to an Earth-like planet. But exomoons are also in synchronous rotation with the host giant planet (similar to the synchronous rotation of our moon around Earth). Exomoons therefore receive additional thermal energy at the top of their atmospheres from their host planet, in addition to the star. This configuration leads to a climate with warmer poles (a phenomenon known as “polar amplification”) and stronger dynamical energy transport.
Some exomoons atmospheres could enter a runaway greenhouse from the additional thermal energy of the host planet, but others should be able to maintain stable and potentially habitable atmospheres. Exomoons remain viable prospects in the search for life, and future astronomical surveys will gradually reveal the frequency of such worlds.