In our Solar System, moons present some of the most intriguing phenomena, often more captivating than the planets they orbit. These celestial bodies exhibit a variety of features, including active volcanoes, vast seas of hydrocarbons, explosive geysers, and expansive subsurface oceans concealed beneath thick layers of ice. The processes governing the formation of large planets suggest that moon formation should be a natural outcome. Consequently, it is expected that our galaxy is home to a plethora of moons.
However, despite some promising evidence, researchers have yet to conclusively identify a moon orbiting an exoplanet. Instead, what has been observed are several young exoplanets that appear to possess disks conducive to moon formation. Recently, the James Webb Space Telescope has captured a spectrum of a ring-forming disk surrounding a massive super-Jupiter and found it to contain a significant quantity of small carbon-based molecules. This discovery is particularly intriguing given that the star it revolves around seems to have a planet-forming disk that is predominantly composed of water.
Finding disks
The methodologies for detecting exo-moons and moon-forming disks differ substantially. Identifying a moon relies on its gravitational effects. During certain phases of its orbit, a moon can affect its planet’s trajectory by hastening its orbit or slowing it down. This gravitational interaction creates minute variations in the timing of when the planet transits in front of its host star, as observed from Earth.
Additionally, a moon would also obscure a fraction more of the star’s light at various points in its orbit; however, this can easily be overshadowed by the natural variability of the star itself.
In contrast, moon-forming disks are a transient feature, only present during the formative years of an exoplanetary system. These disks resemble the rings of Saturn on a larger scale and contain sufficient materials to eventually form moons. Within the initial millions of years of a solar system’s evolution, the material in these disks is likely to either disperse, condense into moon bodies, or fall into the central planet.
