On Titan, Saturn’s largest moon, it rains on a regular basis. As with Earth, these rains are the result of liquid evaporating on the surface, condensing in the skies, and falling back to the surface as precipitation. On Earth, this is known as the hydrological (or water) cycle, which is an indispensable part of our climate. In Titan’s case, the same steps are all there, but it is methane that is being exchanged and not water.
In recent years, scientists have found evidence of similar patterns involving exoplanets, with everything from molten metal to lava rain! This raises the question of just how exotic the rains may be on alien worlds. Recently, a team of researchers from Havard University conducted a study where they researched how rain would differ in a diverse array of extrasolar planetary environments.
This research was conducted by Kaitlyn Loftus, a Ph.D. student from Harvard’s Department of Earth and Planetary Sciences. Her supervising professor (and co-author on the study) was Robin D. Wordsworth, who leads the Wordsworth Planetary Climate and Atmospheric Evolution Research Group at Harvard’s School of Engineering and Applied Sciences (SEAS).
Research into precipitation and records of past rainfall on Earth has taught scientists a great deal about the dynamical nature of its climate. Unfortunately, this same research is not yet possible with exoplanets, which prevents scientists from being able to place tighter constraints on their potential habitability. However, knowledge of these conditions on Earth has helped scientists to predict planetary climates Mars, and Titan.
For the sake of their study, Loftus and Wordsworth examined how this could be applied to exoplanets as well. As Loftus explained to Universe Today via email:
“A key component of habitability is climate (to test whether a planet can support liquid surface water). A major driver of uncertainty in understanding climate in different planetary environments (even, say, the current transition of modern Earth to higher CO2 levels) is how clouds behave. Precipitation is a key way clouds “die,” so understanding how precipitation works can help us constrain cloud behaviors and eventually better predict planetary climate.
“Precipitation additionally helps control how much water stays in an atmosphere. As water vapor is a very good greenhouse gas, this balancing of how much water is in an atmosphere can also impact climate... Finally, rainfall is an essential component of the negative feedback mechanism to stabilize planetary climates (the carbonate–silicate cycle) that underlies the concept of the exoplanet “habitable zone.”
Read more:: How Would Rain be Different on an Alien World?