How long did it take to establish the water content within Jupiter’s Galilean moons, Io and Europa? This is what a recent study published in The Astrophysical Journal hopes to address as a team of scientists from the United States and France investigated the intricate processes responsible for the formation and evolution of Io and Europa. This study has the potential to help scientists better understand the formation and evolution of two of the most unique moons in the solar system, as Io and Europa are known as the most volcanically active body in the solar system and an ocean world estimated to contain twice the volume of Earth’s oceans, respectively.
For the study, the researchers used a series of models to simulate the early formation history of Io and Europa billions of years ago, which occurred when Jupiter was much brighter than today. The goal of the study was to ascertain how Io lost its water whereas Europa gained large amounts of it. The researchers suggested both moons initially had water but atmospheric escape cause Io to lose its water while Europa retained its water.
In the end, the researchers proposed that instead of both moons forming with water and Io later losing its water, that Io initially formed without water while Europa formed with water. Essentially, the present-day environments on both moons were established during their initial respective formations.
The study notes, “Despite the assumptions adopted in this work, Io was likely unable to lose its initial water inventory. After the dissipation of the accretion disk and the fading of Jupiter’s luminosity, the residual ice shell would not have been removed by tidal heating over geological timescales. This suggests that Io accreted primarily anhydrous [non-water] silicates and that the compositional contrast between the two inner moons reflects the thermodynamic structure of Jupiter’s CPD [circumplanetary disk] at the time of their formation, rather than divergent evolutionary or atmospheric loss processes.”
While Ganymede and Callisto comprise the third and fourth Galilean moons, respectively, the researchers note they were not included in this study for numerous reasons. These include higher surface gravities, colder formation from the greater distances from Jupiter, and the decreased tidal forces that are substantially stronger on Io and Europa. Unlike Io and Europa, Ganymede and Callisto’s are comprised of much larger amounts of ice, and the decreased tidal forces from Jupiter has enabled both moons to retain a primarily icy state, unlike the more active Io and Europa.
The tidal forces enacted on Io and Europa come from the constant stretching and compressing that both moons experience as they orbit the much larger Jupiter, with their orbits being somewhat elliptical (oval-shaped). When they are closer to Jupiter, they are stretched by its massive gravity and are subsequently compressed as they travel farther away from Jupiter. This phenomenon is also called tidal flexing, and it results in the interiors of both moons heating up from friction over great timescales, with Io being volcanically active and Europa containing a large body of salty liquid water.
“Io and Europa are next-door neighbors orbiting Jupiter, yet they look like they come from completely different families,” said Dr. Olivier Mousis, who is a planetary scientist at the Southwest Research Institute and a co-author on the study. “Our study shows that this contrast wasn’t written over time — it was already there at birth.”
This study comes as NASA’s Europa Clipper is currently en route to Europa to study its potential habitability, with an estimated arrival date of April 2030. During its scheduled 4-year mission, Clipper is slated to conduct approximately 50 close flybys of Europa using elongated orbits. The reason for this is so the spacecraft doesn’t stay in Jupiter’s massive magnetic field for too long, and its intense radiation could damage the spacecraft components and compromise the mission.
What new insight into Io and Europa’s formation and evolution will researchers make in the coming years and decades? Only time will tell, and this is why we science!
As always, keep doing science & keep looking up!
