New Theory Emerges on the Formation of Jupiter’s Galilean Moons

Jupiter’s moon Io imaged in front of the planet’s clouds by NASA’s Galileo spacecraft on Sept. 6, 1996. According to a new model, volcanic Io (and its icy neighbor Europa) were the first of Jupiter’s moons to form. Credit: NASA/JPL-Caltech/Jason Major

During the first few million years of our sun’s lifetime it was surrounded by a protoplanetary disk made up of gas and dust. Jupiter coalesced from this disk and became encircled by its own disk of satellite-building material. This “circum-Jovian disk” was fed by material from the sun’s protoplanetary disk that rained down on Jupiter at the planet’s poles, and flowed back out of Jupiter’s gravitational influence along the planet’s equatorial plane. But this is where things get tricky for satellite formation; how did this ever-changing disk accumulate enough material to form moons?

*The surface of Ganymede, Jupiter’s largest moon, imaged by Galileo in February 1997. NASA/JPL-Caltech/Jason Major*

Now, Caltech professor of planetary science Konstantin Batygin and his collaborator Alessandro Morbidelli of Observatoire de la Côte d’Azur in France have proposed an answer to this longstanding question. Using analytical calculations and large-scale computer simulations, they propose a new theory of the Jovian satellites’ origins.

(And in a very classical-physicist style, the inspiration for the theory came to Batygin while he was out for a jog!)