The Mutual Occultation of Ganymede and Io
Jupiter is one of the least lonely planets in the Solar System, at least when it comes to natural satellites. 115 moons have been discovered orbiting Jupiter so far! (Saturn has the most with 293, but who’s counting.) Ganymede and Io, two of Jupiter’s Galilean moons, met in the sky on October 20th, 2026. Today’s video captures the meeting, with Ganymede briefly blocking Io from view. This event, when an astronomical object passes in front of another and either completely or partially blocks it, is called a mutual occultation. The mutual occultations of Galilean moons are rare to witness because they require Earth’s edge-on view of their orbits. This occurs once every 6 years when Jupiter reaches its equinox and appears less “tilted”. Ganymede is also casting its shadow on Jupiter’s right side. Any fictional Jovian species within the shadow would experience a solar eclipse!
As the shadows of Ganymede and Io dance in a silent, mutual occultation across the Jovian expanse, we witness a celestial ballet of gravity and light that underscores the intricate mechanics of planetary motion. This rhythmic alignment serves as a local reminder of the profound cosmic choreography occurring light-years away, where the distant world GJ 357 d orbits its red dwarf star at the edge of a fragile equilibrium. Though separated by 9.44 parsecs, both these Jovian moons and the frigid, potentially habitable GJ 357 d exist as vital data points in our grand quest to understand the diverse architectures of worlds capable of harboring life.