Jupiter’s Moons get an Update

Article written by: Heather Alexander, Education Officer

Space is always changing. New objects are discovered frequently, and the latest discovery was made inside our own Solar System. Jupiter, the largest planet in the Solar System, now has a staggering 79 moons in its orbit. Compare this to Earth’s lonely, singular moon and this shows you just how monstrous the gas giant planet is in size.

The cloud-covered face of Jupiter (Image credit: NASA)

The discovery was made last year by a team of astronomers (The Carnegie Team) who were on the look out for planets lying beyond Pluto. While observing a particular area of the sky, Jupiter just so happened to be in the same sightline and so they turned their attention to the gas giant, as well as continuing their search for other planets on the fringe of our solar system. It took a whole year to confirm the objects they discovered are actually orbiting around Jupiter, but now that confirmation has come about, the total number of moons has risen to an impressive 79!

Initially the astronomers thought that some of these moons could be a cluster of asteroids passing by the gas planet, however they were upgraded to moons. They orbit Jupiter in the opposite direction, or retrograde, to its spin rotation and are nine in total. It is speculated that these small moons are the remnants of three massive moons which were broken apart by collisions with other bodies in space.

Two of the new moons are much closer to Jupiter and orbit in the same direction as the planet’s rotation, or prograde. They are also believed to be part of a larger moon, which had broken apart.

Image depiciting the prograde orbits of the strange moon “Valetudo”, which is found amongst the retrograde moons. (Image Credit: Carnegie Institute of Science/Roberto Molar Candanosa)

The final moon is the one that has astronomers really excited. This strange, oddball moon, which has so far been named Valetudo, is found orbiting with the retrograde moons, but it itself is orbiting in a prograde orbit. Highly unusual, and very exciting. The best way to think about it is to imagine driving a car the wrong way up a motorway. There are lots of objects in its way and eventually it is likely it will have a head on collision with one of them. The name Valetudo comes from the great-granddaughter of the Roman God Jupiter. She was the goddess of Health and Hygiene.

We still don’t know an awful lot about these new moons, like what they look like or what they’re made of. NASA’s Juno spacecraft, which is currently orbiting Jupiter, is not in a position to image them. It will take a future mission to Jupiter to get a clearer view of them. The only things we know right now are their approximate sizes and the shape of their orbits.