Arche’s size and shape
Arche is the 39th largest moon of Jupiter with a diameter of 1.9 miles, making it about 4200 times smaller than Earth. Arche has a light red color and although scientists aren’t sure, its small size means that it does not have a strong enough gravity to form itself into a sphere. This means that shape of Arche is probably an irregular blob.
Arche orbits around Jupiter at a distance of about 15 million miles, which is the 9th farthest from Jupiter. This moon travels around Jupiter at a speed of 5000 miles per hour, 13 times slower than Earth. It takes about 732 Earth days to complete its orbit, which is the 15th longest orbital time of all of Jupiter’s moons.
Arche is in a group of Jupiter moons called the Carme group
All of the moons in this group are similar and scientists think they all came from an asteroid collision that split apart into about two dozen new moons. Because Jupiter is so large and its gravity is so strong, asteroids and comets that are traveling by sometimes get caught and collide with other objects around Jupiter. This is probably how Arche was formed. Due to this strange origin, all of the moons in Arche’s group have an odd orbit around Jupiter. Arche orbits in the opposite direction that Jupiter spins. This is called a retrograde orbit and its why Arche’s name ends in an “e”.
All of the Jupiter moons with a retrograde orbit end in an “e”. Arche also has an orbit that is much more like an oval than a circle. This is called a highly eccentric orbit and it means that Arche changes from being close to Jupiter sometimes and being much farther away from Jupiter at other times. Finally, Arche orbits at a much different angle than most of the other moons of Jupiter.
Arche was discovered in 2002
The discovery of Arche happened in 2002, four hundred years after Galileo first discovered Jupiter’s largest moons around the year 1600. Galileo used a small telescope to see these large moons and it wasn’t possible to see moons as small as Arche. To see it, Astronomers needed a very large and sophisticated telescope on top of a mountain in Hawaii. Not much is known about the surface of Arche because scientist’s have never sent any probes and have only observed it from long distances away.
Arche’s future is unknown
There is one moon in Arche’s Carme group that may one day smash into it and end Arche’s existence as a moon of Jupiter. Valetudo is another moon in the same group as Arche but it is orbiting in the opposite direction. This is like two cars traveling towards each other in the same traffic lane, eventually they will collide. Scientists don’t know when this will happen or if Valetudo will collide with Arche or another moon from the Carme group. Eventually, however, a collision will probably occur, and it may destroy Arche forever.