Details of Jupiter’s smallest known moon have been unveiled. The moon, S/2012  J 2, was discovered in September 2010 along with one other moon called S/2010 J1.. The moon has a diameter of about 1.2 miles (2 kilometers), wile S/2010 J 1 is about 1.8 miles.

S/2010 J 1 is now known to be circling Jupiter at a average didtance of 14.57 million miles. This takes it 2.02 earth years to complete a lap aound it. Wile S/2010 J 2 only takes 1.69 earth years to go around Jupiter, at a  average distance of 13.06 million miles.

“It was exciting to realize that this [S/2010 J 2] is the smallest moon in the solar system that was discovered and tracked from Earth,” said co-author Mark Alexandersen, of the University of British Columbia, in a statement.

Jupiter is surrounded by 50 main moon that have names, and at least 14 smaller provisional moons that are known only by their numbers.