Scientists have confirmed that one of two new moons recently discovered orbiting Jupiter is the smallest ever found.
The tiny moon, helpfully but not stylishly named S/2010 J2, is just 2,000m in diameter.
First discovered in 2010 with another moon (S/2010 J1), itself under 3,000m in diameter, the satellites bring the total number orbiting Jupiter to 67.
By contrast our moon is more than 3,400km across.
Jupiter's largest moon is Ganymede, which has a diameter of 5262km - almost twice the size of our own moon.
Several of Jupiter's moons have atmospheres of their own, including Europa which has an iron core, a surface made of ice and an atmosphere made primarily of oxygen.
Since the discovery scientists from the University of British Columbia have spent months tracking and mapping the path of the moons, to check they were really what they appeared to be.
Estimating the size of such tiny objects at such a vast distance is tricky, so scientists have had to estimate based on their brightness.
The astronomers behind the find now say there could be dozens more similarly small moons orbiting Jupiter, which is the largest planet in our solar system.
"We had actually already reported measurements of the first moon from Feb. 27 and 28, 2003 to the Minor Planet Center eight years ago", said researcher Brett Gladman at the University of British Columbia.
"But observations over several months are required to prove that the object is orbiting Jupiter, and this moon was too faint for the 2003 surveys to consistently track."