'Breakneck speed' mini moon hurtles around Neptune at 20,000mph

Astronomers confirm orbit of tiny moon Hippocamp via multiple images from Hubble

A miniature moon that whizzes around Neptune at breakneck speed has been tracked by astronomers working from the US.

The speck of a moon, no more than 21 miles across, hurtles around the distant gas giant at about 20,000 miles an hour, 10 times faster than our own moon circles Earth, scientists said.