Neptune moon: Archival images from the Hubble Space Telescope has revealed a tiny, faint moon orbiting Neptune, bringing the distant gas giant's known moons to 14.
NASA, ESA, and M. Showalter (SETI Institute)
The newfound Neptune moon — called S/2004 N 1 — was discovered July 1 during a fresh analysis of older Hubble Space Telescope images, scientists said. The newly discovered satellite is Neptune's smallest known moon and is just 12 miles (19 kilometers) wide.
Hubble telescope scientists announced the new Neptune moon's discovery today (July 15). The small satellite wasn't easy to find. [See Photos of Neptune, The Mysterious Blue Planet]
"The moons and arcs [segments of rings around the planet] orbit very quickly, so we had to devise a way to follow their motion in order to bring out the details of the system," SETI Institute scientist Mark Showalter, the moon's discoverer, said in a statement. "It's the same reason a sports photographer tracks a running athlete — the athlete stays in focus, but the background blurs."
In order to find the moon, Showalter dug through archival photos taken by Hubble from 2004 to 2009. The newly found moon appears in about 150 of those photos. By plotting a circular orbit of the moon, Showalter saw that the tiny satellite fully orbits Neptune every 23 hours.
The tiny moon is so small and hard to see that it even evaded NASA's Voyager 2 spacecraft when it flew by Neptune in 1989. At the time, Voyager 2 revealed six previously unknown moons in orbit around the blue planet, NASA officials have said.