WASHINGTON, July 15 (Xinhua) -- U.S. space agency NASA said Monday its Hubble Space Telescope has found a new moon orbiting the distant blue-green planet Neptune, the 14th known to be circling the giant planet.
The moon, designated S/2004 N 1, is estimated to be no more than 12 miles (19 kilometers) across, making it the smallest known moon in the Neptunian system, NASA said.
It is so small and dim that it is roughly 100 million times fainter than the faintest star that can be seen with the naked eye, and it even escaped detection by NASA's Voyager 2 spacecraft, which flew past Neptune in 1989 and surveyed the planet's system of moons and rings, the agency said.
Mark Showalter of the U.S. nonprofit science research group SETI Institute found the moon on July 1, while studying the faint arcs, or segments of rings, around Neptune.
"The moons and arcs orbit very quickly, so we had to devise a way to follow their motion in order to bring out the details of the system," he 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."
The method involved tracking the movement of a white dot that appears over and over again in more than 150 archival Neptune photographs taken by Hubble from 2004 to 2009.
Showalter noticed the white dot about 65,400 miles (one million kilometers) from Neptune located between the orbits of the Neptunian moons Larissa and Proteus. Showalter plotted a circular orbit for the moon, which completes one revolution around Neptune every 23 hours, NASA said.
