An announcement from NASA:

WASHINGTON — NASA’s Hubble Space Telescope has discovered 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 across, making it the smallest known moon in the Neptunian system. 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. 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.

Mark Showalter of the SETI Institute in Mountain View, Calif., found the moon 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. “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.

On a whim, Showalter looked far beyond the ring segments and noticed the white dot about 65,400 miles from Neptune, located between the orbits of the Neptunian moons Larissa and Proteus. The dot is S/2004 N 1. Showalter plotted a circular orbit for the moon, which completes one revolution around Neptune every 23 hours.

The Hubble Space Telescope is a cooperative project between NASA and the European Space Agency. NASA’s Goddard Space Flight Center in Greenbelt, Md., manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Md., conducts Hubble science operations. STScI is operated by the Association of Universities for Research in Astronomy Inc., in Washington.

For images, video, and more information Neptune’s new moon, visit: http://hubblesite.org/news/2013/30

For more information about the Hubble Space Telescope, visit: http://www.nasa.gov/hubble

Hubble Finds New Neptune Moon

July 15, 2013: In the summer of 1989, a robotic emissary from Earth visited the farthest major planet from the Sun, Neptune. Like any good tourist, NASA’s Voyager 2 spacecraft snapped a lot of pictures during the brief flyby. The prolific probe discovered several moons orbiting close to the blue-green planet. But one moon, no bigger than a metropolitan city and nearly coal-black, escaped detection because it was too faint to be seen. Until now.

While analyzing Neptune photos taken by the Hubble Space Telescope, astronomer Mark Showalter of the SETI Institute noticed an extra white dot about 65,400 miles from Neptune, located between the orbits of the moons Larissa and Proteus. Hubble’s extraordinary sensitivity and sharpness caught an object that is roughly one hundred million times fainter than the faintest star that can be seen with the naked eye. Thankfully, Showalter also had 150 archival Neptune photographs taken by Hubble from 2004 to 2009. The same white dot appeared over and over again. This allowed him to plot a circular orbit for the moon, designated S/2004 N 1, which completes one revolution around Neptune every 23 hours. His discovery raises the number of known moons orbiting Neptune to 14.