SETI Institute Scientist Mark Showalter Finds New Moon Around Neptune

Mountain View — 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."

When imaged by the Hubble Telescope, Neptune's moons and arcs smear out because of their rapid orbital motion. Showalter re-processed the images to compensate for this smear, and discovered the new moon as an extra white dot that had not been visible before. The moon is too faint to be seen in individual images, but can be seen clearly when sets of 8-10 images are added together. In all, Showalter processed 150 images taken by Hubble between 2004 and 2009. He then 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.

Collaborators: Imke de Pater (UC Berkeley), Jack Lissauer (NASA Ames) and Rob French (SETI Institute).

Related links:

Mark Showalter's blog on Cosmic Diaries:

For images and more information about Neptune's new moon, visit:

For more information about the Hubble Space Telescope, visit:

About SETI Institute

The mission of the SETI Institute is to explore, understand, and explain the origin and nature of life in the universe and to apply the knowledge gained to inspire and guide present and future generations. Our research, education and outreach programs explore the wonder of the universe and celebrate the excitement of exploration and the joy of discovery for all humankind.