Monday, July 15, 2013 1:26pm -0400

A New Moon Discovered Around Neptune

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Orbit of Neptune's New Moon Orbit of Neptune's New Moon NASA, ESA, and A. Feild (STScI)

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.


 

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."Neptunes Moon 2

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.

Neptune's largest moon, Triton, which is nearly the size of Earth's moon, may be a captured icy dwarf planet from the Kuiper Belt at the outer rim of our solar system. This capture would have gravitationally torn up any original satellite system Neptune possessed. Many of the moons now seen orbiting the planet probably formed after Triton settled into its unusual retrograde orbit about Neptune.

The outer moon Triton was discovered in 1846 — the same year the planet itself was discovered. Triton's orbit is retrograde, suggesting it is a captured Kuiper Belt object and therefore a distant cousin of Pluto. The inner moons may have formed after Triton's capture several billion years ago.

Credit: NASA/Hubble

Read 3924 times Last modified on Monday, July 15, 2013 1:54pm -0400
Laurel Nendza

Laurel Nendza is the owner and creator of Stellar Eyes.