NASA's Hubble Space Telescope has discovered a new moon orbiting the distant blue-green planet Neptune. This brings the number of known satellites circling the giant planet to 14.
The body is estimated to be no more than 12 miles across, making it
the smallest known moon in the Neptunian system. It's so small that it
escaped detection by NASA's Voyager 2 spacecraft, which flew by Neptune
in 1989 and surveyed the planet's system of moons and rings.
Mark Showalter of the SETI Institute in Mountain View, Calif.,
discovered the moon on July 1, while studying the faint ring-arcs of
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."
On a whim, Showalter extended his analysis outward to regions well
beyond the ring system, and noticed an extra white dot about 65,400
miles from Neptune, located between the orbits of the moons Larissa and
Proteus.
Showalter next analyzed over 150 archival Neptune photographs taken
by Hubble from 2004 to 2009. The same white dot appeared over and over
again. He then plotted a circular orbit for the moon, which completes
one revolution around Neptune every 23 hours.
The moon, designated S/2004 N 1, is so small and dim that it is
roughly one hundred million times fainter than the faintest star that
can be seen with the naked eye.
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.
CONTACT
Donna Weaver / Ray VillardSpace Telescope Science Institute, Baltimore, Md.
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu
Karen Randall
SETI Institute, Mountain View, Calif.
650-960-4537
krandall@seti.org
