[meteorite-list] Archival Hubble Images Reveal Neptune's "Lost" Inner Moon, Naiad

[Ron Baalke]

http://www.seti.org/seti-institute/press-release/archival-hubble-images-reveal-neptunes-lost-inner-moon

Archival Hubble Images Reveal Neptune's "Lost" Inner Moon, Naiad 
SETI Institute
October 8, 2013

Neptune's tiny, innermost moon, Naiad, has now been seen for the first 
time since it was discovered by Voyager's cameras in 1989. Dr. Mark Showalter, 
a senior research scientist at the SETI Institute in Mountain View, California, 
announced the result today in Denver, Colorado, at the annual meeting 
of the Division for Planetary Sciences of the American Astronomical Society. 
He and collaborators Dr. Jack Lissauer of the NASA Ames Research Center, 
Dr. Imke de Pater of UC Berkeley, and Robert French of the SETI Institute, 
also released a dramatic new image of Neptune's puzzling rings and ring-arcs, 
which were first imaged by Voyager.

"Naiad has been an elusive target ever since Voyager left the Neptune 
system," said Dr. Showalter. From Earth, Neptune is 2 million times brighter 
than Naiad, andthetwo are separated by only one arcsecond. "This is equivalent 
to the width of a human hair from 50 feet away," noted collaborator Lissauer. 
The team of astronomers needed to develop new techniques to suppress Neptune's 
glare. Naiad was finally revealed, moving across a sequence of eight images 
taken during December 2004.

Strangely, Naiad appears to have veered significantly off course. The 
astronomers are puzzled by the fact that Naiad is now far ahead of its 
predicted orbital position. They wonder whether gravitational interactions 
with one of Neptune's other moons may have caused it to speed up, although 
the details remain mysterious. Further observations will be needed in 
order to understand Naiad's motion.

In addition to its moons, Neptune hosts a family faint rings and ring-arcs. 
The arcs have been changing slowly in the years since their discovery. 
Whereas Voyager saw a set of four closely-spaced arcs, the leading two 
arcs have been fading away, and are completely absent from the newest 
images. The trailing arcs, however, are essentially unchanged. This system 
of arcs is probably confined by the gravitational effects of the nearby 
moon Galatea, but the reason for the long-term changes is unknown. Dr. 
de Pater has also been following the ongoing evolution of the arcs from 
the 10-meter W. M. Keck telescope in Hawaii.

Showalter and his collaborators had previously announced the discovery 
of a tiny moon of Neptune in July. That moon, which is no more than 20 
km (12 miles) across, goes by the provisional designation "S/2004 N 1". 
The new results reported today are based on further analysis of the same 
images, which were all obtained by Hubble between 2004 and 2009. Although 
100-km Naiad is much larger than the moon announced in July, it orbits 
much closer to Neptune and so has proven to be much harder to detect.

"It is always exciting to find new results in old data," Showalter remarked. 
"We keep discovering new ways to push the limit of what information can 
be gleaned from Hubble's vast collection of planetary images."

Support for this work was provided by NASA through grant number from the 
SPACE TELESCOPE SCIENCE INSTITUTE, which is operated by the Association 
of Universities for Research in Astronomy, Inc., under NASA contract 
NAS5-26555.