Astronomy

Neptune’s Lost Moon, Naiad



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"Neptune's Lost Moon, Naiad"
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It's hard to imagine that something as large as a moon could be lost, but that's exactly what happened to Naiad, Neptune's closest moon. The 62 mile-wide moon went missing in 1989, shortly after it was discovered by the cameras of NASA's Voyager 2 spacecraft. In spite of attempts to locate Naiad via ground-based telescopes, along with a 2004 pursuit utilizing the Hubble Space Telescope, no definitive evidence of the moon was revealed.

Naiad has been obscured by Neptune – which is 35 million miles away from earth – for 24 years, and has finally been tracked down by Hubble. Viewed from Earth, Neptune is 2 million times brighter than Naiad, and they're separated by an arcsecond, which equates to the width of a human hair from 50 feet away. Astronomers needed to search for a method of subduing Neptune's glare so that Naiad could be seen.

Scientists at California's SETI (Search for Extraterrestrial Intelligence) Institute speculated that they could detect Naiad by employing a method that had recently assisted them in discovering a much smaller, completely new Neptunian moon, temporarily called S/2004 N 1. Overlaying eight Hubble photos from the 2004 Naiad quest in order to replicate a much longer exposure, they revealed elements that had previously been too subtle to see – including Naiad itself.

The image-layering technique disclosed that Naiad's whereabouts had been concealed for so long partially because its orbit differed dramatically from the orbit predicted by the Voyager data. The moon has swerved drastically off course and is now considerably beyond its expected orbital location. It's speculated that Neptune's 12 other moons are pushing and pulling Naiad, giving it an unpredictable, wobbly orbit. Over periods of approximately a decade each cycle, Naiad speeds up and slows down without a discernible pattern. These wobbles might be the first signs that Neptune's whole moon system is volatile, although it may be tens of billions of years before any disastrous collisions occur.

When Naiad was first discovered, it was initially identified as S/1989 N 6. It acquired its official name on September 16, 1991. Traditionally, Neptune's moons are named after mythological figures relating to the Roman god Neptune, lord of the sea, or his Greek counterpart, Poseidon. The planet's irregular satellites are named after the Nereids, daughters of Nereus and Doris, and Neptune's attendants. Naiad was named after a Greek mythological nymph who ruled over any type of fresh water – brooks, wells, streams and springs.

Naiad is Neptune's closest moon, orbiting 14,400 miles above the cloud tops every seven hours and six minutes. The satellite's orbit is brief because of its proximity to the blue planet. A tiny moon, Naiad is approximately one-sixtieth the size of Earth's moon, and its mass is so miniscule that it is only 0.00001 percent of our moon's mass. It revolves around Neptune in the same direction that the planet rotates, staying near to Neptune's equatorial plane. Because it has an orbital decay, which is the prolonged reduction in the altitude of its orbit, Naiad may eventually collide with Neptune, or be torn apart and transformed into part of its planetary rings. Astronomers reason that Naiad is composed of fragments from Neptune's original moons, some of which were demolished when Neptune's gravity caught Triton, its largest moon, as a satellite. They don't believe Naiad has undergone any geological changes since its formation.

In the far reaches of our galaxy, Naiad remained well secluded until it was revealed by a recent scientific breakthrough. The moon that has been playing hide-and-seek with astronomers for more than two decades has finally lost the game.

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More about this author: Merryl Lentz

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ARTICLE SOURCES AND CITATIONS
  • InfoBoxCallToAction ActionArrowhttp://www.space.com/17693-voyager-2.html
  • InfoBoxCallToAction ActionArrowhttp://hubblesite.org/the_telescope/
  • InfoBoxCallToAction ActionArrowhttp://www.seti.org/