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Satellite 1989N1
Neptune's irregularly - shaped satellite 1989N1 from a range of 870,000 kilometers (540,000 miles) (Click on the image for a larger view)

In addition to the previously known satellites Triton and Nereid, Voyager 2 found six more satellites orbiting Neptune, for a total of eight known satellites. The new objects have not yet been named, a task for the International Astronomical Union (IAU), but were given temporary designations that tell the year of discovery, the planet they are associated with and the order of discovery; for example, 1989N1 was the first satellite of Neptune found that year. The final new body was designated 1989N6.

Nereid was discovered in 1948 through Earth-based telescopes. Little is known about Nereid, which is slightly smaller than 1989N1. Voyager's best photos of Nereid were taken from about 4.7 million kilometers (2.9 million miles), and show that its surface reflects about 14 percent of the sunlight that strikes it, making it somewhat more reflective than Earth's Moon, and more than twice as reflective as 1989N1. Nereid's orbit is the most eccentric in the solar system, ranging from about 1,353,600 km (841,100 miles) to 9,623,700 km (5,980,200 mi).

  • 1989N1, like all six of Neptune's newly discovered small satellites, is one of the darkest objects in the solar system -- "as dark as soot" is not too strong a description. Like Saturn's satellite, Phoebe, it reflects only 6 percent of the sunlight that strikes it. 1989N1 is about 400 kilometers (250 miles) in diameter, larger than Nereid. It wasn't discovered from Earth because it is so close to Neptune that it is lost in the glare of reflected sunlight. It circles Neptune at a distance of about 92,800 kilometers (57,700 miles) above the cloud tops, and completes one orbit in 26 hours, 54 minutes. Scientists say it is about as large as a satellite can be without being pulled into a spherical shape by its own gravity.
  • 1989N2 is only about 48,800 kilometers (30,300 miles) from Neptune, and circles the planet in 13 hours, 18 minutes. Its diameter is about 190 kilometers (120 miles).
  • 1989N3, only 27,700 kilometers (17,200 miles) from Neptune's clouds, orbits every 8 hours. Its diameter is about 150 kilometers (90 miles).
  • 1989N4 lies 37,200 kilometers (23,100 miles) from Neptune. 1989N4, diameter 180 kilometers (110 miles), completes an orbit in 10 hours, 18 minutes.
  • 1989N5 appears to be about 80 kilometers (50 miles) in diameter. It orbits Neptune in 7 hours, 30 minutes about 25,200 kilometers (15,700 miles) above the cloud tops.
  • 1989N6, the last satellite discovered, is about 54 kilometers (33 miles) in diameter and orbits Neptune about 23,200 kilometers (14,400 miles) above the clouds in 7 hours, 6 minutes.

1989N1 and its tiny companions are cratered and irregularly shaped -- they are not round -- and show no signs of any geologic modifications. All circle the planet in the same direction as Neptune rotates, and remain close to Neptune's equatorial plane.

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