Word: nereid
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Though Voyager is still about 22 million miles from Neptune, it has already made several discoveries. It has found a new moon to add to the known duo, % Triton and Nereid. Labeled 1989-N1, the object is between 125 and 400 miles across and has a surprisingly ordinary orbit. Like most moons, 1989-N1 orbits nearly over its planet's equator and in the same direction as the planet's rotation, implying that it formed with or soon after Neptune...
...about the size of earth's moon, orbits in the opposite direction. That has led astronomers to guess that Triton might be a large asteroid that was captured by Neptune's gravity. Such an intrusion should have disrupted the paths of any existing moons. This would explain tiny Nereid's highly elongated and tilted orbit. But 1989-N1 is just "sitting there," says Voyager project scientist Torrence Johnson, of the Jet Propulsion Laboratory. Johnson expects that the probe will discover more moons, shedding light on Triton's origins. "All of the outer planets have lots of junk around them...
Neptune's Tides. McCord's calculations seem to support what other scientists have suspected. Long ago, as it sank from a higher orbit, Triton passed close to Nereid. The smaller moon, buffeted by Triton's more powerful gravity, may have been hurled into the elliptical orbit it now follows...
Like many scientists before him, Caltech Graduate Student Thomas McCord was searching for other answers when he made his unexpected discovery. Curious about the odd behavior of the planet Neptune's two moons, Triton and Nereid, he set out to make a mathematical analysis of their unusual orbits. Last week in the Astronomical Journal, he reported that his two-year, computer-aided investigation had not only accounted for the current state of the Neptunian satellites but had also given him a startling glimpse into the future: Triton, largest of the two moons, is doomed to smash into Neptune...
...distance of 220,000 miles, about the same distance as the moon is from the earth. But unlike the earth's moon and most other solarsystem satellites, Triton moves in a retrograde direction: it circles the "wrong" way-clockwise-around Neptune which spins counterclockwise on its axis. Nereid, only about 200 miles in diameter, revolves in the direction of Neptune's spin, but its orbital path is highly irregular, swinging as far as 6,000,000 miles into space and as close as 900,000 miles from Neptune's surface...