Triton, Neptune’s largest moon, was discovered on October 10, 1846. William Lassell, an English amateur astronomer, found the satellite just seventeen days after Neptune itself had been discovered.
Until Voyager 2 streaked past the intriguing moon in August of 1989, Triton remained little more than a tiny point of light to earthbound astronomers. Scientists knew from spectroscopic studies that Triton possesses an atmosphere and that it orbits about 220,000 miles from the center of Neptune, but they remained uncertain of its size and many other physical properties.
Triton’s most unusual characteristic, at least from Earth-based observations, is its orbit, which is “backwards”. Unlike any other major satellite in the solar system, Triton orbits in the direction opposite to its parent planet’s rotation. Scientists theorize that Triton formed separately from Neptune and was captured later when it drifted too close to the giant blue planet.
The television cameras of Voyager 2 revealed an amazing frozen world of mountains, fault lines and ice volcanos. Triton is one of only three worlds in the solar system, along with Earth and Jupiter’s moon Io, known to have active volcanos.
Several Voyager photographs showed dark irregular blemishes on Triton’s surface. The patches may be slushy ponds of frozen nitrogen spewed from volcanic vents. Although the surface is so cold that nitrogen freezes solid, tidal forces below the surface could turn the nitrogen ice into slush. As pressure builds, the slush forces its way to the surface in an explosive eruption. Voyager’s instruments detected thin clouds above the dark spots, further evidence of volcanic eruptions.
Neptune’s Extraordinary Moon Triton