Neptune's Moon Triton
Neptune's Moon Nereid
Nereid is one of the outermost of Neptune's known moons and is among the largest. Nereid is unique because it has one of the most eccentric orbits of any moon in our solar system. Nereid is so far from Neptune that it requires 360 Earth days to make one orbit.
Nereid's Profile:
Age: Nereid is estimated to be about 4.5 billion years old.
Distance from Jupiter: Nereid orbits Neptune at an average distance of 5,513,400 km (3,425,900 mi), but it also has a very eccentric orbit. The orbit takes Nereid as close as 1,372,000 km (853,000 mi) and as far as 9,655,000 km (5,999,000 mi).
Size: Nereid is Neptune's third largest moon.
Triton is the largest of Neptune's moons. To NASA's knowledge, Triton is the only moon in the solar system thatorbits in a direction opposite to the rotation of its planet. Additionally, its surface is a study of contrasts, with smooth plains appearing to be right next to cratered surfaces.
Neptune, the farthest planet from the sun, has 14 known moons. Almost half of the discoveries took place decades after NASA's Voyager 2 spacecraft swung by the planet and its system, demonstrating just how far telescope technology has progressed.
Image Credit & Copyright: NASA, ESA, and A. Feild
Triton's Profile:
Age: Triton is around 4.5 billion years, about the same age as Neptune
Distance from Jupiter: Triton's orbital distance is about 262,000 miles (422,000 km). Triton takes 5.877 days to orbit, with the same side always facing Neptune. Triton orbits in the opposite direction to Neptune's rotation (called a retrograde rotation).
Size: Triton is 2,700 kilometres (1,700 mi) in diameter, making it the seventh-largest moon and sixteenth-largest object in the Solar System.
Temperature: The temperature at the surface of Triton is only 34.5 K (-235 C, -391 F), as cold as Pluto.
The image was taken by Voyager 2 on Aug. 22, 1989, from a distance of 4 million km (2.5 million miles). Image Credit & Copyright: NASA/JPL
The Discovery of Triton
Triton was found on Oct. 10, 1846, just 17 days after Neptune was discovered. According to NASA, Triton was known simply as "the satellite of Neptune" until 1949, when a second moon (Nereid) was found.
Exploration of Triton
In 1977, NASA sent two Voyager probes on a one-way trip through the outer solar system, taking advantage of a rare planetary alignment that allowed them to move from one location to the next without using a lot of fuel. Voyager 2 flew by Neptune and its system on Aug. 25, 1989.
No spacecraft has gone to Neptune since that time, but telescopes are capturing new data on Triton from the ground. A notable recent find wasdiscovering seasons on the moon, using the European Southern Observatory's Very Large Telescope in Chile.
This color photo of Neptune's large satellite Triton was obtained on Aug. 24 1989 at a range of 530,000 kilometers (330,000 miles). Image Credit & Copyright: NASA/JPL
Discovery
Nereid was discovered on 1 May 1949 by Gerard P. Kuiper with a ground-based telescope. It was the last satellite of Neptune to be discovered before Voyager 2's discoveries four decades later.
Exploration of Neried
The only spacecraft to visit Nereid is Voyager 2, which passed it at a distance of 4,700,000 km (2,900,000 mi)[11] between April 20 and August 19, 1989.[12] Voyager 2 obtained 83 images of the moon with observation accuracies of 70 km (43 mi) to 800 km (500 mi).[12] Prior to Voyager 2's arrival, observations of Nereid had been limited to ground-based observations that could only establish its intrinsic brightness and orbital elements.
This Voyager view of Nereid was obtained on Aug. 24, 1989 at a distance of 4.7 million kilometers (2.9 million miles). Image Credit & Copyright: NASA/JPL