Moons of Neptune

Moons of Neptune

What moon in the Solar System has a surface that resembles the rind of a cantaloupe, features geysers that shoot up materials that instantly turn into snow, and was discovered by an English beer baron?

That would be Triton, one of the 13 moons of Neptune. William Lassell discovered the satellite on October 10, 1846, only 17 days after Neptune was discovered by a Berlin observatory. Lassell was an amateur astronomer who funded his star gazing after making a fortune as a brewer. We can only assume he celebrated his discovery with a pint – or two.

Moons of Neptune Triton

It would be more than a century before astronomer Gerard P. Kuiper discovered a second moon of Neptune, Nereid, in 1949. (The Dutch-American astronomer would later have the Kuiper belt named after him.) A third moon, Larissa, was observed by four astronomers in 1981.

Given their vast distance from Earth, the moons of Neptune remained enigmas until Voyager 2 swept past Neptune in 1989. The spacecraft discovered five new satellites - Despina, Galatea, Naiad, Proteus and Thalassa – and made some startling findings about Neptune's known moons.

Voyager 2 discovered ice geysers on Triton's surface that sent plumes, composed of what is believed to be dust, methane and liquid nitrogen, up to 8 km (5 miles) above the moon. This mixture freezes instantly, producing snow that falls back to the surface.

If you're tempted to go build a snowman on Triton, think again. The moon's surface is highly reflective, making the moon extremely cold. Scientists estimate that the surface temperature is about -400 degrees Fahrenheit (-240 degrees Celsius).

Astronomers do not know whether Triton is a natural moon of Neptune or a captured asteroid. The moon's orbit is retrograde, meaning it circles Neptune in a direction opposite of the planet's rotation. This odd orbit, unique among large moons in the Solar System, suggests that the moon originated elsewhere.

Whatever Triton's origin, its orbit around Neptune means that it is ultimately doomed. Triton is slowly being pulled closer to planet; millions of years from now, Neptune's gravity will pull the moon apart and turn it into yet another ring.

Nereid, which is Neptune's third largest moon, has the most eccentric orbit of any satellite in our Solar System. At its closest approach, it orbits 853,000 miles (1,372,000 km) from Neptune and 5,999,000 miles (9,655,000 km) at the farthest.

Scientists believe that this eccentric orbit might result from Nereid being a captured asteroid or Kuiper belt object. Alternately, it might have been an inner moon whose orbit was perturbed when Neptune captured Triton.

There is much we do not know about the 13 moons of Neptune. Voyager 2 was the first - and so far, only - spacecraft to explore the planetary system, and it was not able to enter orbit for prolonged study. Although Earth-based telescopes have been improving, we will have to wait until a future spacecraft orbits the planet to get a really close look at the moons of Neptune.

Links for Moons of Neptune

Neptune's Moons

Neptune: Moons

Voyager Mission

 

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