The Moons of Neptune Trivia Quiz

Answer: Triton

Triton did not receive its name until Camille Flammarion proposed it in his book "Astronomie Populaire" in 1880. Even then, it was still called 'Neptune's Moon', or 'the satellite of Neptune' until Triton came into popular use in the 1930s. Triton, of course, is the son of Poseidon of Greek mythology, and Poseidon is the Greek equivalent of the Roman god Neptune.

Astronomers believe that Triton was captured into Neptune's orbit, largely due to the fact that it has a retrograde orbit, meaning that it goes around Neptune in the opposite direction of the planet's rotation.

Triton is the seventh largest moon in the solar system (sixteenth largest overall), and it has more mass than every moon that is smaller than itself, combined. With numbers, Triton is 2,700 km in diameter, and orbits at a distance of 354,759 km (from the centre of Neptune).

Answer: Gerard Peter Kuiper

Gerard Kuiper discovered Nereid through photographic plates from the 82-inch telescope at the McDonald Observatory in Texas, USA on the 1st of May, 1949. Following the pattern established by the names Neptune and Triton, Kuiper suggested Nereid as the name of this new moon, after the sea-nymphs who attended Poseidon.

Nereid is an irregular moon with an eccentric orbit, but it does orbit in a prograde direction. It is the next moon out from Triton, but it orbits MUCH further out. Where Triton's semi-major axis is at 354,759 km, Nereid's varies between (approximately) 900,000 km and 6,000,000 km (the largest such variance of any observed moon).

Answer: True

On May 24th, 1981, Harold J. Reitsema, William B. Hubbard, Larry A. Lebofsky and David J. Tholen were watching the approach of a star towards Neptune. They were looking for the telltale sign of the presence of rings around Neptune - a slight reduction in luminosity just as the star came closest. What they ended up seeing was a short occlusion - a shadow - that could only be the presence of a moon.

That was the only indication of the presence of a third moon (Larissa) around Neptune prior to 1989 when a deep space probe flew past the planet and verified its existence.

Larissa was a nymph lover of Poseidon in Greek mythology.

Answer: Voyager 2

Voyager 2 was launched, as mentioned, on August 20th, 1977, and its primary mission was completed after visiting our solar system's four gas giants - Jupiter in 1979, Saturn in 1981, Uranus in 1986, and Neptune in 1989. Its extended mission was to continue on to visit the Kuiper Belt, the edge of our Heliosphere, and beyond. At the time of my writing this quiz (February, 2015), data transmissions were still being received from Voyager 2.

When Voyager 2 visited Neptune, astronomers only knew of two Neptunian moons for sure, with a possible third. The flyby increased the number of known moons around Saturn to eight.

Answer: Naiad

Naiad is orbiting about 23,500 km above the surface of Neptune, and is in a decaying orbit, meaning that one day, far into the future, the moon could fall into Neptune's atmosphere, or perhaps break up and form a planetary ring.

Naiad is about 58 km in diameter, and orbits Neptune every seven hours and six minutes. It was the last of the inner moons to be discovered during Voyager 2's flyby.

Answer: Proteus

Proteus is about 420 km in diameter and was discovered by Voyager 2 approximately two months before flying by Neptune. While it is the second largest moon of Neptune, Triton by itself has over 99% of all the mass in orbit around the planet.

Proteus orbits at a semi-major axis of 117,646 km, and lies between Triton and the fourteenth Neptunian moon (discovered in 2013 in Hubble telescope photos), designated S/2004 N 1.

Between Naiad and S/2004 N 1 are Thalassa, Despina, Galatea and Larissa. With the exception of S/2004 N 1, each of the inner moons gets progressively larger the further from the planet. Their diameters are (approximately): Naiad - 58 km; Thalassa - 82 km; Despina - 150 km; Galatea - 176 km; Larissa - 194 km; S/2004 N 1 - 18 km; and Proteus - 420 km.

Answer: True

Because evidence indicates that Triton was captured by Neptune (probably from the Kuiper Belt), it is believed that it likely wreaked havoc on any natural satellites that were already in orbit around the planet. All of the small inner moons between Neptune and Triton seem to have been re-accreted from the rubble disc that would have been created by that event.

Answer: False

Triton and Nereid and all five of the other outer moons are irregular moons. Triton, as mentioned earlier, has a retrograde orbit, while Nereid has a prograde orbit. Of the remaining five, three are in a retrograde orbit, while two are prograde.

Four of these discovered by a team of astronomers led by Matthew Holman and JJ Kavelaars in 2002. They used an innovative technique to discover these outer moons, combining photos from two different telescopes (in Hawaii and Chile), and superimposing multiple frames to enhance the visibility of faint objects.

The observations were done in mid-August, but only three new moons were initially discovered at that time - eventually taking the names Halimede, Sao and Laomedeia. The fourth (Neso), was not discovered in the photographs until 2003.

The fifth moon (Psamathe), was discovered in 2003 by Scott S. Sheppard and David C. Jewitt, using the Subaru telescope at the National Astronomical Observatory of Japan.

Answer: Halimede

Astronomers give it a 41% probability that Halimede is a fragment of Nereid, based on striking similarities in colour and surface appearance. At a diameter of only 62 kilometres, Halimede is not that big, and barely beats out Neso's 60 kilometre diameter. Even so, it is definitely bigger than Sao's 44 kilometres, Laomedeia's 42 kilometres, and Psamathe's 40 kilometres.

Answer: It is the most distant known moon of any planet.

Neso orbits Neptune at a range of more than 49 Gm (49,000,000 km). And it has an elliptical orbit, so when it is at its apocenter, it is more than 72 Gm from Neptune! It is a small moon, only measuring approximately 60 metres in diameter, and takes more than 26 years to orbit the planet (also a record).

The neighbouring moon Psamathe has a similar orbit, although not *quite* as far out (only 48 Gm). It is believed that the two moons were the same entity at some point in history.