Neptune is one of the distant and not very studied planets of our solar system. If we consider the position of the celestial bodies from the Sun, Neptune will be the eighth - penultimate planet. For a long time, before the launch of the Voyager 2, it was difficult to study this space object not only because of its remoteness, but also because of the presence of a ring system that partially changed its shape. From the article it will become clear which planet has the satellites Triton and Nereid, what are their features and how they were discovered.
Astronomers divide the numerous moons of Neptune into internal and external. Internal satellites are small celestial bodies held by gravity near the planet and passing along a circular orbital path. The outer ones are located far from Neptune, have a fairly large mass and pass through unusual orbits.
Discovery of Neptune's satellites
To date, there are 14 known Neptune satellites orbiting in its orbit. Most of them were discovered recently, when the path of the Voyager 2 spacecraft passed close to a distant planet, which made it possible to take detailed pictures. Before that, only two satellites were known - Nereid and the first Triton found first.
The honor of the discovery of Neptune's largest satellite, Triton, belongs to the English astronomer William Lassel. This happened in 1846, just 17 days after two famous German astronomers announced the discovery of the planet Neptune itself.
For a long time, Triton did not have its own name - it was designated on astronomical maps as a satellite of Neptune. And only after another satellite was discovered - Nereid, received its official name and Triton.
The discovery of Nereida occurred in 1949 - more than a hundred years after the planet itself and its first satellite were found in the sky. The American astronomer Gerald Kuiper made this discovery. It is surprising that he made this discovery using a ground-based telescope.
Mysterious Triton
The visit of Voyager 2 to Neptune confirmed the theoretical calculations of astronomers that Triton is the largest satellite of this distant planet. Its diameter is 2706 km, which is not much less than the diameter of the moon. And the mass of Triton is only 3.5 times less than the satellite of our planet.
Its surface is completely covered with ice, consisting of frozen gases (methane and nitrogen), so the light of the Sun reflects well from it and can be seen through a telescope.
Triton rotates in an unusual orbit: it moves in the opposite direction to the motion of its planet, that is, it moves clockwise, and not against it. This movement is called retrograde. Another unusual fact is that the orbit of Triton is an almost regular circle and is rather strongly inclined to the equator.
Based on the unusual characteristics of Triton, astronomers assume that this is not exactly a satellite of the planet. Rather, he was an independent celestial body that was captured by the superior gravity of Neptune.
The distant companion of Nereid
The diameter of this celestial body is approximately 340 km. He is considered the third largest moon of Neptune, after Triton and Proteus. Its one revolution around the planet lasts almost an earthly year - 360 days. Perhaps this is due to the fact that its orbit is very elongated: it either approaches Neptune at a distance of 1.4 million kilometers, then it moves away at 9.66 million kilometers. Nereid, unlike Triton, has an irregular shape.
For the planetary satellites already studied in the solar system, such an unusual elongated orbit is not typical. This led astronomers to the idea that Nereid used to be an asteroid, possibly from the Kuiper belt, which fell into the field of gravity of Neptune and remained in its orbit.
So far, scientists have no detailed photos of the satellite of Neptune Nereida. In 1989, the Voyager 2 apparatus passed Neptune, which took and sent to Earth many pictures of the planet itself and its satellites. However, at this time, Nereida was at a very great distance and the apparatus was unable to take detailed pictures of its surface. Therefore, this celestial body is still the most poorly studied of the many moons of Neptune.
Interesting facts known to astronomers
Scientists estimate that the mass of Triton is more than 90% of the total mass of all the satellites of Neptune. All other numerous satellites of this planet, including Nereid, are substantially smaller.
The time of year on Triton lasts approximately forty earthly years.
Thanks to many years of observations, astronomers are sure that the structure of Triton resembles a planetary one: it has a stone core with a diameter of about 2000 kilometers, which is covered with a mixture of ice and rock fragments.
This satellite is considered one of the coldest cosmic bodies in our galaxy - even nitrogen freezes at its surface at an average temperature of -235 degrees Celsius. At the same time, active nitrogen geysers often arise on its surface, the height of which can reach ten meters. Thanks to this phenomenon, Triton has its own atmosphere, consisting of methane and nitrogen. As recorded by Voyager 2, there are even clusters of clouds consisting of these gases above the satellite’s surface.
For a long time, astronomers considered the satellite Nereid to be the most distant, but, in the light of recent discoveries, this opinion has changed.
So far, most of the data is known to scientists through a visit to the Voyager 2 device. However, there is a project to launch the next research vessel, planned for 2030.