This encounter facilitated Triton's capture to an inclined retrograde orbit around Neptune, an event that catastrophically altered the Neptune satellite system. In the image, Neptune is orbited by several primordial satellites that may have existed prior to the binary-planet encounter. These satellites would have been collisionally destroyed in the aftermath of Triton's capture to a large eccentric orbit.
By Tim Stephens Neptune's large moon Triton may have abandoned an earlier partner to arrive in its unusual orbit around Neptune. Triton is unique among all the large moons in the solar system because it orbits Neptune in a direction opposite to the planet's rotation a "retrograde" orbit.
It is unlikely to have formed in this configuration and was probably captured from elsewhere. In the May 11 issue of the journal Nature, planetary scientists Craig Agnor of UCSC and Douglas Hamilton of the University of Maryland describe a new model for the capture of planetary satellites involving a three-body gravitational encounter between a binary and a planet.
According to this scenario, Triton was originally a member of a binary pair of objects orbiting the Sun. Gravitational interactions during a close approach to Neptune then pulled Triton away from its binary companion to become a satellite of Neptune. In addition, this mechanism introduces a new pathway for the capture of satellites by planets that may be relevant to other objects in the solar system," said Agnor, an assistant researcher in UCSC's Center for the Origin, Dynamics, and Evolution of Planets.
With properties similar to the planet Pluto and about 40 percent more massive, Triton has an inclined, circular orbit that lies between a group of small inner moons with prograde orbits and an outer group of small satellites with both prograde and retrograde orbits.
There are other retrograde moons in the solar system, including the small outer moons of Jupiter and Saturn, but all are tiny compared to Triton less than a few thousandths of its mass and have much larger and more eccentric orbits about their parent planets. Triton may have come from a binary very similar to Pluto and its moon Charon, Agnor said.
Charon is relatively massive, about one-eighth the mass of Pluto, he explained. Picture of the Day Image Galleries. Watch : Mining the Moon for rocket fuel. Queen guitarist Brian May and David Eicher launch new astronomy book. Last chance to join our Costa Rica Star Party! Learn about the Moon in a great new book New book chronicles the space program. Dave's Universe Year of Pluto. Groups Why Join? Astronomy Day. The Complete Star Atlas.
Bringing the universe to your door. Figuring out how this scenario could result in such a circular and well-behaved orbit requires some mathematical gymnastics. The model that works best is that Triton was once a giant double-body roaming the outer solar system.
Passing Neptune, Triton lost enough energy to be captured, while its companion gained energy and was expelled. Odd indeed.
Here's what they would have done. Four crazy stars astronomers think might really exist. Uranus and Neptune's differences might boil down to collisions. A weird, orbital dance keeps these moons of Neptune safely on track. How Voyager opened the door to the ice giants. Neptune peaks in Aquarius. Cosmos: Origin and Fate of the Universe.
Astronomy's Moon Globe. Galaxies by David Eicher. Astronomy Puzzles. Jon Lomberg Milky Way Posters. Astronomy for Kids. Want to leave a comment? Only registered members of Astronomy. Registration is FREE and only takes a couple minutes.
Login or Register now. It shares many similarities with Pluto, the best known world of the Kuiper Belt. But because of its unusual orbital inclination both polar regions take turns facing the Sun. Triton has a diameter of 1, miles 2, kilometers. Spacecraft images show the moon has a sparsely cratered surface with smooth volcanic plains, mounds and round pits formed by icy lava flows. Triton consists of a crust of frozen nitrogen over an icy mantle believed to cover a core of rock and metal.
Triton has a density about twice that of water. This is a higher density than that measured for almost any other satellite of an outer planet. Europa and Io have higher densities. This implies that Triton contains more rock in its interior than the icy satellites of Saturn and Uranus.
Triton's thin atmosphere is composed mainly of nitrogen with small amounts of methane. This atmosphere most likely originates from Triton's volcanic activity, which is driven by seasonal heating by the Sun. Triton, Io and Venus are the only bodies in the solar system besides Earth that are known to be volcanically active at the present time. Triton is one of the coolest objects in our solar system.
It is so cold that most of Triton's nitrogen is condensed as frost, giving its surface an icy sheen that reflects 70 percent of the sunlight that hits it. During its flyby, Voyager 2 also found Triton has active geysers, making it one of the few geologically active moons in our solar system.
0コメント