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Although the Moon is Earth's only natural satellite, there are a number of near-Earth objects (NEOs) with orbits that are in resonance with Earth. These have been called "second" moons of Earth or "minimoons". [2] [3] 469219 Kamoʻoalewa, an asteroid discovered on 27 April 2016, is possibly the most stable quasi-satellite of Earth. [4]
Some planetary rings are influenced by shepherd moons, small moons that orbit near the inner or outer edges of a ringlet or within gaps in the rings. The gravity of shepherd moons serves to maintain a sharply defined edge to the ring; material that drifts closer to the shepherd moon's orbit is either deflected back into the body of the ring ...
Among the other dwarf planets, Ceres has no known moons. It is 90 percent certain that Ceres has no moons larger than 1 km in size, assuming that they would have the same albedo as Ceres itself. [6] Eris has one large known moon, Dysnomia. Accurately determining its size is difficult: one indicative estimate of its radius is 350 ± 57.5 km. [7]
Earth may have had a ring made up of a broken asteroid over 400 million years ago, a study finds. ... such as those around Saturn that may have been formed by debris from icy moons, according to NASA.
It is estimated that the A Ring contains 7,000–8,000 propellers larger than 0.8 km in size and millions larger than 0.25 km. [4] In April 2014, NASA scientists reported the possible consolidation of a new moon within the A Ring, implying that Saturn's present moons may have formed in a similar process in the past when Saturn's ring system was ...
Some 4.5 billion years ago, when Earth was only 100 million years old or so, a Mars-sized protoplanet named Theia smashed into our planet, ejecting loads that eventually returned to the Earth’s ...
Secondly, they both have atypically small semi-major axes, with Triton's being over an order of magnitude smaller than those of all other known irregular moons. Thirdly, they both have unusual orbital eccentricities: Nereid has one of the most eccentric orbits of any known irregular satellite, and Triton's orbit is a nearly perfect circle.
There are 293 confirmed moons in our cosmic neighborhood. By studying these worlds, astronomers hope to learn about ancient asteroid collisions, space volcanoes, and the origins of life itself.