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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]
The rings are believed to have been present approximately 466 million years ago. [1] [7] [8] The Hirnantian glaciation may be a direct result of the rings shielding light from reaching the Earth, [9] and the rings may have existed for up to 40 million years.
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 ...
Moons are classed into two separate categories according to their orbits: regular moons, which have prograde orbits (they orbit in the direction of their planets' rotation) and lie close to the plane of their equators, and irregular moons, whose orbits can be pro- or retrograde (against the direction of their planets' rotation) and often lie at ...
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 ...
The third form of rock material found on Earth is metamorphic rock, which is created from the transformation of pre-existing rock types through high pressures, high temperatures, or both. The most abundant silicate minerals on the Earth's surface include quartz , the feldspars , amphibole , mica , pyroxene , and olivine . [ 25 ]
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.
Regular moons have several different formation mechanisms. The regular moons of the giant planets are generally believed to have formed from accreting material within circumplanetary discs, growing progressively from smaller moonlets in a manner similar to the formation of planets. Multiple generations of regular satellite systems may have ...