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The existence of a lunar core is still debated; however, if it does have a core it would have formed synchronously with the Earth's own core at 45 million years post-start of the Solar System based on hafnium-tungsten evidence [36] and the giant impact hypothesis. Such a core may have hosted a geomagnetic dynamo early on in its history. [28]
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]
Earth has one Moon, the largest moon of any rocky planet in the Solar System and the largest body typically described as a moon that orbits anything in hydrostatic equilibrium in relation to the primary object by mass and diameter other than Charon and Pluto, the latter two being dwarf planets revolving around each other.
[f] Six planets, seven dwarf planets, and other bodies have orbiting natural satellites, which are commonly called 'moons'. The Solar System is constantly flooded by the Sun's charged particles, the solar wind, forming the heliosphere. Around 75–90 astronomical units from the Sun, [g] the solar wind is halted, resulting in the heliopause.
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.
In 2001, S. Labrosse and others, assuming that there were no radioactive elements in the core, gave an estimate of 1±0.5 billion years for the age of the inner core — considerably less than the estimated age of the Earth and of its liquid core (about 4.5 billion years) [58] In 2003, the same group concluded that, if the core contained a ...
Earth may have had a ring made up of a broken asteroid over 400 million years ago, a study finds. The Saturn-like feature could explain a climate shift at the time.
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 ...