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The known icy moons in this range are all ellipsoidal (except Proteus), but trans-Neptunian objects up to 450–500 km radius may be quite porous. [10] For simplicity and comparative purposes, the values are manually calculated assuming that the bodies are all spheres. The size of solid bodies does not include an object's atmosphere.
The Moon is Earth's only natural satellite.It orbits at an average distance of 384,400 km (238,900 mi), about 30 times the diameter of Earth. Tidal forces between Earth and the Moon have synchronized the Moon's orbital period (lunar month) with its rotation period at 29.5 Earth days, causing the same side of the Moon to always face Earth.
Irregular moons are probably minor planets that have been captured from surrounding space. Most irregular moons are less than 10 kilometres (6.2 mi) in diameter. The earliest published discovery of a moon other than Earth's was by Galileo Galilei, who discovered the four Galilean moons orbiting Jupiter in 1610. Over the following three ...
Surveyor 7 observes levitating dust, a phenomenon named Lunar horizon glow can be seen The thin lunar atmosphere is visible on the Moon's surface at sunrise and sunset with the lunar horizon glow [1] and lunar twilight rays, like Earth's crepuscular rays. This Apollo 17 sketch depicts the glow and rays [2] among the general zodiacal light [3] [4].
To support an Earth-like atmosphere for about 4.6 billion years (Earth's current age), a moon with a Mars-like density is estimated to need at least 7% of Earth's mass. [20] One way to decrease loss from sputtering is for the moon to have a strong magnetic field of its own that can deflect stellar wind and radiation belts.
Aegaeon is the smallest known moon of Saturn outside of the rings and has an extremely elongated shape, measuring 1.4 km × 0.5 km × 0.4 km (0.87 mi × 0.31 mi × 0.25 mi) in size. [9] Measurements of its mass show that Aegaeon has a very low density, likely due to a highly porous and icy interior structure. [ 5 ]
The Moon's density is substantially less than that of Earth, due to its lack of a large iron core. [3] On Earth , physical and chemical differentiation processes led to a crustal density of approximately 2700 kg/m 3 compared to the 3400 kg/m 3 density of the compositionally different mantle just below, and the average density of the planet as a ...
The distinction between a satellite and a classical planet was not recognized until after the heliocentric model of the Solar System was established. When in 1610 Galileo discovered the first satellites of another planet (the four Galilean moons of Jupiter), he referred to them as "four planets flying around the star of Jupiter at unequal intervals and periods with wonderful swiftness."