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Mercury, the smallest and innermost planet, has no moons, or at least none that can be detected to a diameter of 1.6 km (1.0 mi). [2] For a very short time in 1974, Mercury was thought to have a moon. Venus also has no moons, [3] though reports of a moon around Venus have circulated since the 17th century.
Mars has two relatively small (compared to Earth's) natural moons, Phobos (about 22 kilometres (14 mi) in diameter) and Deimos (about 12 kilometres (7.5 mi) in diameter), which orbit close to the planet. The origin of both moons is unclear, although a popular theory states that they were asteroids captured into Martian orbit. [199]
The sizes and masses of many of the moons of Jupiter and Saturn are fairly well known due to numerous observations and interactions of the Galileo and Cassini orbiters; however, many of the moons with a radius less than ~100 km, such as Jupiter's Himalia, have far less certain masses. [5]
Pluto (bottom left) compared in size to the Earth and the Moon. Pluto's diameter is 2 376.6 ± 3.2 km [5] and its mass is (1.303 ± 0.003) × 10 22 kg, 17.7% that of the Moon (0.22% that of Earth). [125] Its surface area is 1.774 443 × 10 7 km 2, or just slightly bigger than Russia or Antarctica (particularly including the Antarctic sea ice ...
The outer planets Jupiter, Saturn, Uranus and Neptune, compared to the inner planets Earth, Venus, Mars, and Mercury at the bottom right. The four outer planets, called giant planets or Jovian planets, collectively make up 99% of the mass orbiting the Sun. [h] All four giant planets have multiple moons and a ring system, although only Saturn's ...
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.
Saturn's largest moon Titan also has a substantial atmosphere thicker than that of Earth; [118] Neptune's largest moon Triton [119] and the dwarf planet Pluto have more tenuous atmospheres. [120] The larger giant planets are massive enough to keep large amounts of the light gases hydrogen and helium, whereas the smaller planets lose these gases ...
Size of Jupiter compared to Earth and Earth's Moon Jupiter is about ten times larger than Earth ( 11.209 R 🜨 ) and smaller than the Sun ( 0.102 76 R ☉ ). Jupiter's mass is 318 times that of Earth; [ 2 ] 2.5 times that of all the other planets in the Solar System combined.