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Mercury's surface is similar in appearance to that of the Moon, showing extensive mare-like plains and heavy cratering, indicating that it has been geologically inactive for billions of years. It is more heterogeneous than the surface of Mars or the Moon, both of which contain significant stretches of similar geology, such as maria and plateaus ...
A "moon" was detected moving away from Mercury in 1974, and was eventually identified as a background star, 31 Crateris. 31 Crateris is a spectroscopic binary with a period of 2.9 days, and this may have been the source of the ultraviolet radiation detected in 1974.
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.
The geology of Mercury is the scientific study of the surface, crust, and interior of the planet Mercury. It emphasizes the composition, structure, history, and physical processes that shape the planet. It is analogous to the field of terrestrial geology. In planetary science, the term geology is used in its broadest sense to mean the study of ...
Of the inner planets, Mercury and Venus have no natural satellites; Earth has one large natural satellite, known as the Moon; and Mars has two tiny natural satellites, Phobos and Deimos. The giant planets have extensive systems of natural satellites, including half a dozen comparable in size to Earth's Moon: the four Galilean moons , Saturn's ...
Planetary phase. The evolution of the apparent diameter and phases of Venus. A planetary phase is a certain portion of a planet 's area that reflects sunlight as viewed from a given vantage point, as well as the period of time during which it occurs. The phase is determined by the phase angle, which is the angle between the planet, the Sun and ...
Atmosphere of Mercury. Mercury's surface, with the atmosphere too thin to be visible. Mercury, being the closest to the Sun, with a weak magnetic field and the smallest mass of the recognized terrestrial planets, has a very tenuous and highly variable atmosphere (surface-bound exosphere) containing hydrogen, helium, oxygen, sodium, calcium ...
A lunar eclipse as viewed from Mercury, captured from the MESSENGER spacecraft. The Moon can be seen falling into the shadow of Earth. The Earth and the Moon also will be very bright, their apparent magnitudes being about −5 [3] and −1.2, respectively. The maximum apparent distance between the Earth and the Moon is about 15′.