Venus is the second
planet from the
Sun, orbiting it every 224.7 Earth days. The planet is named after
Venus, the
Roman goddess of love and beauty. After the
Moon, it is the brightest natural object in the night sky, reaching an
apparent magnitude of −4.6, bright enough to cast shadows. Because Venus is an
inferior planet from
Earth, it never appears to venture far from the Sun: its
elongation reaches a maximum of 47.8°. Venus reaches its maximum brightness shortly before sunrise or shortly after sunset, for which reason it has been known as the Morning Star or Evening Star.
Venus is classified as a
terrestrial planet and it is sometimes called Earth's "sister planet" due to the similar size, gravity, and bulk composition. Venus is covered with an opaque layer of highly reflective
clouds of
sulfuric acid, preventing its surface from being seen from space in
visible light. Venus has the densest
atmosphere of all the terrestrial planets in our
solar system, consisting mostly of
carbon dioxide. Venus has no
carbon cycle to lock carbon back into rocks and surface features, nor does it seem to have any organic life to absorb it in biomass. A younger Venus is believed to have possessed Earth-like oceans,
[11] but these evaporated as the temperature rose. Venus's surface is a dusty dry desertscape with many slab-like rocks, periodically refreshed by volcanism. The water has most likely
dissociated, and, because of the lack of a planetary magnetic field, the hydrogen has been swept into interplanetary space by the
solar wind.
[12] The
atmospheric pressure at the planet's surface is 92 times that of the Earth.
The Venusian surface was a subject of speculation until some of its secrets were revealed by
planetary science in the twentieth century. It was finally mapped in detail by
Project Magellan in 1990–91. The ground shows evidence of extensive
volcanism, and the
sulfur in the atmosphere may indicate that there have been some recent eruptions.
[13][14] However, the absence of evidence of
lava flow accompanying any of the visible
caldera remains an enigma. The planet has few
impact craters, demonstrating that the surface is relatively young, approximately 300–600 million years old.
[15][16] There is no evidence for
plate tectonics, possibly because its crust is too strong to
subduct without water to make it less
viscous. Instead, Venus may lose its internal heat in periodic massive resurfacing events.
[15]
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