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Mercury Astronomy - Planet Venus Earth

Venus, from Magellan Mass: 4.869 X 1024 kg (0.815 Earths)
Radius (equatorial): 6 052 km
Mean density: 5.25 g cm-3
Distance from Sun: 108 200 000 km
Rotational period: 243.02 days
Orbital period: 224.7 days
Escape velocity: 10.36 km s-1
Apparent magnitude: -4.4
Surface temperature: 482°C
Atmospheric composition: Carbon dioxide (96%), nitrogen (3%), sulfur dioxide, argon, helium etc. (1%)
Number of satellites: none

Characteristics

Historically, Venus is well known as the morning star, or evening star. Named after the Roman goddess of love and beauty its surface is veiled by thick clouds. Beside the Sun and Moon, Venus is the brightest celestial object, shine with steady bright white light. Its physical dimensions are rather similar to that of Earth and is referred to as the Earth's sister planet. Venus rotates very slowly on its axis once every 243 Earth days, longer than the duration it orbits the Sun, every 225 days. It also rotates retrograde, or spin in the opposite direction of its orbit round the Sun. In other words, if one stands on the Venusian surface the Sun would seem to rise in the west and set in the east.

The relationship with the Earth as a twin sister ends when comparing surface features between the two planets. In many respect the Earth would be how Venus looks now if the former volcano activities are increased by hundreds of thousands of times. Geologically speaking, Venus' surface is relatively young that seems to have completely reconstructed 300 to 500 million years ago. Volcano activities, deformation of the crust have shaped the surface. At least 85% of the Venusian surface is covered with volcanic rock with huge lava flows flooded the plains. The flows have also produced channels that extend for hundreds of kilometers. There are at least 1000 volcanoes larger then 20 km and probably over a million more that are over 1 km in diameter. However, there is no direct evidence that these volvanos are still active.

Not surprisingly, its atmosphere is thick with carbon dioxide, probably as a result of its past volcano activities and contains droplets of sulfuric acid. The atmosphere essentially creates a run-away greenhouse effect that allows the Sun's heat in but does not allow it to escape. This results in a temperature that is hotter than Mercury. In addition, the surface pressure is 90 times that of Earth which is why probes that landed on Venus only survived several hours before being crushed by the tremendous pressure. The dense atmosphere also acts as a protective cover against small meteorite impacts as no craters greater than 2 km can be found on the surface.

Recent results from the Magellan spacecraft suggest that Venus’ crust is stronger and thicker than had previously been thought. Venus has no satellites and no intrinsic magnetic field, but the solar wind rushing by Venus creates a pseudo-field around the planet.

Images

The Soviet Union's Venera Missions were the first to touch down on the surface of Venus. However, these probes only survived at most up to two hours (Venera 13). Visual photos taken by telescopes and other flybys only show thick atmospheric cloud which masks the Vanusian surface features. However, the Magellan mission (1990-1994) used radar mapper to reveal for the first time surface features in 3D perspective.

volcano Sapas MonsVolcano Sapas Mons, located in the broad equatorial rise known as Alta Regio. The volcano is about 400 km across and 1.5 km high. Many of the flows appear to have erupted along the flanks of the volcano, rather than from the summit - common on large volcanoes on the Earth.

Credit: Magellan, JPL/NASA.

Eistla RegioComputer generated 3D perspective of a portion of western Eistle Regio. Gula Mons, the volcano on the right horizon reaches 3 km high while Sif Mons, the volcano on the left horizon has a height of 2 km. The imaging and altimetry data collected by Magellan are combined to produce this image.

Credit: Magellan, E. De Jong, J. Hall and M. McAuley-JPL/NASA.

north pole view of VenusGlobal view of northern hemisphere. The north pole is at the center of the image. Ths image is produced mostly from Magellan's measurements which has mapped 98% of the surface. Remaining gaps are filled from other measurements (Arecibo radio telescope, Venera missions etc.).

Credit: Magellan, JPL/NASA

Venus in UVUltra-violet (UV) image of Venus taken by HST on Jan. 1995. The UV wavelengths trace out a horizontal Y-shape cloud pattern near the equator. The dark regions show the location of enhanced sulfur dioxide near the cloud tops. Because Venus is closer to the Sun than Earth, the planet appears to go through phases, like the Moon. When Venus swings close to Earth the planet's disk appears to grow in size, but changes from a full disk to a crescent.

Credit: HST, L. Esposito (University of Colorado, Boulder), and NASA

Links


Magellan mission - Venus exploration during 1990-1994. Using radar to map out 98% of the Venusian surface.

Pioneer Venus project - Venus exploration missions consist of a Venus orbiter (ended in May 1992) and several small probes.

Everything about Venus - Venus data, other flybys, missions to Venus, images etc.

Venusian craters - More detailed description on impact craters on Venus.

Venusian volcanic features - More detailed description on various volcanic features (lavas, plains, volcanos etc.) on Venus.

Venus, Earth comparison - Fact sheet comparison between Venus and Earth.

Mercury Planet Earth

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