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VENUS VENUS Venus, the jewel of the sky, was once know by ancient astronomers as the morning star and evening star. Early astronomers once thought Venus to be two separate bodies. Venus, which is named after the Roman goddess of love and beauty, is veiled by thick swirling cloud cover. Astronomers refer to Venus as Earth's sister planet. Both are similar in size, mass, density and volume. Both formed about the same time and condensed out of the same nebula Venus is very different from the Earth. It has no oceans and is surrounded by a heavy atmosphere composed mainly of carbon dioxide with virtually no water vapor. Its clouds are composed of sulfuric acid droplets. At the surface, the atmospheric pressure is 92 times that of the Earth's at sea-level. Venus is scorched with a surface temperature of about 482° C (900° F). This high temperature is primarily due to a runaway greenhouse effect caused by the heavy atmosphere of carbon dioxide. Sunlight passes through the atmosphere to heat the surface of the planet. Heat is radiated out, but is trapped by the dense atmosphere and not allowed to escape into space A Venusian day is 243 Earth days and is longer than its year of 225 days. Oddly, Venus rotates from east to west. To an observer on Venus, the Sun would rise in the west and set in the east. Venus spins retrograde (opposite) relative to the earth's movement Venus is never seen more than 47° from the Sun. Given Earth’s rotation rate of 15° per hour, this means that Venus is visible above the horizon for at most three hours before the Sun rises or after it sets. On a moonless night away from city lights, Venus casts a faint shadow. The planet’s brightness stems from the fact that Venus is highly reflective. Nearly 70 percent of the sunlight reaching Venus is reflected back into space Venus’s maximum brightness, as seen from Earth, actually occurs about 36 days before or after closest approach to our planet. At that time, Venus is about 39° from the Sun and 0.47 A.U. from Earth, and we see it as a rather fat crescent. Until just recently, Venus' dense cloud cover has prevented scientists from uncovering the geological nature of the surface. Developments in radar telescopes and radar imaging systems orbiting the planet have made it possible to see through the cloud deck to the surface below. Four of the most successful missions in revealing the Venusian surface are NASA's Pioneer Venus mission (1978), the Soviet Union's Venera 15 and 16 missions (1983-1984), and NASA's Magellan radar mapping mission (1990-1994). As these spacecraft began mapping the planet a new picture of Venus emerged. Venus' surface is relatively young geologically speaking The Venusian topography consists of vast plains covered by lava flows and mountain or highland regions deformed by geological activity. Maxwell Montes in Ishtar Terra is the highest peak on Venus. Sif Mons Venus Venus has more volcanoes than any other planet in the solar system Volcanoes and volcanic features are numerous. At least 85% of the Venusian surface is covered with volcanic rock. Hugh lava flows, extending for hundreds of kilometers, have flooded the lowlands creating vast plains. More than 100,000 small shield volcanoes dot the surface along with hundreds of large volcanos. Flows from volcanos have produced long sinuous channels extending for hundreds of kilometers, with one extending nearly 7,000 kilometers (4,300 miles). Over 1600 major volcanoes or volcanic features are known to exist the total number may be over 100,000 or even over 1,000,000 Large Shield Volcanoes Venus has over 150 large shield volcanoes One of the highest mountains on Venus is Maats Mons which reaches to 8 km (5 miles) above the mean venusian elevation: This rendition of Sif Mons, about 2 km (1.2 miles) high and covering an area of nearly 300 km (200 miles) in diameter, Sif and Gula Mons Sif and Gula seem to be hotspot volcanoes like those in Hawaii Sapas Mons Sapas is 1.5 km high and is about 120 km across Unlike many large shields on Venus, Sapas does not lie on a major rift structure Radar is brightest over rough, blocky surfaces; thus, this range of color suggests a change in volcanism over time. Namely, the youngest lavas are fairly bright, but the older lavas seem to be much smoother, especially in the band of dark lavas along the lower right edge of the volcano Ushas Mons Ushas Mons lies in the southern hemisphere on the northern part of Dione Regio It is surrounded by volcanic plains with many small shields (especially in the upper left and lower right). Also note the clear north-south faults running unde r the volcano. These seem to have formed with the volcano, and may contain volcanic dikes Ushas is over 500 km across, and is about 2 km high Theia Mons/Devana Chasma Theia Mons is the largest volcano on Venus It is over 4 km high, and its lava flows cover an area more than 800 km wide. It has an oval central caldera roughly 75 km long and 50 km w ide. The volcano also lies at the junction of 3 major rifts, one of which is seen here running off the top of the image. This rift, Devana Chasma, is over 200 km wide, but it narrows down to ~50 km as it climbs Venus is scarred by numerous impact craters distrubuted randomly over its surface. Small craters less that 2 kilometers (1.2 miles) are almost non-existent due to the heavy Venusian atmosphere. The exception occurs when large meteorites shatter just before impact, creating crater clusters. Danilova Crater -26.4° Latitude, 337.2° Longitude; 49 kilometers (30 miles) diameter; central peak crater The first image shows the Venusian impact crater Danilova as seen by the Magellan spacecraft. The crater has a central peak, a crater wall, a crater floor, an ejecta blanket, and crater outflow deposits. The second image is a geologic sketch map of the crater. (Copyright Calvin J. Hamilton) Mead Crater Yablochkina Crater Phases of Venus: Are just like the phases of the moon, but observed differently