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Venus • Venus is the second planet from the Sun. As seen from Earth, it is the brightest object in the sky except for the Sun and the Moon. • Of all the planets in the solar system, Venus is most similar in size to Earth. Its mass is 82 percent of Earth’s mass, and its diameter is 95 percent of Earth’s diameter. • Venus orbits the Sun in 225 Earth days. It rotates in 243 Earth days. Unlike most other planets, Venus rotates and orbits in opposite directions. The combination of its rotation and orbit leads to very long days and nights. On Venus, there are two months of daylight followed by two months of darkness. • Venus has a very dense atmosphere. The air pressure on Venus is about 90 times the air pressure on Earth. The gas that makes up most of Venus’s atmosphere is carbon dioxide. This carbon dioxide gas holds in heat, causing the planet’s surface to reach temperatures of over 470°C (870°F). • Due to characteristics of its atmosphere, Venus is evenly heated. Nights are as warm as days, and temperatures at the northern and southern poles are the same as temperatures at the planet’s equator. Because of Venus’s high temperature, liquid water does not exist on the planet. • Venus is covered by clouds of sulfuric acid that hide the planet’s surface from view. • Venus’s cracked surface was formed by the movement of tectonic plates. Much of Venus’s surface is also covered by lava, the result of erupting volcanoes, which can also be seen on the planet’s surface. • Venus has been the subject of several unmanned space probes. The first successful crash-landing of a probe occurred March 1, 1966, when the Soviet Venera 3 probe arrived on the planet’s surface. The Venus Express Probe, designed by the European Space Agency and launched by a Russian rocket, made its first successful orbit of the planet on April 11, 2006. The scientific mission to study the planet’s atmosphere and clouds is expected to last around two Venusian years (about 500 Earth days). Copyright © Holt McDougal/Houghton Mifflin Harcourt.