Venus, second planet from the Sun and sixth in the solar system in size and mass. No planet approaches closer to Earth than Venus; at its nearest it is the closest large body to Earth other than the Moon. Because Venus’s orbit is nearer the Sun than Earth’s, the planet is always roughly in the same direction in the sky as the Sun and can be seen only in the hours near sunrise or sunset. When it is visible, it is the most brilliant planet in the sky. The greatest advances in the study of Venus were achieved through the use of robotic spacecraft. The first spacecraft to reach the vicinity of another planet and return data was the U.S. Mariner 2 in its flyby of Venus in 1962. Since then, Venus has been the target of more than 20 spacecraft missions. Successful early Venus missions undertaken by the United States involved Mariner 2, Mariner 5 (1967), and Mariner 10 (1974). Each spacecraft made a single close flyby, providing successively improved scientific data in accord with concurrent advances in spacecraft and instrument technology. After visiting Venus, Mariner 10 went on to a successful series of flybys of Mercury. In 1978 the United States launched the Pioneer Venus mission, comprising two complementary spacecraft. The Orbiter went into orbit around the planet, while the Multiprobe released four entry probes—one large probe and three smaller ones—that were targeted to widely separated points in the Venusian atmosphere to collect data on atmospheric structure and composition. The Orbiter carried 17 scientific instruments, most of them focused on study of the planet’s atmosphere, ionosphere, and interaction with the solar wind. Its radar altimeter provided the first high-quality map of Venus’s surface topography. Pioneer Venus Orbiter was one of the longest-lived planetary spacecraft, returning data for more than 14 years.
Posted on: Mon, 01 Sep 2014 11:52:46 +0000
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