Venus: Magellan Mission | p32876 | ||
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NASA's
Magellan spacecraft used a sophisticated imaging radar to make the most
highly detailed maps of Venus ever captured during its four years in orbit
around Earth's sister planet from 1990 to 1994. After concluding its radar mapping, Magellan also made global maps of Venus's gravity field. Flight controllers also tested a new maneuvering technique called aerobraking, which uses a planet's atmosphere to slow or steer a spacecraft. |
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Image Credit: NASA | |||
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Magellan
was the first planetary spacecraft to be launched by a space shuttle when
it was carried aloft by the shuttle Atlantis from Kennedy Space Center in
Florida on May 4, 1989. Atlantis took Magellan into low Earth orbit, where
it was released from the shuttle's cargo bay. A solid-fuel motor called
the Inertial Upper Stage (IUS) then fired, sending Magellan on a 15-month
cruise looping around the sun 1-1/2 times before it arrived at Venus on
August 10, 1990. A solid-fuel motor on Magellan then fired, placing the
spacecraft in orbit around Venus. Magellan's initial orbit was highly elliptical, taking it as close as 294 km from Venus and as far away as 8,543 km. The orbit was a polar one, meaning that the spacecraft moved from south to north or vice versa during each looping pass, flying over Venus's north and south poles. Magellan completed one orbit every 3 hours, 15 minutes. During the part of its orbit closest to Venus, Magellan's radar mapper imaged a swath of the planet's surface approximately 17 to 28 km wide. At the end of each orbit, the spacecraft radioed back to Earth a map of a long ribbon-like strip of the planet's surface captured on that orbit. Venus itself rotates once every 243 Earth days. As the planet rotated under the spacecraft, Magellan collected strip after strip of radar image data, eventually covering the entire globe at the end of the 243-day orbital cycle. |
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Magellan
returned maps of Venus's surface and its gravity field in unprecedented
detail that will be a resource for many years for scientists studying the
planet. The mission held many surprises for scientists, and resulted in
a number of theories about the planet being revised. From the craters visible in Magellan's Venus maps, scientists believe they are looking at a relatively young planetary surface, perhaps about 500 million years old. Since Venus formed at the same time as Earth 4.6 billion years ago, some event or events 500 million years ago must have resurfaced the planet. Scientists believe that this may have been the work of massive outpourings of lava from planet-wide volcanic eruptions. Although Venus may still have active volcanoes, no visible outpourings of lava have yet been detected in comparisons of Magellan images between one eight-month orbital cycle and another. Although some scientists speculate that Venus may have once been a temperate planet that fell victim to a runaway greenhouse effect creating enormously high temperatures, Magellan's maps show no telltale signs of past major water bodies such as shorelines or ocean basins. Also, surface features show no evidence of being eroded by water -- although there is evidence of wind erosion in the form of numerous sand dunes and wind streaks. One of the hopes that scientists had for Magellan was to find out if Venus, like Earth, has plate tectonics -- movements of crustal masses that on Earth cause earthquakes and result in the drifting of continents over time periods of hundreds of millions of years. They in fact found no evidence of plate tectonics in the data returned by the mission. Scientists suspect that, although Venus is very similar in size to Earth, its interior is probably different in major ways. |
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text credit: NASA | Return to top of page |