WASHINGTON -- NASA's Pioneer Venus spacecraft, which has been orbiting Venus since 1978, apparently did not survive passage through the upper atmosphere of Earth's sister planet Thursday, officials announced Friday.
At 3:22 p.m. EDT Thursday, the craft passed through the lowest part of its orbit around Venus, which repeats every 24 hours, NASA said.
During this period, the radio signal could not be tracked from Earth because Pioneer was hidden behind Venus. No radio signal could be detected from the craft when it should have emerged from behind the planet, NASA said.
Pioneer was probably disabled by the heat of friction with the planet's atmosphere, with insulation and other fragile comonents melting or breaking off the craft, NASA said.
Although the craft's remains will continue to orbit Venus for a short time, no furthur data can be collected without the radio signal, NASA said.
Pioneer Venus made the first maps of Venus and has returned thousands of pictures of the planet over the past 14 years.
In many ways, Venus is Earth's twin in the solar system. Both planets are roughly similar in size and mass, both are relatively close to the sun and both probably were almost identical early in solar system history.
But somewhere along the way, the environments of Venus and Earth diverged, leaving Venus the victim of a runaway greenhouse effect in which the solar radiation trapped by the planet's thick cloud cover produces surface temperatures of 900 degrees -- hot enough to melt lead -- and pressures comparable to those found at an ocean depth of 2,500 to 3, 000 feet.
NASA subsequently sent the Magellan radar mapping probe to explore Venus.