VOA常速英语:Mercury Spacecraft Reveals New Details of Mysterious Planet

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U.S. space scientists on Wednesday revealed new information about Mercury, the solar system's smallest and hottest planet. The data were collected by the U.S. space agency's MESSENGER space probe that, for the second time this year, zipped past the heavily cratered planet closest to the Sun. VOA's Jessica Berman reports.

The battered surface of Mercury came into clearer focus for scientists after they analyzed the 1,200 images taken on October 6, during the second flyby of MESSENGER, which stands for Mercury Surface, Space Environment, Geochemistry and Ranging.

Astronomers say the new region of Mercury they viewed at close range is bigger than the land area of South America, revealing 30 percent of the tiny planet never before seen.

Between the flyby and an earlier one in January, and data collected by Mariner 10 in the early 1970s, scientists have now seen at least 90 percent of Mercury.

The latest images bring into sharper focus the craters that pockmark the planet's surface as well as smooth planes. Space scientists say it appears that most of the craters were caused by volcanic activity rather than impacts by space debris.

"Most of the action we think happened in the very earliest history [of the planet]," said Maria Zuber of the Massachusetts Institute of Technology, a MESSENGER co-investigator. "And we don't know the absolute date because we haven't been able to sample the rocks. But when we think about that, we think on the order of 3.8, 3.9, four billion years ago."

Scientists also compared data gathered during MESSENGER's first and second flybys of Mercury's magnetosphere and the planet's thin atmosphere, called the exosphere.

"Everybody is really anxious to get into orbit, to get real data," said Marilyn Lindstrom, MESSENGER's program scientist.

The two flybys offered critical gravity assists to MESSENGER that will put the space probe into permanent orbit around Mercury in 2011.