VOA标准英语2013--欧洲太空总署绘制银河系的3D地图（在线收听）

ESA to Make 3D Map of Milky Way 欧洲太空总署绘制银河系的3D地图

The European Space Agency this week successfully launched the star-mapping satellite Gaia on a mission that will take it more than a million kilometers from Earth - to  create the first three-dimensional (3D) map of our galaxy, the Milky Way.

The two-ton satellite, launched from the European Space Agency’s center in French Guiana aboard a Russian Soyuz rocket, reached the initial orbit and deployed a 10- meter circular sunshield to keep the instruments on-board, including a telescope, cool.  In order to focus on very distant and faint stars, Gaia has to be mechanically  and thermally stable, so it has almost no moving parts.

Mark McCaughrean, the mission's chief scientist, says, “It will measure the positions of a billion stars but also their speeds, their motions. And with that we can  run a movie of the Milky Way.  We can run it forwards, into the future, how the Milky Way will develop by looking at all the stars and how they move. But we can run it  backwards as well, and we can see how the Milky Way actually formed in the first place.”

Gerard F. Gilmore, a professor at Cambridge University's Institute of Astronomy, says the three-dimensional picture will eventually cover half of the Milky Way and  provide new knowledge about what keeps it together.

“And the particular interest that I have in here, locally, is in the nature of dark matter," he said. "What is dark matter made of? Dark matter is most of the weight  in the Milky Way. It is dark matter that holds the Milky Way together. If there weren′t all this dark material, our sun would fly off...away from the galaxy. The  whole galaxy would fall apart.”

The Gaia satellite will be moved to a distance of 1.5 million kilometers from Earth, to a gravitationally stable point called L2, where it will start its five-year  mission of taking approximately 70 images of each star in our galaxy, building a catalog of about one billion stars.

L2 is also designated as the parking space for NASA’s supersensitive infrared James Webb Space Telescope, scheduled for launch in 2018.

The overal cost of the Gaia mission is around $1.3 billion.