VOA慢速英语2015 美国黎明号航天器,接近矮行星（在线收听）

NASA Spacecraft, Dawn, Close to Reaching a 'Dwarf Planet' 美国黎明号航天器,接近矮行星

An American spacecraft is moving closer to a dwarf planet called Ceres. The American space agency’s Dawn spacecraft is set to reach the planet-like object in March.

Space agency scientists will then place Dawn in an orbit around the dwarf planet. Agency scientists want to know more about ice on Ceres. The spacecraft will gather clues about whether Ceres may have once had conditions to support life as we know it.

Dawn left Earth more than seven years ago on a trip to explore Ceres and another dwarf planet, called Vesta. Both dwarf planets are in the main belt of asteroids, a group of large objects, between the planets Mars and Jupiter.

Marc Rayman is the chief engineer and director of the Dawn mission.

“This is the first time in more than 57 years of space exploration that we have a spacecraft targeted to orbit any two extraterrestrial destinations.”

Scientists call Vesta and Ceres “protoplanets.” Mr. Rayman says they were in the process of becoming full-size planets when, in his words, “their growth was terminated.”

Scientists believe Ceres is made of rock, and covered with ice. 

The Dawn mission is based in Los Angeles, California. Scientists there send second-by-second commands to the spacecraft. They direct its every move, including telling it what pictures to take. Dawn will make a map of the dwarf planet. It will also try to discover how Ceres’ surface has changed.

Carol Raymond is the deputy principal investigator of the project.

“One of the interests in bodies like Ceres and other icy bodies in the outer solar system is that when objects like that impacted the terrestrial planets, they brought a lot of water. So there’s a very vigorous debate at the current time as to whether wet asteroids like Ceres -- and we know there are other wet asteroids in the outer edge of the main belt -- whether they were the dominant source of water in the Earth’s ocean.”

Carol Raymond says Dawn made an unexpected discovery while orbiting Vesta.

“Instead of being bone dry, which we expected, there were patches on the surface of Vesta that showed significant amounts of water bound in the rocks and possibly even free water that could have flowed on the surface in the past.”

She says that if Earth’s water came from wet worlds like Vesta and Ceres, then life could have developed there, too.

If Dawn finds that the environment of Ceres could have supported life, scientists may seek to explore the dwarf planet with other scientific instruments.

Dawn will gather information about Ceres until the middle of 2016. It will then continue to orbit the small planet.

Words in This Story

orbit – n. the curved path that something (such as a moon or satellite) follows as it goes around something else (such as a planet)

belt – n. a region that has a lot of a particular thing

asteroid – n. any one of thousands of small planets that circle around the sun

extraterrestrial – adj. coming from or existing outside the planet Earth

protoplanet – n. a mass of material within a planetary disk that is thought to be an early stage in the formation of a planet; a hypothetical whirling gaseous mass within a giant cloud of gas and dust that rotates around a sun and is believed to give rise to a planet

terminate(d) – v. to cause (something) to end

body(ies) – n. an object that is separate from other objects

impact(ed) –  v. to hit (something) with great force

terrestrial – adj. relating to or occurring on the earth

vigorous – adj. done with great force and energy

dominant – adj. more important, powerful, or successful than most or all others

bone dry – idiom very dry; no moisture

patch(es) – n. a small spot or area that is different from the surrounding area

significant – adj. very important

bound – scientific located in; a part of

sophisticated – adj. highly developed and complex