美国国家公共电台 NPR NASA Launches Mission To Retrieve Ancient Asteroid Dust（在线收听）

NASA Launches Mission To Retrieve Ancient Asteroid Dust 

play pause stop mute unmute max volume 00:0003:12repeat repeat off Update Required To play the media you will need to either update your browser to a recent version or update your Flash plugin. STEVE INSKEEP, HOST: 

Tonight, a rocket launches from Cape Canaveral, Fla. NASA and the University of Arizona are sending a robot to an asteroid that passes by us every six years. They're hoping to gather samples from that asteroid that offer clues to the origin of life. Here's NPR's Rae Ellen Bichell.

RAE ELLEN BICHELL, BYLINE: The asteroid is called Bennu, and it's basically a giant rubble pile shaped something like a spinning top, but the rubble is very special. Scientists think it's been there, untouched, for about 4 and a half billion years, making it a sort of time capsule. That's why Christina Richey is excited to get a robot there.

CHRISTINA RICHEY: That's a level of understanding we don't have on Earth right now, and that's something we really need.

BICHELL: Richey is one of the people at NASA coordinating the mission, which is called OSIRIS-REx. She and other scientists think that long ago, asteroids like this one may have crashed into Earth, delivering organic compounds that turned it into a habitable place for life. If everything goes as planned, a minivan-sized robot will lightly graze the asteroid in mid-2018. It'll inhale somewhere between a few tablespoons and a few pounds of dust and gravel.

RICHEY: We're expecting there to be basically dirt.

BICHELL: A few years ago, a Japanese mission brought back a teeny tiny sample from an asteroid. And in 2006, a NASA mission, called Stardust, plucked ancient dust from a comet.

RICHEY: This is kind of like a follow-on to Stardust only with a way larger sample and with an asteroid versus a comet.

BICHELL: Scientists expect to have that sample in 2023.

RICHEY: I am really keen on getting the sample back and having it be pristine and getting to really understand the fundamentals of the origins of our solar system.

BICHELL: But there's another reason scientists are interested in Bennu. There is a tiny chance that the asteroid could whack into Earth around the end of the next century. Now, there's a 99 percent chance that won't happen, but Bennu is still considered a potential hazard to Earth. That's one reason why scientists have been tracking it for years.

DANTE LAURETTA: Now, we'll have over 20 years of very precise tracking data on this asteroid.

BICHELL: That's Dante Lauretta, a planetary scientist at the University of Arizona and the principal investigator for OSIRIS-REx. Lauretta says the mission will closely monitor the asteroid's path and help confirm if scientists' predictions about its trajectory are correct. There's one thing in particular they want to get a handle on, it's called the Yarkovsky effect. It's one thing that can make asteroid movement hard to predict.

LAURETTA: We've realized that it's a dominant factor in moving the orbits of these small, sub-kilometer asteroids through the solar system.

BICHELL: The idea goes like this, anything close to the sun, including Bennu, absorbs sunlight and then later releases that energy.

LAURETTA: So it gets that energy from the sun, and it pushes that energy back out.

BICHELL: And that subtle burst of energy could be enough to nudge an asteroids path closer to Earth. Loretta and his colleagues want to confirm their projection so they can better predict the paths of near-Earth objects that have a chance, however slim, of causing some serious damage to our planet. So before scooping up that dirt sample, OSIRIS-REx will circle the asteroid for two years measuring how much energy it absorbs and releases and how that changes its path.

LAURETTA: We've always had the tagline of exploring our past and securing our future, and I think we're going to do both of those.

BICHELL: That is, if the mission goes as planned. Rae Ellen Bichell, NPR News.