Friday, September 9, 2016

NASA Launches Mission To Retrieve Ancient Asteroid Dust

   The goal: Bring back ancient dust.

   The asteroid is called Bennu, and it's basically a giant rubble pile, shaped something like a spinning top. But it's a very special rubble pile. Scientists believe it has been moving through space untouched for about 4.5 billion years, making it a time capsule from when our solar system was just starting to form.
   That's why astrophysicist Christina Richey is excited to get a robot there.

  "That's a level of understanding we don't have on Earth right now, and that's something we really need," says Richey. She's one of the people at NASA coordinating the mission, which is called OSIRIS-REx — short for "Origins, Spectral Interpretation, Resource Identification, Security – Regolith Explorer."

   She and other scientists think that asteroids such as this one might have delivered carbon-containing compounds to Earth long ago that helped the planet give rise to life.

   If everything goes as planned, a minivan-sized robot, moving oh-so-slowly, will lightly graze the asteroid in mid-2018. It'll inhale somewhere between a few tablespoons and a few pounds of dust and gravel.

  "We're expecting there to be — basically — dirt," Richey says.

In 2010, a Japanese mission also brought back a sample — a tiny one — from an asteroid. Part two of that mission is now en route to collect material from another asteroid, with an intended return date in 2020. And in 2006, NASA's Stardust mission scooped up ancient dust from a comet.

  "This is kind of like a follow-on to Stardust," Richey says, "only with a way larger sample and with an asteroid versus a comet."

   If all goes as planned, scientists will have in hand the dirt from Bennu in 2023, when the capsule holding the sample leaves the spacecraft and makes a parachute landing in the Utah desert.

  "I'm really keen on getting the sample back, having it be pristine and getting to really understand fundamentals of our solar system," Richey says.

   Planetary scientist Michael Drake, who led the OSIRIS-REx team until he became ill with cancer and died in 2011, told The New York Times that year that he hoped the mission would help answer some big questions: "Where do we come from? How did we come to exist? What's the origin of the organic material that provided the building blocks that led to life?"

   And there's another reason scientists are interested in Bennu, and have been tracking it for 20 years: There is a tiny chance that the asteroid could whack into Earth around the end of the next century.

   Don't panic — there's a 99 percent chance that won't happen. Still,   Bennu is officially considered a "potential hazard to Earth." (NASA's Potentially Hazardous Asteroids list includes any object that's big enough to cause damage, even after burning through the Earth's atmosphere, and that will come within 5 million miles of the Earth's orbit.)

  "So, we'll have over 20 years of very precise tracking data on this asteroid," says Dante Lauretta, a planetary scientist at the University of Arizona in Tucson and the principal investigator for OSIRIS-REx.

Lauretta says the mission, which is expected to cost $800 million excluding the launch, will closely monitor the asteroid's path and help confirm whether scientists' predictions about its trajectory are correct.

   There's one thing in particular they want to get a handle on that can make asteroid movement hard to predict. It's called the Yarkovsky effect, and it goes something like this: Anything close to the sun, including Bennu, absorbs sunlight and then later releases that energy. "So it gets that energy from the sun and it pushes that energy back out," Lauretta explains.

   That subtle burst of energy could be enough to nudge an asteroid's path closer to Earth.

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

   Between the Yarkovsky effect and a path-bending pass by the moon in 2135, NASA estimates that Bennu has a 1-in-2,700 chance of changing its course just enough to slam into Earth sometime between 2175 and 2199.

   Lauretta and his colleagues want to confirm their projection so they can better predict the paths of other near-Earth objects that have a chance — however slim — of causing some serious damage to our planet.

   So, before zooming in for the dirt sample, OSIRIS-REx will circle the asteroid for two years, measuring how much energy Bennu absorbs and releases, and how that changes its predicted path.
  "We've always had the tagline of OSIRIS-REx of 'Exploring our past and securing our future,' «Lauretta says, "and I think we're going to do both of those."


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