LOS ANGELES – A NASA spacecraft will reach out and touch an asteroid and send pieces back to Earth, the space agency announced Wednesday.

The unmanned probe won’t land on the rocky body. But it will get close enough to kiss the surface and extend a robotic arm to grab up to 5 pounds of dust and organic material. The samples will be sealed in a capsule for the trip home.

Asteroids are considered leftovers from the formation of the solar system some 4.5 billion years ago. Studying them could shed light on the conditions of the infant solar system and how life emerged. These giant speeding rocks fly by Earth harmlessly most of the time, but have occasionally smacked the planet with disastrous results.

The $1 billion mission is set to launch in 2016 and will take four years to reach the asteroid and begin its study. The sample capsule will return to Earth in 2023.

The destination is an asteroid known as 1999 RQ36 after the year it was discovered. Because the asteroid — the size of five football fields across — changed little over time, it will give scientists a chance to study the origins of the solar system.

Chief scientist Michael Drake of the University of Arizona in Tucson described the asteroid as a “time capsule containing probably the building blocks of life.”

Though the Earth is full of meteorites, pieces of asteroids that constantly break away and make fiery plunges through the atmosphere, scientists are anxious to get samples that have not been contaminated.

“We’re bringing back something that’s essentially untouched by human hand,” he said.

While the mission is not directly related to White House plans to land astronauts on a different asteroid by 2025, information from this project will help the astronauts better understand what they are landing on, said Jim Green, director of NASA’s planetary science division.