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How NASA's trip to a small asteroid may answer big questions about the origins of life on Earth

OSIRIS-REx will launch Thursday from Florida, to visit an asteroid and return a sample to Earth. We preview the NASA mission.

Get ready for an interplanetary treasure hunt. On Thursday, NASA will launch its first mission to visit an asteroid and bring precious samples back to Earth.

OSIRIS-REx, set to launch around 7:05 p.m. EDT, will head to Bennu, a dark rubble-pile of an asteroid that stretches 492 meters (1,614 feet) wide. After the spacecraft reaches and orbits the near-Earth asteroid in 2018 and carries samples back to Earth, scientists hope to develop a detailed profile to shed light on the early evolution of the solar system, clues to the origin of life and tools that will enable them to accurately track asteroids that come uncomfortably close to Earth.

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The spacecraft, aboard an Atlas V rocket, was rolled out to the launch pad Wednesday morning. Jason Dworkin, the mission's project scientist, called the attitude among the team at Cape Canaveral "excited optimism."

"We're ready to go," Dworkin said in an interview, "and excited to see the spacecraft fly."

OSIRIS-REx (short for Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer) is bringing a suite of instruments that will help it understand Bennu in unprecedented detail. It will use several cameras to examine the surface, a laser altimeter to map the three-dimensional topography, visible- and infrared-light spectrometers to study the chemical and mineral composition and an X-ray spectrometer to study elemental abundances.

It also holds a pogo-stick-like arm with a disc-like device at the end that will carefully contact the surface and collect some of the dust and rock that scientists think cover Bennu's surface.

"We are basically a space vacuum cleaner," principal investigator Dante Lauretta said in a briefing Wednesday.

The eight known planets formed when the solar system was still in its infancy, coalescing out of the swirling disc of gas and dust that surrounded our nascent star. The asteroids are those bits of rock that never quite made it into one of these worlds; scientists think the belt of debris that stretches between the orbits of Jupiter and Mars could have been a planet, had the gas giant's gravity not kept it from forming.

These asteroids, then, are the leftover building blocks of the solar system — rocks that have never been altered by the heat and pressure inside a planet or been chemically transformed by the presence of life. As such, they hold clues to the early development of the solar system, including what it was made out of and what its dynamics were.

There are many different types of asteroids, but Bennu is particularly intriguing because its dark surface indicates that it's full of organic molecules, the kinds of chemicals that could have potentially seeded life on Earth.

Researchers have studied pieces of asteroids that have fallen to Earth as meteorites, but their searing plunge through the atmosphere and contact with the planet contaminate them, so that it's incredibly hard to tell which chemical clues are truly from the sample and which ones are merely terrestrial contamination.

OSIRIS-REx is not the first asteroid sample return mission — that honor goes to the Japanese Hayabusa mission, a spacecraft rendezvous that returned asteroid samples to Earth in 2010 — but it will bring back at least 60 grams of material, though it could potentially collect much more. Returned to Earth, the pristine sample could offer a trove of insight for generations of scientists to come, just as the moon rocks brought back by the Apollo missions in the 1960s and 1970s are still being studied today.

"Sample return is the gift that keeps on giving," Lauretta said in an August briefing.

Landing on a small object with little gravitational tug is no walk in the park (just ask the European Rosetta mission's Philae lander), because there's a tendency to bounce. So the spacecraft takes advantage of the bounce, making a five-second contact to collect the sample before pushing away.

The maneuver will be "a safe, smooth, slow high-five of that surface," Christina Richey, deputy program scientist in Washington, said in the August briefing.

Bennu will also allow scientists to study the Yarkovsky effect, a strange phenomenon that especially affects smaller, dark-colored asteroids. The asteroid's surface absorbs sunlight and then re-emits it later as heat, which acts like a thruster and can alter its course.

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This makes it difficult to predict an asteroid's path; for example, Dworkin pointed out, Bennu has veered about 100 kilometers (62 miles) off course since its discovery in 1999. Learning in detail how the Yarkovsky effect acts on Bennu could help scientists better predict the trajectories of other asteroids whose paths bring them within striking distance of Earth.

"If you want to be able to predict where an object like Bennu is going to be in the future, you have to account for this phenomenon," Lauretta said.

As it is with most interplanetary missions, patience is key: Scientists will have to wait to analyze the sample Bennu carries back to Earth; the spacecraft isn't slated to return its cargo until 2023.

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