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Astronomy Now OSIRIS-REx captures its first images of asteroid Bennu

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An artist’s impression of the OSIRIS-REx spacecraft during an attempt to collect soil and rock from the surface of asteroid Bennu. The spacecraft is expected to slip into orbit around the asteroid at the end of the year. Image: NASA

Two years after launch, NASA’s OSIRIS-REx spacecraft has snapped its first pictures of asteroid Bennu, setting the stage for a cautious step-by-step approach and rendezvous designed to put the probe in orbit around its quarry on New Year’s Eve. After a full year of close-range observations to map the asteroid, measure its gravity field and determine its composition, the spacecraft will attempt to collect rock and soil samples that will be returned to Earth for detailed laboratory analysis.

Principal Investigator Dante Lauretta of the University of Arizona said OSIRIS-REx captured five initial images of Bennu on 17 August at a distance of 2.18 million kilometres (1.4 million miles), showing the 500-metre-wide (1,600 feet) asteroid as a point of 13th magnitude light moving across a field of equally dim stars.

“I can’t explain enough how much it meant to this team,” Lauretta said during a teleconference with reporters on 24 August. “I know Bennu is only a point of light here, but many of us have been working for years and years and years to get this first image down, and it really represents the beginning of the great scientific expedition that is OSIRIS-REx.”‘

The images showed the asteroid “was right where we thought it was, so it’s there and it’s waiting for us,” he said. “The spacecraft was also where it was supposed to be and pointing in (the right) direction, so our navigation team has done a fantastic job getting us on this approach trajectory.”


Asteroid Bennu is seen here, circled in green, as it moves across a starfield on 17 August. The images were captured by NASA’s OSIRIS-REx spacecraft at a distance of 2.2 million kilometres (1.4 million miles. Image: NASA

Bennu was discovered in 1999 in an orbit that carries it across Earth’s. It is one of the most potentially hazardous asteroids yet detected with a 1-in-2,700 chance of hitting Earth late in the 22nd century.

The $1 billion OSIRIS-REx mission is designed to map Bennu in enormous detail, using a laser-ranging system to chart the asteroid’s topography, three cameras to characterise surface features and its spectrometers to tease out details of Bennu’s chemical composition. In so doing, scientists will collect data shedding light on how an asteroid on a collision course with Earth might be diverted or broken apart.

But the highlight of the OSIRIS-REx mission will come in 2020 when the spacecraft will descend to within a few metres of Bennu’s surface, pushing a collector on the end of a 3-metre-long (10-foot) robot arm onto the surface to collect up to 2 kilograms (4.4 pounds) or rock and soil. If all goes well, the sample will be returned to Earth in 2025 for detailed laboratory analysis.

Lauretta said the spacecraft should begin resolving features on Bennu’s surface in October. Starting 3 December, OSIRIS-REx will begin flying in formation with the asteroid before slipping into orbit at the end of the month.

That milestone is just one of three major encounters coming up for NASA spacecraft this fall. The agency’s InSight Mars lander is is on course for touchdown on the red planet 26 November to explore the deep interior of the red planet.

And within hours of OSIRIS-REx reaching orbit around Bennu on 31 December, NASA’s New Horizons probe will streak past a small Kuiper Belt object nicknamed Ultima Thule on New Year’s Day, giving scientists a close-up look at a chunk of debris left over from the birth of the solar system some 4.6 billion years ago. New Horizons completed its primary mission objective in 2014 when it flew past Pluto.

“It’ll be the season of science, we will be enjoying every minute of it, and it’ll be a great time for all of us,” said Lori Glaze, acting director of NASA’s Planetary Science Division. “I hope everyone’s ready to stay up all night on the 31st and enjoy the whole package.”

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