OSIRIS-REx spacecraft will eventually scoop up material for analysis back home
After a two-year chase, a
NASA probe has reached the ancient asteroid
Bennu. The robotic explorer Osiris-Rex pulled within 12 miles (19km) of the diamond-shaped object on Monday and will go into orbit around it on 31 December. No spacecraft has ever orbited such a small body.
Bennu is considered a potentially hazardous asteroid – it is due to make a close pass of Earth about 150 years. If it collided with Earth, Bennu would probably cause a crater.
Osiris-Rex aims to collect at least 60 grams (two ounces) of dust and gravel, the first such attempt by the US after a smaller mission to another asteroid by Japan.
The spacecraft won’t land but use a three-metre mechanical arm in 2020 to momentarily touch down and pick up particles. The sample container is planned to break loose and head toward Earth in 2021.
The collection – parachuting down to Utah – would represent the biggest such haul since the Apollo astronauts hand-delivered moon rocks to Earth in the late 1960s and early 1970s.
Scientists hope to learn more about the source of water in the solar system and the origins of organic molecules from which life first arose. Getting their hands on pristine asteroid material might also yield clues about how to mine them for valuable materials and defend against wayward ones that might threaten Earth.
Flight controllers applauded and exchanged high-fives on Monday once confirmation came through that Osiris-Rex made it to Bennu – exactly one week after Nasa landed a spacecraft on Mars.
“Relieved, proud, and anxious to start exploring!” tweeted lead scientist Dante Lauretta of the University of Arizona. “To Bennu and back!”
Bennu is 76m miles (122m km) away so it took seven minutes for word of the success to reach flight controllers at Lockheed Martin in Littleton, Colorado, where the spacecraft was built.
Bennu is estimated to be just over 1,600ft (500 metres) across. Researchers will provide a more precise description at a scientific meeting on Monday next week in Washington.
About the size of a large car, the spacecraft will shadow the asteroid for a year, before scooping up some gravel for return to Earth in 2023.
A Japanese spacecraft, meanwhile, has been hanging out at another near-Earth asteroid since June, also for samples. It is Japan’s second asteroid mission. This latest rock is named Ryugu and is about double the size of Bennu.
Ryugu’s specks should be here by December 2020 but will be far less than Osiris-Rex’s promised booty.
Nasa has brought back comet dust and solar wind particles before but never asteroid samples. Japan managed to return some tiny particles in 2010 from its first asteroid mission, named Hayabusa.
Contact with Bennu will not significantly change its orbit or make it more dangerous to Earth, Lauretta stressed.
The $800m Osiris-Rex mission began with a 2016 launch from Cape Canaveral, Florida. Its odometer read 1.2bn miles (2bn km) as of Monday.
Both the spacecraft and asteroid’s names come from Egyptian mythology. Osiris is the god of the afterlife, while Bennu represents the heron and creation.
Osiris-Rex is actually a Nasa acronym for origins, spectral interpretation, resource identification, security-regolith explorer.