NASA wants dirt, gravel from the asteroid Bennu but its bumpy surface poses problems

NASA scientists said Tuesday they believe they can overcome a snag in the space agency’s first-ever mission to collect dirt and gravel from an “active asteroid.”

NASA’S Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) has been circling the asteroid Bennu, 70 million miles from Earth, since Dec. 31 in search of place to operate.

Scientists had thought the 535-yard-wide, diamond-shaped asteroid had flat areas where OSIRIS-REx would be able to gather up samples.

But images from the spacecraft show that Bennu’s surface is covered with rocks much larger than they had expected, with more than 200 measuring some 32 feet in diameter.

The asteroid also is spraying out particle plumes, which is rare and makes the massive space boulder “active” in NASA-speak.

“That [ruggedness] definitely caught us by surprise,” Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona at Tucson, said in a conference call with reporters. “The discovery of plumes is one of the biggest surprises of my scientific career.”

Bennu’s rocky face and spray of particles complicate the mission of OSIRIS-REx’s sample collector, known as Touch-and-Go (TAG), because it was designed for a smoother, less volatile surface. TAG uses a 10-foot-long sampling arm, which spits out a puff of gas to disturb dust and small rocks, which it then vacuums up.

NASA scientists now are scrambling to find a large, smooth spot on Bennu’s surface for OSIRIS-REx to work.

Lori Glaze, the agency’s director of planetary science, said she is “confident that the scientists and engineers will retrieve a sample of Bennu,” adding that NASA is used to dealing with missions that require “surprises, quick thinking and doing what it takes to get good science.”

Details about the $800 million mission’s observations were published Tuesday in the science journals Nature, Nature Astronomy, Nature Geoscience and Nature Communications.

Other highlighted findings included that Bennu contains hydrated minerals, including magnetite, which could indicate that the asteroid once had water.

The asteroid is the smallest space object orbited by a spacecraft. It also is older than scientists had estimated, between 100 million and 1 billion years old. They speculate that it broke off from the asteroid belt between Jupiter and Mars a couple of billion years ago, then hurtled through space and settled in an orbit closer to Earth.

Engineers also note that Bennu’s rate of spin is increasing because of what scientists call the Yarkovsky-O’Keefe-Radzievskii-Paddack effect.

Engineers said they did not know why the small particles, some of which are smaller than an inch wide, are randomly spewing from Bennu. Some have been observed falling back onto the surface, while others drift into interstellar space. Mr. Lauretta speculated they could be bits of ice vaporizing as the plume sprays outward.

Japan gathered the first asteroid sample in 2010 and is attempting a second collection from an asteroid named Ryugu.

OSIRIS-REx is scheduled to collect its dust sample in July 2020 and return it to Earth when it lands in the Utah desert in 2023.

• This article is based in part on wire service reports.