Asteroid Profile: 101955 Bennu

With NASA’s OSIRIS-REx poised for launch on Sept. 8, Dr. John S. Lewis, chief scientist at Deep Space Industries, explores its mission target, the near-Earth asteroid Bennu.

It’s called Bennu. And scientists have been waiting for a long time to get their hands on it.
Scheduled for a September 8 launch, NASA is set to embark on its first asteroid sample return mission. Their deep space explorer, OSIRIS-REx, is the third spacecraft in NASA’s New Frontiers Program. The other two include the wildly successful New Horizons mission to Pluto last year, and spacecraft Juno’s historic long-term orbit of Jupiter which began in August.

Over the next seven years, OSIRIS-REx will rendezvous with near-Earth asteroid Bennu and hover over it while scanning its surface. Then, after more than a year, the spacecraft will finally swoop in, scoop up some soil, and return the batch to Earth. And to the welcoming arms of the scientists (see infographic timeline).

These scientists are counting on the 2- to 70-ounce sample to tell them more about how our solar system was formed. They hope that Bennu’s soil will show how the solar system works, and what resources and hazards similar asteroids contain.

But why not simply study the thousands of meteorites we’ve collected on Earth for these answers?

Terrestrial contamination. Scientists consider Bennu’s sample “pure”. Meaning, taken from the source, it remains as it was when the solar system was formed — a kind of celestial snapshot — and entirely without the taint of Earth entry and contact with microbes.

It’s interesting to note that just as NASA did with the lunar material returned during the Apollo missions, they will preserve at least 75% of the Bennu sample for future scientists to analyze in the decades to come.

“In the near-Earth asteroid realm, Bennu is sort of an odd duck”, says Dr. John S. Lewis, chief scientist at DSI and author of Asteroid Mining 101, the industry’s definitive book on space resource mining.

“Bennu’s reflectivity is strikingly low, only 4.6% of the incident sunlight gets reflected. The amount of really useful spectral information is small from here on Earth.”

And as a member of the relatively rare Class-B carbonaceous chondrite type, Dr. Lewis expects Bennu to contain minerals such as silicates, water-bearing clay minerals, black organic polymers, magnetite, and sulfides.

“Its density is very low so a volatile-rich composition is reasonable.”

On whether Bennu would make a suitable target for resource mining in space, Dr. Lewis explains that, “One of the main results of the OSIRIS-REx mission will be to verify that our somewhat sketchy spectral interpretation is valid. Both through in situ studies and sample return to Earth.”

“If the present evidence holds up to closer scrutiny, Bennu would be a rather accessible target for making propellant, like water. A reasonable guess would be that Bennu could provide a couple million tons of water and a similar amount of organic matter.”

But, Bennu presents a darker side. As an Apollo – an asteroid whose orbit crosses Earth’s – Bennu remains an impact threat to our planet. According to Dr. Lewis, a collision might be equivalent to 1000 megatons of TNT. Yet at the same time, Bennu, “appears to be a very weak body easily susceptible to breakup, both natural and artificial.”

Scientists predict that there are a series of eight potential Earth impacts by Bennu between 2169 and 2199.

“Bennu is not such a near-term threat,” Dr. Lewis cautions. “It appears that we will have plenty of time to use Bennu’s own resources to protect ourselves from it by diverting its course, using it up through mining, or breaking it up into smaller, less dangerous pieces.”

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