One of the most exciting new fronts in space travel is asteroid sample returns. Following the Stardust comet sample returns of last decade, as well as the increasing likelihood of near-future efforts to mine precious metals and other resources from our system’s asteroids, means that we should probably start learning just how to pull off such a maneuver.

Asteroid Bennu is one of our best first candidates and the target of NASA’s OSIRIS-Rex mission. It zips quite close to earth every few years (and may even one day collide with our planet), and scientists suspect that it could contain the building blocks for life — making it an ideal target for astrobiologists and geologists alike.

Credit: United Launch Alliance

Bennu is a carbonaceous asteroid, meaning that it absorbs lots of the sun’s radiation which, in turn, affects its orbit. As a B-class asteroid like Bennu contains materials that date back to the very early solar system, including volatile organic compounds, amino acids, and other basic structures that life needs. Studying it, then, could yield new information about what sorts of material early had to work within the solar system. That could give us key clues as to what earth and other celestial bodies looked like four billion years ago.

At the same time, Bennu will pose some unique challenges when the OSIRIS-Rex craft arrives next year. For starters, it’s essentially a “rubble pile,” according to NASA, made up of a loosely-bound agglomeration of boulders, soil, dust, and rock. At half a kilometer wide, it’s just large enough to be bound by gravity, but not much more. That instability means landing isn’t the best plan. Instead, the craft will hold close by and attach an arm that scoops up some of the surface material for a return.

This mission is also important because Bennu is one of the largest medium-term threats to life on Earth. It has a better than 1-in-3000 chance of hitting us in the late 2100s, and a core part of the mission will be to study the exact effects that the soil and rock type have on the asteroid’s orbit, giving us better tools for estimating where it might hit down the line.

The Yarkovsky effect, in particular, is of prime concern. As the rock orbits in the solar system, solar radiation and winds can affect the trajectory, based on a number of material properties of the asteroid. Measuring exactly what it’s made of should give us the tools to refine our estimates and better discern if Bennu will be a threat.

“By bringing this material back to Earth, we can do a far more thorough analysis than we can with instruments on a spacecraft, because of practical limits on the size, mass, and energy consumption of what can be flown,” Edward Beshore, deputy principal investigator at the University of Arizona told “We will also set aside returned materials for future generations to study with instruments and capabilities we can’t even imagine now.”

OSIRIS-Rex should arrive at Bennu next year, and, if all goes well, safely return to Earth by 2023 with a sample. Leaving us almost 200 years to figure out whether Bennu will hit us and what we might need to do about it. Plenty of time, right?


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