NASA picks the asteroid crater its spacecraft will steal rocks from next summer

Next year, NASA plans to scoop up a small batch of dirt from an asteroid named Bennu, located millions of miles from Earth — and now the agency knows which part of the space rock it’s going to steal from. Today, the space agency announced that one of its spacecraft will attempt to grab some particles from a 20-meter-wide crater, called Nightingale, on the asteroid.

Engineers picked the Nightingale site from four final candidate spots on Bennu, arguing it could be the best place to find organic material and water on the asteroid that may hail from the earliest days of the Solar System. “This one really came out on top, because of the scientific value,” Dante Lauretta, the principal investigator of the asteroid sampling mission, said during a press conference announcing the selection. However, targeting the crater is not without risk. The area is surrounded by a large wall of rocks, which could make it difficult to grab a sample. But ultimately, Lauretta said the area could have what they’re looking for.

Scientists are hoping to get a sample that will provide the best snapshot of what the early Solar System was like billions of years ago when it first formed. Asteroids are thought to be rocky remnants of the early Solar System, having stayed relatively the same over time and still containing materials that were present during the birth of the planets. Studying an asteroid’s offerings in a lab here on Earth could help us unlock some of the secrets of how our cosmic neighborhood came to be.

The robot tasked with grabbing and delivering these asteroid particles to our planet is the OSIRIS-REx spacecraft. The vehicle has been circling around Bennu for the last year, after spending two years traveling through space to reach the asteroid. During this hang out time, the spacecraft has been using various instruments to map Bennu’s surface and get a detailed understanding of what the rock’s terrain is like. That way, the engineering team behind OSIRIS-REx could pick the best site for the vehicle to sample.

Well, it turns out that Bennu is not a particularly amenable space rock. Almost immediately after OSIRIS-REx got to Bennu, NASA engineers realized that the asteroid was incredibly rugged and rocky. It’s quite different than what they thought it would be; based on their observations of the object from Earth, scientists thought that Bennu would house patches of smooth, sandy grains with very few boulders. Turns out there are hundreds of large boulders lurking on the asteroid, and smooth areas are almost nowhere to be seen.

That has made it extra tough to figure out the best place to grab a sample. To scoop up material from Bennu, OSIRIS-REx is equipped with a thin robotic arm that is meant to extend from the spacecraft and gently tap the asteroid, sending particles shooting up into the vehicle’s sample chamber. If OSIRIS-REx targets a particularly rugged patch, it could throw the sampler off or even cause the instrument to get clogged with large pieces of debris.

An image of the Nightingale crater, with a graphic of the OSIRIS-REx spacecraft’s size for scale
Image: NASA

The OSIRIS-REx team only gets one shot at sampling Bennu, so selecting this site was an incredibly important part of the mission. After mapping the surface, engineers scoured the images and used algorithms and software to find flat parts of Bennu. NASA even put out a call to the public to help find possible targets. After identifying 50 potential sites, the OSIRIS-REx team eventually whittled it down to four, finally landing on the Nightingale crater.

Nightingale is filled with lots of fine grain material, but it also has a few larger boulders, making it one of the riskier spots to target. But scientists think the risk is worth it. For one, the crater is located pretty far north on the asteroid, where temperatures are cooler than other areas. That’s extra enticing because the cold temperatures may have kept the material in the crater well preserved from the early days of the Solar System; the particles may not have changed dynamically over time from heating. Additionally, the OSIRIS-REx team thinks that the crater is relatively new, so the material within the region has actually been inside Bennu for a long time until being unearthed recently. That also means the material may have stayed relatively unchanged, since it hasn’t been exposed to the harsh radiation-filled space environment for very long.

Because Nightingale is a bit perilous, the OSIRIS-REx spacecraft has to be extra precise when it descends to the asteroid’s surface. The boulders surrounding the site could cause the spacecraft to tilt and then accidentally run into a rock as it tries to leave the asteroid. One of the rocks has even been nicknamed Mount Doom, since it’s extra tall and peak-shaped. “It’s a substantial building-sized obstruction, and we’re trying to get into a crater that’s on the order of a few parking lot spaces wide,” said Lauretta. “So we are doing a really tight job parking that, and we’re aware that we have hazards around us. So precision navigation to that sample material is our biggest challenge.” To be extra careful, the team has added some additional safety measures, programming the spacecraft to detect if it’s coming down on too rocky a surface. If so, it’ll fire its thrusters and fly away.

However, doing that will come with a cost. Firing thrusters on Nightingale may mess up the position of the material in the crater. If that does happen, the team will target a backup site called Osprey, which isn’t as scientifically exciting but a bit more smooth.

Currently, NASA is hoping to grab a sample from Nightingale in the summer of 2020, with the goal of collecting at least 60 grams of material. Once a sample is obtained, OSIRIS-REx will head back home in 2021 and attempt to land in the Utah desert in 2023. If the sample does contain water and organic material like the team hopes, it could reinforce the idea that asteroids like Bennu may have brought this material to Earth when it was freshly formed. And that could be a substantial piece of evidence for how life came to be on our planet.

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