Bennu - Photo via Wikimedia Commons

A 3D-printed model of the Bennu asteroid.

In October, NASA successfully retrieved a sample from the asteroid Bennu, located 200 million miles from Earth. Scientists hope to use the sample and mission to better understand the beginning of the solar system.

“I did the calculation at one point and trying to go to Bennu is kind of like sending a shopping cart from New York to L.A. and hoping you can bring back a piece,” Laura Megeath, the Appold Planetarium coordinator at Lourdes University and a member of NASA’s Earth Ambassador Program, said.  

BGSU Planetarium Director Dale Smith said Bennu is of particular interest because the asteroid is a carbonaceous type, meaning that it has abundant, carbon-rich material on it.

“Carbon is the basis for life and carbon, just as water, easily boils off of something. Heat something up, and then water boils off. Carbon⁠ — same story,” Smith said. “So, if asteroids are heated very much, they will have lost their carbon, or whatever carbon they had in the beginning. But carbonaceous-type asteroids, of which Bennu is a prime example, have never been heated, so they retain whatever carbon they had at the beginning.”

Smith also noted that Bennu’s carbon samples could give insight into how some of the planets formed.

Astronomy Department Chair Dr. Andrew Layden said, “That type of asteroid is rare compared to the more rocky and metallic types of asteroids. This is potentially a look into where carbon on Earth came from in the solar system.”

NASA will use the samples to examine the properties of Bennu and compare them to other objects in space.

“In models of our early solar system we had way more than eight planets. And also, in those early models the planets that we have today weren’t necessarily in the same order,” Megeath said. “So, we can kind of get a sense of, is Bennu related to any of the planets? Was Bennu always in this same orbit? How geologically related is it to these other objects?” Megeath said.

In aNational Geographic article, Lori Glaze, director of NASA’s planetary science division, said, “Asteroids are like time capsules floating in space that can provide a fossil record for the birth of our solar system.”

Bennu’s geologic makeup is relatively unchanged, so it gives a good indication of the past.

“A place like Bennu has no weather, so the material that is there is in some respects pristine. It hasn’t changed geologically speaking for a really long time, and that’s long in terms of the geological scale or the time frame of our solar system,” Megeath said.

The landing of the OSIRIS-REx spacecraft used to retrieve the sample is referred to as Touch-And-Go, or TAG sampling.

“It was more of a grab-and-go than a full landing,” Megeath said, “They tend to measure it in a matter of seconds than minutes because it is spinning really fast. We just wanted to grab a scoop and go.”

She added, “If we stayed on too long, that gets into a whole other host of problems in terms of bringing the spacecraft back.”

Developing a method in which to obtain the sample from the asteroid was challenging. Originally NASA believed that Bennu had a sandy surface, but after orbiting, they discovered that its surface is covered by huge boulders.

“It looked like it came off of some other planet, parent body or whatever that had water,” Brenda Gift said. Gift is the Director of Student Services and Special Programs for theChallenger Learning Center in Oregon, Ohio.

NASA designed a robotic arm to retrieve the sample, but they had to make sure it was compatible with the asteroid’s rocky surface.

Gift explained how the retrieval worked. “The arm blew out nitrogen, a puff of nitrogen gas, and it created a small spot of dust and pebbles, and that’s what was collected in the container at the end of the arm,” she said.

NASA was prepared to collect two additional samples to ensure that their sample was adequate, but their original attempt was successful. On Oct. 28, they confirmed that they had closed the sample lid and taken it back into the spacecraft.

According to an article from CNN, in order to be considered an adequate sample, the arm must collect between 2 ounces and 4.4 pounds of material. This would be the largest sample of extraterrestrial material that would be brought back to Earth since the Apollo Era, the article noted.

Bennu has been undisturbed for billions of years and some mineral fragments may be older than the solar system itself.  NASA has been studying Bennu and planning a mission to extract a sample since it was first discovered in 1999 during NASA’s LINEAR Project.

The OSIRS-REx spacecraft was launched on Sept. 8, 2016 and began orbiting Bennu on Dec. 31, 2018. It spent nearly two years in this orbit state. During that time, scientists learned more about the asteroid and the sampling method.

NASA successfully collected the sample on Oct. 20, and the OSIRIS-REx will be traveling back to Earth beginning in March 2021. The spacecraft is expected to return to Earth on Sept. 24, 2023.

There have been very few missions like this because they are often difficult and expensive. One of the first asteroid landings was on asteroid 67P/Churyumov-Gerasimenko (67P/C-G) in September 2016.

“That landing was tough because we lost track of how weak the gravity is,” Smith said, “The spacecraft bounced when it went down and rebounded more times than one before it finally settled down and it was not in the intended area. And it was also out of sunlight so the solar panels could not collect energy. That spacecraft eventually died when the battery went out.”

The United States has also landed on asteroid Eros, but it was not initially planned. Later in the mission the opportunity arose, so NASA adjusted their plan and landed.

“Getting a sample returned back to the Earth is a big deal,” Smith said. “That is the importance of Bennu.”

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