Extracting Secrets from an Asteroid
When Jim Harris came into his office one day over 10 years ago, his colleagues noticed dirt under his fingernails—the reddish brown kind characteristic of the mountains outside of Denver, where he lived.
But he wasn’t doing any of the usual outdoor hobbies—gardening or even playing football with his son.
He was testing an early prototype of a device that will be used to extract a dirt sample from an asteroid—a sample that may give us the greatest clues yet into how life originated here on Earth.
Designing For New Environments
Led by the University of Arizona, NASA’s OSIRIS-REx mission aims to collect and return a sample of regolith from the surface of a small asteroid, Bennu.
Regolith refers to loose material on the surface of an object in space. Remember the famous footprint Neil Armstrong left on the moon during the Apollo 11 mission? The fluffy, upper layer of material he stepped into is regolith.
Regolith records a wealth of information on the composition of an object and the processes that have shaped the object’s evolution.
The Earth and inner planets of our solar system didn’t form immediately. It was the accumulation of lots of smaller objects that formed our planet and the other planets—and of course, out of which ultimately came all of the interesting geographies and life forms that developed here on Earth.
The very same processes that formed Earth’s surface and led to life also altered those original, source materials.
“If we want to go back and understand the building blocks of the Earth and where we came from, we can’t really find those signatures on the Earth,” said Beau Bierhaus, an OSIRIS-REx research scientist at Lockheed Martin. “We have to go into space and find small bodies that are comprised of some of the most primitive materials remaining in our solar system.”
And Bennu may have just what we are looking for.
Bennu is a carbonaceous asteroid, meaning it has carbon-bearing materials. Carbon, of course, is the basis for life on Earth.
While carbon-bearing asteroids are the most abundant kind of asteroid in the asteroid belt, very few carbon-rich meteoroids have been found on Earth—and meteorites are quickly contaminated with terrestrial materials, making the exploration of Bennu and return of pristine regolith even more interesting for scientists.
“Our mission is turning a corner in planetary exploration,” said Ed Beshore, OSIRIS-REx deputy principal investigator at the University of Arizona. “We are bringing back samples of a primitive relic of the early solar system, which will have profound scientific impact. We will be able to study these samples for many years using techniques we haven’t even thought of yet.”
Designing The TAGSAM
Given his background as a mechanical engineer, Harris knew the most obvious ideas for collecting a surface sample at Bennu, such as a scooping claw, may not work.
“The problem is that you have all of this loose material on a surface with very low gravity,” Harris said. “You can’t think of it as gravel in a driveway. As soon as you touch it, the particles may scatter.”
At the time, Lockheed Martin Space System’s chief scientist recommended Harris look into a research article he wrote back in 1989 about sample collection on comets. Drawing from the paper’s idea of using compressed gas, Harris formulated an idea of how to blow the dirt particles and capture them under the hood of a nozzle.
“Imagine a cup with air injected on one side, then holes on the other side and a filter outside of the holes,” Harris said. “We used a compressor to blow air against the ground. As the air went out through the holes and through the filter, we collected particles.”
While Harris called the early design Muucav—for vacuum spelled backwards—the final design came to be known as TAGSAM, or the Touch and Go Sample Acquisition Mechanism. The invention ultimately enabled the OSIRIS-REx mission.
In his dirt driveway in the foothills of Denver, Harris and his son tested early prototypes of the device to get a sense for just how much material can be collected using this method.
While scientists have a pretty good idea of what the material on the surface of Bennu will be like, later designs of TAGSAM have been tested on everything from popcorn to lava rock.
“We’ve tested in a thermal vacuum chamber, under both hot and cold conditions,” said Harris. “We’ve used many different types of simulants to represent the range of densities we expect. We’ve even taken it on a reduced-gravity plane for low gravity and zero-G collection testing.”
In fact, in hundreds of tests, TAGSAM has successfully collected materials, with many tests yielding more than double the amount required at the surface of Bennu.
“Rather than trying to land on the surface of Bennu and anchor ourselves in the asteroid’s microgravity environment—which is very difficult to do—we can just touch the surface using an elegant mechanism that has few moving parts and then quickly move away,” Beshore said. “This gives us a high degree of confidence that we are going to be able to pull this off.”
What We Hope To Learn
The OSIRIS-REx mission is a NASA science mission and the first to visit and return a sample from this kind of carbon-bearing asteroid. This will give us a much better understanding of what makes up these asteroids, as well as provide an inventory of building blocks for everything that is around us.
Bennu may even help us answer questions like where Earth’s water came from—whether it was delivered by an object like Bennu or perhaps from comets.
OSIRIS-REx has a suite of instruments to measure and map the asteroid, including visible-light cameras, infrared spectrometers, an X-ray spectrometer, and active-scanning LIDAR. These tools will provide incredibly detailed information about Bennu.
“We are going to have the most comprehensive, highest-spatial resolution, highest-spectral resolution data of any asteroid that we’ve ever been to,” Bierhaus said. “Beyond the sample collection, we are collecting this complementary remote sensing data set that will—in my mind—totally revolutionize our understanding of small bodies.”
Smaller objects like Bennu have much lower gravity than Earth. Gravity has played a major role in how the surface of the Earth has evolved.
When you travel to an asteroid the size of Bennu, just 500 meters in diameter, the gravity is 100,000 times less than the gravity here on Earth.
Studying Bennu’s surface, which has evolved with this small amount of gravity, gives us much greater insight into the role played by other forces. These forces can provide very interesting insights into how materials flow, move and interact in these microgravity environments—not to mention how to operate a spacecraft in such an environment.
“You just can’t recreate this environment in the lab. It’s only by going to an object like this in space where you are going to see it up close and understand how it works,” Bierhaus said. “That in turn, enhances our understanding of the sample that we get back.”
Just as lunar samples collected in the 1970s provided us with tremendous insight into the origin of the moon, the OSIRIS-REx science team is hoping to gain new insights into big questions about the solar system.
“Fundamentally, we are trying to gain a better understanding of origins—not just of Bennu but also the origins of the Earth,” said Beshore. “This is an important question because Earth is our home, and we want to understand how life began.”
As for Harris, he is confident the TAGSAM will work as designed.
“It’s a very simple design, and we’ve done an extensive amount of testing,” he said. “When you consider the full range of what the surface can be—from a rubble pile to a big rock with loose gravel on top, we’re ready.”