On the morning of September 24, a space capsule containing a pristine sample of the near-Earth asteroid Bennu will enter Earth’s atmosphere wreathed in fire. During a 13-minute descent, the craft will use its heat shield to dissipate speed through friction. If all goes well, it will safely touch down on a military range in Utah, marking the end of NASA’s seven-year-long Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer—the OSIRIS-REx mission.
For more than half a decade, the members of this mission faced multiple technical challenges: building, testing, and launching the OSIRIS-REx spacecraft in 2016; rendezvousing with asteroid Bennu in 2018 about 207 million miles from Earth; using a robotic arm to grab half a cup’s worth of Bennu in 2020; and setting a course back to Earth in 2021.
But the scope of the OSIRIS-ReX mission stretches from the distant past into the relatively closer future. Nearly two decades ago, astronomers set out to not only get up close and personal with an ancient asteroid, but actually bring some home. And its scientific observations dip billions of years into the past. Samples from this more than 4.5 billion-year-old asteroid are likely to provide clues to the origin of life itself. It will also help prepare us for a moment, centuries from now, when Bennu could threaten to strike Earth.
The power of a pristine asteroid
The OSIRIS-REx sample is a chance to thoroughly examine what compounds may have been present in the early solar system. By bringing bits of the space rock to Earth, researchers can use the most powerful laboratory techniques available—not just what tools can fit on a spacecraft.
”It’s tremendously powerful to be able to get something back in the laboratory,” says Jason Dworkin is a biochemist and astrobiologist at NASA’s Goddard Space Flight Center. He’s been the project scientist for OSIRIS-REx since NASA accepted the mission proposal in 2011, and has been involved in the mission’s planning since its conception in 2004. “You can change your mind about what you’re looking for. As new discoveries come in, you can adjust your instrumentation. You can have devices that are not only too large to get on the spacecraft, but for us, even larger than the launch pad.”
[Related: The asteroid that created Earth’s largest crater may have been way bigger than we thought]
Dworkin has long been interested in the ways interstellar chemistry can shed light on how the early Earth’s organic compounds combined to form life as we know it. It’s possible that material from asteroids, made of similar stuff as Bennu, helped deliver some necessary ingredients when they struck our planet.
We know the strikes happened, Dworkin says, but we don’t know how relevant the “asteroidal input” from objects like Bennu was.
Rapidly recovering the sample
Before scientists like Dworkin can probe the bits of rock for data, they have to get the samples safely into the lab. Sample collection teams—NASA experts and academic mission scientists, US military representatives, and scientists and engineers from Lockheed Martin, which built the OSIRIS-REx spacecraft—have spent the summer practicing to recover the Bennu sample as quickly as possible.
As the capsule nears Earth’s atmosphere, the recovery teams will board helicopters, using infrared imaging to track the capsule as it descends. Their goal is to swiftly arrive to where the capsule comes to rest, which will be within a 36-mile by 8.5-mile area of the Department of Defense’s Utah Test and Training Range near Salt Lake City. The reason for the haste is to limit the chances that anything Earthly would contaminate the 8.8 ounces of pristine Bennu material.
A training model of the OSIRIS-REx sample return capsule falls during a drop test in August. NASA/Keegan Barber
To further guard against this, the team recovering the capsule will also take samples of soil and material from around the landing site. That way, if scientists detect something “extraordinary,” Dworkin says, “we can make sure that it cannot be explained by contamination or by something else from the environment.”
Once collected, the capsule will be taken to a temporary clean room at the military range. There, it will be disassembled and packaged for a flight to NASA’s Johnson Space Center in Houston, where the space agency has built a specialized clean room environment. This will be Bennu’s home on Earth.
“The sample comes back and is studied by the science team for two years,” Dworkin says. “Within six months, we produce a catalog of what we’ve observed based on how to describe the sample without damaging the sample using non-invasive techniques.”
What an asteroid on Earth can tell us
The science team has 12 major hypotheses and 54 sub-hypotheses to test, according to Dworkin, which fall into four broad categories.
The first category is testing the observations that OSIRIS-REx made of Bennu while in space. NASA wants to know: If the results of remote instrument measurements of, say, the asteroid’s mineralogy hold up when tested on the ground? If so, this will be a baseline for additional remote studies of other asteroids NASA won’t send a spacecraft to sample.
The second category, Dworkin’s favorite, is examining what organic compounds might exist in the sample. It may contain amino acids, sugars, and aldehydes. These are potentially some of the same ingredients that were present on Earth when life began. Studying how they exist on Bennu can reveal the chemical changes they’ve undergone over the eons in space.
The history of the solar system is the third category. This is the tale, told by the sample, of our solar neighborhood: all the way “from the protosolar nebula to the formation of the crater out of which we collected the sample,” Dworkin says. In this view, as Bennu traveled in the frigid space, it was as if material from the solar system’s early days was held in cold storage.
[Related: Local asteroid Bennu used to be filled with tiny rivers]
And the fourth category of study will be analyzing if and how bringing a piece of Bennu home changes the sample. ”We saw images of it before we stowed it; is that the same, or did it change on the reentry into Earth’s atmosphere?” Dworkin says. “Do we have evidence of contamination from the spacecraft, from the sample processing and handling?
Some of the answers to questions across all four categories could come within months to a few years. But NASA is preparing for the long haul. Today’s scientists will only have immediate access to about a quarter of the sample. The rest will be held in cold storage for decades, on the assumption that later generations will have better tools and more knowledge to bring to bear.
NASA wants to avoid repeating mistakes the agency made with some of the Apollo-era moon samples, when tests weren’t as conservative with lunar material. “ “That’s arming the future, and making sure that future generations thank us instead of curse us,” Dworkin says.
There’s one final forward-looking aspect to the OSIRIS-REx mission. In the late 22nd century, sometime between 2170 and 2200, Bennu has a slim chance of hitting Earth. It’s “a small percentage, but not nothing,” Dworkin notes. Information gathered by OSIRIS-REx and subsequent sample studies could help scientists and political leaders decide, with decades of preparation, whether they need to take action to deflect Bennu to prevent a disastrous impact.
”That’s a wonderful feeling to be able to work on a mission for so long, and have it pay off scientifically for the future, and perhaps planetary defense for the future,” Dworkin says. ”That happens when you start thinking about what happened four and a half billion years ago. You start thinking about the future too.”
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