Seeking Solar System’s Secrets, NASA’s OSIRIS-REX Mission Touches Bennu Asteroid
October 20, 2020 | The New York Times
The spacecraft attempted to suck up rocks and dirt from the asteroid, which could aid humanity’s ability to divert one that might slam into Earth.
A NASA robot pogo-sticked off an asteroid on Tuesday and grabbed a sample of dirt and rocks, material that could give scientists new insights to the birth of the solar system.
From first impressions recorded 200 millions away on Earth, the OSIRIS-REX spacecraft pulled off its collection of bits of asteroid, a carbon-rich rock known as Bennu, perfectly. It then backed away and headed back to orbit.
“Transcendental,” Dante Lauretta, the principal investigator of the mission, said moments later. “I mean, I can’t believe we actually pulled this off.”
It will take a few more days before scientists can completely declare success. At present, they can only say that the spacecraft executed its instructions exactly as programmed. What is not yet known is how much material was actually grabbed. Scientists are hoping for at least a couple of ounces, but the sampling mechanism can hold up to four pounds.
“It’s up to Bennu now to see how the event went,” Dr. Lauretta said.
If it succeeded in its goal of sucking up some rocks and dirt from the asteroid’s surface, it could potentially unlock secrets to what the solar system was like when it first formed 4.5 billion years ago.
“The asteroids are like time capsules, floating in space, that can provide a fossil record of the birth of our solar system,” Lori Glaze, director of NASA’s planetary science division, said during a news conference on Monday.
Many asteroids — including Bennu — cross the orbit of Earth and could collide with our planet someday. A better understanding of these space rocks, which come in many types, could aid humanity’s ability to divert one that might slam into Earth.
OSIRIS-REX is a shortening of Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer.
Dr. Lauretta came up with the name. He said that as he jotted down themes of the scientific objectives — origins, spectroscopy, resources and security — he had most of the letters of Osiris, the Egyptian god who was the lord of the underworld but who also represented the seeds of regeneration to new life. He then played around with the name until he got the abbreviation he wanted.
The robotic spacecraft launched in September 2016 and arrived at Bennu in December 2018. Since then, it has been making observations of the asteroid, even documenting that it was shooting debris from its surface into space.
Shortly before noon, mission controllers at Lockheed Martin Space in Littleton, Colo., transmitted commands to the spacecraft that initiated its descent toward the asteroid. It moved at about a fifth of a mile per hour, steadily adjusting its orientation to help it safely reach the surface. It touched its extended arm against the space rock’s surface for a few seconds before backing away to a safe orbit.
On Wednesday at 5 p.m., the space agency is scheduled to hold a news conference, to be broadcast on NASA Television, to discuss how the sampling effort went and release close-up images of Bennu.
Why did NASA choose to study Bennu?
Bennu, discovered in 1999, is a carbon-rich asteroid that is almost black in color. It is about 1,600 feet wide. That compares to the Empire State Building, which is 1,454 feet tall including the antenna at the top. The carbon-rich materials are intriguing because asteroids like Bennu might have seeded Earth with the building blocks for life.
In a series of papers published in the journal Science this month, scientists reported what they have learned about Bennu so far. They found carbonate minerals in some of the asteroid’s geological features, which typically form in environments that include both hot water and carbon dioxide. That suggests that the larger body that Bennu was once part of possessed hot springs or some other sort of extensive hydrothermal system.
Scientists also noted two main types of boulders on Bennu. One is dark and rough; the other, less common, is bright and smooth. Those differences might reflect that they formed at different depths on Bennu’s parent object, and hint at its geological character.
The other reason they chose to study Bennu was the risk that it might someday collide with our planet.
Will the asteroid crash into Earth?
Bennu is categorized as a near-Earth asteroid, and scientists say there is a small chance it could slam into Earth. But even if it does, future generations will have time to prepare.
Bennu will make a series of very close passes of Earth between 2175 and 2199.
“The chance that Bennu will impact Earth is only one in 2,700,” said Andrea Riley, the program executive of an upcoming NASA mission known as the Double Asteroid Redirection Test.
If 22nd-century humans got unlucky and forgot Bennu was coming, the asteroid is not large enough to cause planet-wide extinctions. But it would be catastrophic at the point of impact.
Where did the spacecraft touch down on the asteroid?
When OSIRIS-REX arrived at Bennu, the mission’s planners were surprised at what they found.
Almost the entire surface of the asteroid is strewn with boulders, where scientists had expected to find smooth patches where the spacecraft could easily grab some samples. So the mission planners had to search long and hard for a safe enough place.
In December, they finally chose Nightingale, a spot inside a crater near Bennu’s north pole. The spacecraft, 20 feet wide and about the size of a sport utility vehicle, had to navigate carefully to the target site, which is only 26 feet in diameter. In addition, it had to avoid a wall of rocks on the eastern edge of the crater. That included a pointy pillar nicknamed Mount Doom, which is as tall as a two- or three-story building.
However, despite the risks, Nightingale offered the greatest potential scientific payoffs, with unobstructed fine-grained material that appears to contain carbon-rich minerals.
The original mission timeline set the sample attempt to occur in July. But the rigors of selecting the landing site, as well as the coronavirus outbreak, contributed to the delay to October.
How did the sample collection work?
The sampling tool — known as the Touch-and-Go Sample Acquisition Mechanism or TAGSAM — kind of looks like an automobile air filter at the end of a robotic arm.
If the operation worked as intended, when the air-filter-like sampling head touched the surface, an elbow joint in the robotic arms bent to stay in contact with Bennu’s surface for about five seconds without actually landing.
A burst of nitrogen gas then knocked up rocks and dust into the collector filter. OSIRIS-REX will then slowly back away. The goal is to collect at least a couple of ounces of material and possibly as much as 4.4 pounds.
Although Bennu turned out to be rockier than envisioned, the mission team’s analysis of the Nightingale site showed that it had a mix of small materials that the spacecraft’s sampling instrument would be able to collect.
“Thousands of particles less than two centimeters were measured in images that cover the sample site, and portions of the surface remain unresolved, suggesting even smaller particles are present,” said Beau Bierhaus, a scientist at Lockheed Martin working with the device.
It is possible that the first sampling attempt did not succeed — for example, if the sampling head unluckily sets down askew on a boulder. “We’ve known this since the beginning of the program,” Dr. Bierhaus said.
If it didn’t work on the first try, they can try again at a later date. There is enough nitrogen in the mechanism to conduct three sampling attempts if needed.
What happens after the asteroid sample is collected?
OSIRIS-REX is to leave Bennu in the middle of next year, and head back to Earth. The spacecraft will drop off a small capsule containing the rocks and dirt. The capsule will parachute to a landing in Utah on Sept. 24, 2023.
Didn’t Japan have a similar mission?
The Japanese space agency has tried to collect samples from two different asteroids during this century.
Its Hayabusa spacecraft landed on Itokawa, a near-Earth asteroid, in 2005. Although it faced a number of technical troubles over the course of its mission, it managed to return a canister to Earth in 2010 that contained less than a milligram of particles from the asteroid. Scientists have used the samples for a variety of scientific research, arguing in a study last year, for instance, that asteroids that formed closer to the sun may have been a source of Earth’s water.
But that mission was less elaborate than Japan’s follow-up spacecraft, Hayabusa2.
It met up with another asteroid, Ryugu, in 2018 and conducted months of more successful scientific observations on and around the asteroid. It dropped small robotic explorers on the asteroid, attempted a sample collection and even used an explosive device to blast a crater on its surface. It tried to collect more debris from that crater, hoping to study parts of the asteroid that haven’t been weathered by eons of time in space.
Hayabusa2 is currently traveling back to Earth, and will drop off its sample canister in Australia’s outback on Dec. 6. Japan’s space agency recently decided to extend the spacecraft’s mission, sending it to explore another target in the solar system that has not yet been selected.
What other asteroids will be visited by spacecraft from Earth soon?
NASA has three other upcoming asteroid missions.
The Double Asteroid Redirection Test mission, or DART, will be the first test of technology that could be used to divert an asteroid that is discovered to be on a collision course with Earth. Despite what is depicted in movies such as “Armageddon,” scientists generally believe blowing up an asteroid would fail if most of the smaller pieces still collide with Earth.
DART will slam into a moon orbiting a larger asteroid, and scientists will be able to measure how much the orbit of the asteroid moon changes. (There are no asteroids known to pose any danger to Earth this century, but not all asteroids have been found yet.)
Another mission, Lucy, is scheduled to launch next year. It will fly past a series of objects known as the Trojan asteroids, which are gravitationally trapped in Jupiter’s orbit.
“The Trojans, despite the fact that they’re in a very narrow region of space, are very different from one another,” said Harold F. Levison, the principal investigator of the Lucy mission. “They have different colors, different spectrum. And that probably means that they formed in very different regions of the solar system.”
The Trojans, Dr. Levison said, will most likely be remnants of the small bodies that formed the larger planets like Jupiter and Saturn. “We will revolutionize our understanding of the outer planets,” he said.
The third mission, Psyche, is a spacecraft that will visit an asteroid in the belt between Mars and Jupiter named Psyche that is about the size of Massachusetts. But more unusually, it appears to be almost entirely made of metal instead of rock.
“It holds about 1 percent of the mass of the entire asteroid belt,” said Lindy Elkins-Tanton, the principal investigator of the Psyche mission. “We’ve never visited a world made of metal.”
The spacecraft is to enter orbit around Psyche in 2026. “We’ll determine whether Psyche is part of the metal core of a broken, tiny planet from the earliest times in our solar system,” Dr. Elkins-Tanton said. “This is our best idea of what Psyche might be.”
Are other missions bringing space rocks back to Earth?
NASA astronauts and robotic Soviet probes brought lunar material back to Earth during the moon race. Scientists are still studying those samples, but there have been no fresh stocks of moon rocks and dust since the Soviet Luna 24 mission returned in 1976.
Upcoming missions by NASA and other countries could replenish samples of lunar material, and offer greater insights into more parts of the moon. The next batch could come from Chang’e 5, a Chinese mission. Some news reports suggest China could launch the mission to the moon’s Mons Rümker volcanic region in November.
While NASA is also thinking about gathering lunar material, it will work with the European Space Agency on collecting samples from Mars, too. One objective of the Perseverance rover that is on its way to Mars is to collect material from the red planet’s surface. Those materials will subsequently be handed off to a future explorer, part of the Mars Sample Return mission. Bringing the mission’s rocks and dirt to Earth will require a series of Rube Goldberg-esque interactions involving a variety of spacecraft, and is not expected to be completed until the next decade.