OSIRIS-REx overflows with asteroid samples after bagging bounty from Bennu

Captured by the spacecraft’s SamCam camera on Oct. 22, 2020, this series of three images shows that the sampler head on NASA’s OSIRIS-REx spacecraft is full of rocks and dust collected from the surface of the asteroid Bennu. They show also that some of these particles are slowly escaping the sampler head. Credit: NASA

The sampling mechanism on NASA’s OSIRIS-REx spacecraft is stuffed with specimens captured from asteroid Bennu earlier this week — so full that some of the rocks are floating out into space.

Officials said Friday they will stow the samples inside the mission’s Earth return capsule sooner than planned to minimize the loss of asteroid material.

“We had a successful sample collection attempt, almost too successful,” said Dante Lauretta, the mission’s principal investigator from the University of Arizona. “Material is escaping, and we’re expediting stow as a result of that.”

NASA’s $1 billion Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer aims to become the first U.S. spacecraft to complete a round-trip journey to an asteroid.

After a nearly two-year close-up survey of asteroid Bennu — a clump of rock measuring a third of a mile (500 meters) wide — the OSIRIS-REx spacecraft descended to the airless world Tuesday for a celestial smash and grab. Its goal was to capture at least 2.1 ounces, or 60 grams, of pebbles, rock fragments and dust particles for return to Earth.

Scientists in sophisticated terrestrial laboratories will scrutinize the asteroid samples, which might contain carbon-rich organic molecules and other minerals containing water. Both types of specimens were part of the primordial soup of ingredients that seeded life on Earth.

Data and imagery relayed to Earth from OSIRIS-REx earlier this week indicated the spacecraft performed as intended, with its Touch and Go Sample Acquisition Mechanism, or TAGSAM, robotic arm contacting the asteroid for six seconds Tuesday. A high-pressure bottle of nitrogen gas at the end of the 11-foot (3.4-meter) arm fired to force surface material from Bennu into a collection chamber, acting like a reverse vacuum cleaner.

The head at the end of the TAGSAM arm is about the size of a dinner plate. The OSIRIS-REx spacecraft and its sampling system were designed and built by Lockheed Martin.

OSIRIS-REx pulsed thrusters to take off from the asteroid after six seconds, officials said.

Lauretta said Friday he is “highly confident” the sample collection attempt was successful, and that it collected “abundant mass, definitely evidence of hundreds of grams of material, and possibly more.”

“My big concern now is that the particles are escaping because we’re almost a victim of our own success here,” Lauretta said Friday afternoon in a conference call with reporters.

Ground teams got their first glimpse of the sample collection device with a series of images downlinked by the spacecraft Thursday. OSIRIS-REx moved the robotic arm into position for a close-up view by the mission’s sample camera, or SamCam.

“We looked at the sample head, and it’s full of sample material, much more than 60 grams,” said Thomas Zurbuchen, associate administrator for NASA’s science mission directorate.

“There is so much in there that the diaphragm that was supposed to keep the sample in is stuck open, and we’ve observed some of the sample pieces escaping into space,” Zurbuchen said. “Therefore, now time is of the essence.”

Lauretta said the images showed around five rocks lodged in the opening of the sample collection chamber. The particles are right at the size limit to enter the sampling mechanism, and they appear to have wedged open a mylar flap, which acts as a lid on the sample head.

The movement of the TAGSAM arm Thursday likely contributed to the loss of some of the samples observed in the images beamed back to Earth. Lauretta estimated that 5 to 10 grams of “flaky” material could have been lost from the TAGSAM head Thursday “in a worst-case estimate” as the samples were disturbed by the arm’s movements.

With the robot arm motionless, managers have seen less evidence of a particle cloud around the spacecraft in images from OSIRIS-REx’s star tracker navigation camera.

Mission managers originally scheduled a sample mass measurement Saturday, during which OSIRIS-REx would extend its sampling arm as it entered a spin to measure the spacecraft’s moment of inertia. Ground teams planned to compare the data to a similar maneuver performed before OSIRIS-REx collected its sample from Bennu to estimate the mass of fresh asteroid material inside the TAGSAM head.

If the estimate indicated OSIRIS-REx had captured more than 60 grams of asteroid samples, plans called for stowage of the specimens inside the return carrier in early November. If not, there was an opportunity for OSIRIS-REx to try another sample collection run on Bennu in January.

With the images downlinked Thursday, officials are now sure the spacecraft grabbed enough of a sample to meet the mission’s minimum success criteria.

“I made the decision to forego the sample mass measurement, and asked the team to prepare immediately to do the analysis to see whether we’re ready for stow,” Zurbuchen said.

NASA announced the Friday afternoon press briefing less than hour ahead of time. Thomas Zurbuchen, head of NASA’s science mission directorate, apologized for the late notice.

“I’m sure you were planning something else tonight,” Zurbuchen said. “I doubt though that it would be more exciting than what we’re going to talk about here.”

The next step for OSIRIS-REx will be to place the sampling mechanism inside a return capsule mounted on the spacecraft. The 31-inch (0.8-meter) diameter sample return capsule is designed to protect the asteroid sample during re-entry into Earth’s atmosphere Sept. 24, 2023.

“We all have one goal, and that is to bring the maximum sample back to Earth,” Zurbuchen said.

“We do not believe that there is anything we can do with the system that we have to go fix the diaphragm,” Zurbuchen said. “So the variables that we can control are: No. 1, how much we rattle this thing around, so we’ve minimized that with the actions that we’ve taken already, and No. 2, is to shorten the time to get this stowed, at which point the particles are locked into the capsule that will bring them back to Earth.”

Over the weekend, engineers at Lockheed Martin’s control facility near Denver will validate the stow procedure, which did not originally account for the possibility that rock fragments and dust and particles might be leaking out of the sampling mechanism.

Zurbuchen said NASA will also reserve time dedicated to OSIRIS-REx on the agency’s Deep Space Network, a group of large tracking and communication antennas at sites in California, Australia, and Spain. He said engineers at the space network will prioritize OSIRIS-REx’s “contingency operations” to ensure the mission gets continuous communications coverage as ground teams command the delicate sample stow procedure.

On Monday, spacecraft operators near Denver will check out a camera looking at OSIRIS-REx’s sample return capsule to monitor the stow operation. If all goes according to plan, mission control could begin placing the asteroid specimens inside the return carrier as soon as Tuesday, Lauretta said.

The ground team will uplink commands for OSIRIS-REx to stow its sample in a series of steps, allowing engineers to regularly pause and assess the situation. Lauretta said the motion involved with the stow operation will likely cause more particles to leak out of the sampling system, and managers want to make sure the material doesn’t interfere with any mechanical interfaces or damage the return capsule.

It will all play out more than 200 million miles (320 million kilometers) from Earth, with a communications delay of more than 18 minutes.

“We can command the arm to move … acquire an image, download that image, analyze it, and then make a decision,” Lauretta said. “Did we see a particle that looks like a mechanical interference? And then what do we want to do to mitigate that as we move forward? So it’ll be very slow and deliberate and play out over several days of activity.”

Officials hope the specimens could safely be sealed inside the sample return capsule by the end of next week.

After the opening the sample return carrier’s lid, ground teams will send commands for the robotic arm to place the TAGSAM head onto a capture ring inside the capsule. Then it will activate a “tube cutter” to cut lines leading from the device’s nitrogen gas bottles, and fire a separation bolt to sever the TAGSAM head from the robotic arm.

“So that is a one-way ticket, and then we move the arm away and the entire head remains inside that capture ring mechanism,” Lauretta. “And then we’ll pull the sample return capsule (lid) down. There are several latches. Only one latch is required for Earth entry.”

Lauretta said he is confident the sample return capsule can seal itself despite the risk of obstructions from floating asteroid particles.

“Once the sample head is safely stowed in the return capsule, it’s closed, it’s protected, and there will no more mass loss,” he said.

The images of the overflowing sampling mechanism Thursday also prompted officials to cancel a thruster firing Friday to slow OSIRIS-REx’s speed away from Bennu. The burn would have preserved the option for a second touch and go sampling run at Bennu.

“We will not be returning to the asteroid,” Lauretta said. “So we said our goodbye, I believe, to Bennu on Tuesday, and we’re solely focused on stowing the sample safely, and then once that’s done, on preparing for return cruise and Earth return.”

With the decision to skip the sample mass measurement, scientists won’t know exactly how much of Bennu they got until OSIRIS-REx brings the samples back to Earth.

“We were looking forward to the sample mass measurement and the certainty that gave us in terms of planning out the sample analysis activities,” Lauretta said. “But the good news is we see a lot of material.”

OSIRIS-REx will depart the vicinity of Bennu in early March to begin the journey back to Earth. The spacecraft will release the sample return capsule as it approaches Earth, targeting a parachute-assisted landing at the Utah Test and Training Range while the OSIRIS-REx mothership diverts and heads again into the solar system.

Scientists will recover the capsule and transport it to NASA’s Johnson Space Center in Houston, where they will begin analysis of the Bennu specimens inside a pristine astromaterials lab, the same facility that houses lunar rocks returned by the Apollo astronauts.

OSIRIS-REx will bring home the biggest haul of asteroid material ever, but it’s not the only mission with sights on returning samples from an asteroid.

Japan’s Hayabusa 2 spacecraft is on course to release a sample carrier to land in Australia on Dec. 6 with a much smaller load of asteroid material than OSIRIS-REx.

NASA and the Japan Aerospace Exploration Agency have agreed to share a small percentage of the OSIRIS-REx and Hayabusa 2 samples between U.S. and Japanese scientists.

NASA’s OSIRIS-REx spacecraft’s navigation camera captured this image of asteroid Bennu in 2019 from a distance of approximately 1 mile (1.6 kilometers). The large boulder in partial shadow at the lower right of the frame is about 165 feet (50 meters) across. Credit: NASA/Goddard/University of Arizona/Lockheed Martin

While the mission’s scientific payoff won’t come for another three years, the OSIRIS-REx team is already digging into new data about the surface properties of Bennu. Scientists believe the inside of the asteroid is porous, and the boulders on its surface are low-strength and easily crushable.

An initial assessment of the spacecraft’s motion during the touch and go landing Tuesday suggests OSIRIS-REx’s sampling arm pressed about 2 inches, or 5 centimeters, into the loose dust on Bennu’s surface before firing its nitrogen gas bottle.

“The contact was sensed by the accelerometers on-board the spacecraft,” Lauretta said.

A pogo spring on the robotic arm “did not deflect noticeably at all,” Lauretta said, and the sampling mechanism continued moving into the asteroid’s gravelly surface, reaching a depth of up to 19 inches, or 48 centimeters, before OSIRIS-REx activated its back-away thrusters to take off again.

Then it took another three seconds for the spacecraft’s rocket thrusters put OSIRIS-REx in reverse.

“It took the thrusters an additional three seconds to stop that forward motion, and then begin accelerating backwards, ultimately achieving that 40 centimeter per second (0.9 mph) escape velocity,” Lauretta said. “So that’s a wealth of information that will be provided. It tells us an enormous amount about the material properties of the regolith at the contact point.”

Testing of the OSIRIS-REx sampling system before launch showed that the device was able to scoop up the most rocks and dust when it was able to burrow itself into asteroid-like material.

“I remember early on in development, it was a real question,” Lauretta said. “The mechanical properties of the surface of the asteroid was probably the largest unknown in the mission design. So we had to design, everything from a completely rigid surface like running into a slab of concrete down to what we called the ‘fairy castle’ structure with almost no resistance.

“And that was part of the challenge of the mission was coming up with a design that would operate under all of those different circumstances, maintaining spacecraft safety primarily. We’re definitely on the much softer end of that spectrum. We are seeing that the regolith behaves very much like a granular medium, and it flowed away from the TAGSAM head as we pushed through, and the science team is absolutely ecstatic about the dataset we collected.”

Quelle: SN


A NASA Probe Is So Full of Asteroid Material That It Now Has A Problem

A NASA spacecraft sent out to collect a sample of rock and dust from an asteroid has nabbed so much that it's created an unexpected problem.

Rocks are jammed in the device in a way that's keeping a Mylar flap open, creating a gap that's letting some of the collected pebbles and dust drift out into space.

"We had a successful sample collection attempt — almost too successful. Material is escaping," says Dante Lauretta of the University of Arizona, the principal investigator for the OSIRIS-REx mission. "We think we're losing a small fraction of material, but it's more than I'm comfortable with. I was pretty concerned when I saw these images coming in."

To prevent any further loss, the team is now preparing to stow the sample collection device quickly into its return capsule, possibly starting the stowing process as soon as Tuesday. The capsule is expected to return to Earth in 2023.

Researchers believe they collected hundreds of grams of material, but they won't know for sure until the capsule returns to Earth.

They had been planning a maneuver that would spin the spacecraft and let them make a precise determination of how much rock and dusty material they'd gotten. The thinking was that if they hadn't managed to collect much, they might have another go at touching the asteroid in January and getting some more.

But they called off the spacecraft-spinning trick when they realized that the collector is so full that material is jamming it open and that stuff is being lost.

That's because they want to minimize the spacecraft's movement until the rock and dust sample is safely sealed up in the return capsule. "It would risk loss of material," Lauretta says. "We have enough evidence of successful sample collection."

Nothing like this problem was ever seen in simulations of the mission that the team did on Earth, he says. It's now looking like the collection device must have penetrated farther down into the asteroid's surface than expected — perhaps as deep as 48 centimeters, or about a foot and a half.

"I basically directed the team to put as minimal activity on the spacecraft as necessary and start focusing on the early stow of sample," Lauretta says. "It's very exciting, very surprising, but overall, excellent news."

Quelle: NPR
Update: 27.10.2020

NASA’s OSIRIS-REx Spacecraft Goes for Early Stow of Asteroid Sample


This illustration shows NASA’s OSIRIS-REx spacecraft stowing the sample it collected from asteroid Bennu on Oct. 20, 2020. The spacecraft will use its Touch-And-Go Sample Acquisition Mechanism (TAGSAM) arm to place the TAGSAM collector head into the Sample Return Capsule (SRC).
Credits: NASA/University of Arizona, Tucson

NASA’s OSIRIS-REx mission is ready to perform an early stow on Tuesday, Oct. 27, of the large sample it collected last week from the surface of the asteroid Bennu to protect and return as much of the sample as possible.


On Oct. 22, the OSIRIS-REx mission team received images that showed the spacecraft’s collector head overflowing with material collected from Bennu’s surface – well over the two-ounce (60-gram) mission requirement – and that some of these particles appeared to be slowly escaping from the collection head, called the Touch-And-Go Sample Acquisition Mechanism (TAGSAM).


A mylar flap on the TAGSAM allows material to easily enter the collector head, and should seal shut once the particles pass through. However, larger rocks that didn’t fully pass through the flap into the TAGSAM appear to have wedged this flap open, allowing bits of the sample to leak out.


Because the first sample collection event was so successful, NASA’s Science Mission Directorate has given the mission team the go-ahead to expedite sample stowage, originally scheduled for Nov. 2, in the spacecraft’s Sample Return Capsule (SRC) to minimize further sample loss.


"The abundance of material we collected from Bennu made it possible to expedite our decision to stow,” said Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona, Tucson. “The team is now working around the clock to accelerate the stowage timeline, so that we can protect as much of this material as possible for return to Earth."


Unlike other spacecraft operations where OSIRIS-REx autonomously runs through an entire sequence, stowing the sample is done in stages and requires the team’s oversight and input. The team will send the preliminary commands to the spacecraft to start the stow sequence and, once OSIRIS-REx completes each step in sequence, the spacecraft sends telemetry and images back to the team on Earth and waits for the team’s confirmation to proceed with the next step.


Signals currently take just over 18.5 minutes to travel between Earth and the spacecraft one-way, so each step of the sequence factors in about 37 minutes of communications transit time. Throughout the process, the mission team will continually assess the TAGSAM’s wrist alignment to ensure the collector head is properly placed in the SRC. A new imaging sequence also has been added to the process to observe the material escaping from the collector head and verify that no particles hinder the stowage process. The mission anticipates the entire stowage process will take multiple days, at the end of which the sample will be safely sealed in the SRC for the spacecraft’s journey back to Earth.


“I’m proud of the OSIRIS-REx team’s amazing work and success to this point,” said NASA’s Associate Administrator for Science Thomas Zurbuchen. “This mission is well positioned to return a historic and substantial sample of an asteroid to Earth, and they’ve been doing all the right things, on an expedited timetable, to protect that precious cargo.”


NASA’s Goddard Space Flight Center in Greenbelt, Maryland, provides overall mission management, systems engineering and the safety and mission assurance for OSIRIS-REx. The University of Arizona, Tucson leads the mission’s science observation planning and data processing. Lockheed Martin Space in Denver built the spacecraft and is providing flight operations. Goddard and KinetX Aerospace, in Tempe, Arizona, are responsible for navigating the OSIRIS-REx spacecraft. OSIRIS-REx is the third mission in NASA’s New Frontiers Program, which is managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington.

Quelle: NASA


Update: 28.10.2020


NASA's OSIRIS-REx spacecraft is tucking away precious asteroid samples for safekeeping

Captured by the OSIRIS-REx spacecraft’s SamCam camera on Oct. 22, 2020, this series of three images shows that the sampler head on the NASA spacecraft is full of rocks and dust collected from the surface of the asteroid Bennu. Some of these particles are slowly escaping the sampler head. Analysis by the OSIRIS-REx team suggests that bits of material are passing through small gaps where the head’s Mylar flap is slightly wedged open.

Captured by the OSIRIS-REx spacecraft’s SamCam camera on Oct. 22, 2020, this series of three images shows that the sampler head on the NASA spacecraft is full of rocks and dust collected from the surface of the asteroid Bennu. Some of these particles are slowly escaping the sampler head. Analysis by the OSIRIS-REx team suggests that bits of material are passing through small gaps where the head’s Mylar flap is slightly wedged open.
(Image: © NASA)

NASA's asteroid-sampling maneuver last week was so successful that the spacecraft will begin stowing its new souvenirs today (Oct. 27) to avoid losing rock by idling around.


The agency's OSIRIS-REx spacecraft touched down on an asteroid named Bennu on Oct. 20 and puffed nitrogen gas at the space rock to blow pieces into the arm's sampling head before backing away to safety. When OSIRIS-REx scientists were able to see images of the sampling head on Oct. 22, they realized that the maneuver had been so successful that asteroid rubble blocked the flap designed to close off the material in the arm.

Some of the spacecraft's precious haul started leaking away.

So, in a procedure that's become familiar for the OSIRIS-REx team, the mission's scientists and engineers reevaluated their plans. Originally, the spacecraft was scheduled to make a careful pirouette over the weekend that would tell scientists precisely how much weight OSIRIS-REx had picked up in its encounter. But without the flap fully closed, that spin would result in the spacecraft losing more space rock.


To prevent this, the mission staff decided to skip that step and instead go ahead and stow the sample, a days-long maneuver that starts today, rather than waiting until Nov. 2 as had been previously planned. The process will tuck the spacecraft's sampling head securely into its sample return capsule for safe travel to Earth. 


n artist's depiction of the OSIRIS-REx spacecraft stowing its sampling head.  (Image credit: NASA/University of Arizona, Tucson)

The OSIRIS-REx (short for Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) mission isn't done studying Bennu, however. The mission is scheduled to remain at the space rock until the middle of next year before turning back to Earth, where it will deliver its cargo in 2023.

Quelle: SC


Update: 29.10.2020


OSIRIS-REx In the Midst of Sample Stowage


Yesterday, NASA’s OSIRIS-REx mission successfully placed the spacecraft’s sample collector head into its Sample Return Capsule (SRC). The first image shows the collector head hovering over the SRC after the Touch-And-Go Sample Acquisition Mechanism (TAGSAM) arm moved it into the proper position for capture. The second image shows the collector head secured onto the capture ring in the SRC. Both images were captured by the StowCam camera.


Today, after the head was seated into the SRC’s capture ring, the spacecraft performed a “backout check,” which commanded the TAGSAM arm to back out of the capsule. This maneuver is designed to tug on the collector head and ensure that the latches – which keep the collector head in place – are well secured. Following the test, the mission team received telemetry confirming that the head is properly secured in the SRC.


Before the sampler head can be sealed into the SRC, two mechanical parts on the TAGSAM arm must first be disconnected – these are the tube that carried the nitrogen gas to the TAGSAM head during sample collection and the TAGSAM arm itself. Over the next several hours, the mission team will command the spacecraft to cut the tube and separate the collector head from the TAGSAM arm. Once the team confirms these activities have executed as planned, they will command the spacecraft to seal the SRC.


StowCam, a color imager, is one of three cameras comprising TAGCAMS (the Touch-and-Go Camera System), which is part of OSIRIS-REx’s guidance, navigation, and control system. TAGCAMS was designed, built and tested by Malin Space Science Systems; Lockheed Martin integrated TAGCAMS to the OSIRIS-REx spacecraft and operates TAGCAMS.

Quelle: NASA


Update: 1.11.2020


NASA stops asteroid sample leaks from 205 million miles away

This Dec. 2, 2018 photo from NASA’s OSIRIS-REx spacecraft, obtained March 18, 2019 courtesy of NASA/Goddard/University of Arizona, shows a mosaic image of asteroid Bennu, composed of 12 PolyCam images, from a distance of 12 miles.

Dec. 2, 2018 photo from NASA’s OSIRIS-REx spacecraft, obtained March 18, 2019 courtesy of NASA/Goddard/University of Arizona, shows a mosaic image of asteroid Bennu, composed of 12 PolyCam images, from a distance of 12 miles.

In this image taken from video released by NASA, the OSIRIS-REx spacecraft takes a sample of the surface of asteroid Bennu on Tuesday, Oct. 20, 2020. (NASA via AP)
In this image taken from video released by NASA, the OSIRIS-REx spacecraft takes a sample of the surface of asteroid Bennu on Tuesday, Oct. 20, 2020. (NASA via AP)

The OSIRIS-REx spacecraft has secured its samples from asteroid Bennu, moving one step closer to becoming the first NASA mission to return rocks and dust from an asteroid.

On Oct. 20, the spacecraft spent six seconds on the surface of Bennu. It fired a nitrogen gas bottle and collected the rocks and dust that were kicked up by the gas.

On NASA’s OSIRIS-REx samples asteroid that could have secrets of origins of life on Earth 

NASA’s goal was to collect at least 60 grams of material, which is roughly equivalent to a full-size candy bar. The spacecraft is believed to have been completely full of samples — 2,000 grams, which is more than 4 pounds — immediately after touching the asteroid’s surface.

But the container’s lid was propped slightly open by larger rocks, and tens of grams of material are believed to have been lost to space.

This prompted the OSIRIS-REx team to accelerate the securing of its samples.

They did this over 36 hours, sending commands to the spacecraft with a one-way time delay of 18.5 minutes (Bennu is more than 205 million miles from Earth), and safely tucked the samples inside the spacecraft’s Sample Return Capsule. This capsule has a heat shield and parachutes and is the only portion of the spacecraft that will reenter Earth’s atmosphere in September 2023. 

No more material can escape now that the samples are inside the capsule. Using a camera, scientists could see 17 percent of the collection volume and estimated that 400 grams are in that visible portion.

“I believe we still have hundreds of grams of material in the sample collector head,” Dante Lauretta, the OSIRIS-REx principal investigator at the University of Arizona, said Thursday during a news conference. “Probably over a kilogram, easily.”

The spacecraft will orbit Bennu until its departure window opens in March. That’s when the asteroid will be aligned with Earth for a fuel-efficient return flight.

On NASA’s Johnson Space Center in Houston is preparing to receive these samples 

Bennu, formed nearly 4.5 billion years ago, is like a time capsule for the solar system’s earliest years. Scientists hope the samples can help answer questions about the origin of life on Earth.

And because Bennu has a 1-in-2,700 chance of colliding with the Earth between the years 2175 and 2199, knowing more about its composition could also help future generations create a deterrence plan should it be needed.

Quelle: Houston Chronicle


Update: 12.11.2020




Last week NASA snagged a sample from the surface of asteroid Bennu, an Empire State Building-sized body that Southwest Research Institute scientists have helped map with nearly unprecedented precision. Using orbital data from the OSIRIS-REx spacecraft, researchers measured centimeter- to meter-sized craters on the boulders scattered around its rugged surface to shed light on the age of the asteroid.

While the collected sample will yield enormous scientific value when it is returned to Earth in 2023, a key job for scientists during the time in orbit at Bennu was to understand the geology of the entire asteroid to provide important context for the sample. This provides insights into all the processes that might have affected the nature of the sample.

“The amazing data collected by OSIRIS-REx at asteroid Bennu have allowed us to not just find impact craters across its surface, but to actually find and study the craters on the surfaces of boulders,” said SwRI’s Dr. Kevin Walsh, a coauthor of “Bennu’s near-Earth lifetime of 1.75 million years inferred from craters on its boulders,” published October 26 in the journal Nature. “The craters that we could observe and measure on the surfaces of boulders allowed us to estimate their strengths, a first-of-its-kind measurement.”

Bennu is a dark rubble pile held together by gravity and thought to be an asteroid remnant created following a collision involving a larger main-belt object. Boulders are scattered across its heavily cratered surface, indicating that it has had a rough-and-tumble life since being liberated from its much larger parent asteroid millions or even billions of years ago. Scientists use studies of impact craters to determine the ages of planetary surfaces.

Team members from the University of Arizona developed a mathematical formula that allows researchers to calculate the maximum impact energy a boulder of a given size and strength could endure before being smashed.

Walsh, lead author Dr. Ron Ballouz (a postdoctoral fellow at the University of Arizona), and colleagues brought together an understanding of the number of craters, the strength of the materials impacted, and the numbers of impactors to help constrain the chronology of Bennu’s existence in the inner Solar System at 1.75 million years. Since the spacecraft arrived at Bennu in 2018, scientists have been characterizing the asteroid’s composition from orbit and comparing it to other asteroids and meteorites. Now NASA has collected an actual sample of its surface that scientists will be able to study.

“We held our breath as the spacecraft touched the asteroid’s boulder-strewn surface with a robotic arm for a few seconds to collect a sample of rocks and dust on October 20 — a first for NASA,” Walsh said. “Hitting pay dirt on the first attempt is fantastic. We look forward to learning so much more when the sample arrives back at Earth in 2023.”

The manuscript describes a method for measuring the strength of solid objects uses remote observations of craters on surface boulders. Determining the strengths of boulders on asteroid surfaces is a leap forward from measuring the strength of much smaller meteorites, which have the bias of surviving passage through Earth’s atmosphere.

“The rocks tell their history through the craters they accumulated over time,” said Ballouz. “The boulders serve as witnesses to Bennu’s time as a near-Earth asteroid, validating decades of dynamical studies of the lifetime of near-Earth asteroids.”

Quelle:  Southwest Research Institute

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