Tag Archives: #bennu

New Impact Probability Calculation For Bennu (Planetary Science)

“We have never modeled the trajectory of an asteroid with this precision before,” explains Davide Farnocchia of NASA, the first author of a new study that recalculated the orbits of the asteroid Bennu with the data obtained from the Osiris-Rex spacecraft. the next two centuries. Until 2135 we can rest assured; after that, he has some small chance of going through the wrong gravity gate

On September 24, 2023, an abundant handful of carbonaceous regolith is expected to arrive on earth that the NASA Osiris-Rex spacecraft collected in October 2020 directly from the surface of the asteroid Bennu . Also on September 24, but many years later, precisely in 2182, the Earth risks being delivered home to the entire mass of the asteroid from half a kilometer in diameter. Let’s see why.

The asteroid (101955) Bennu , discovered in 1999 and repeatedly observed with optical telescopes and radar, is a Near-Earth Object potentially at risk of intersecting its orbit with Earth’s. Indeed, in the Palermo scale – used by astronomers to assess the risk of impact – it is one of the two objects with the highest overall probability of causing damage to the Earth .

new study , published in the journal Icarus , has now considerably refined the predictions on a possible encounter between Bennu and our planet, based on the information gathered by the Osiris-Rex mission in the more than two years in which he visited Bennu. Osiris-Rex has closely investigated the size, shape and composition of the asteroid, studying its rotation and orbital trajectory in much more detail than any Earth-based telescope could. This has now made it possible to more accurately estimate its path over the next couple of centuries .

The new study determined an overall probability of impact by the year 2300 of 1 in 1750 (or 0.057 percent), while – as mentioned – September 24, 2182 would be the single most significant date in terms of potential, with a probability of impact of 1 in 2700 (or about 0.037 percent).

“The Osiris-Rex data give us much more precise information, we can test the limits of our models and calculate Bennu’s future trajectory with a very high degree of certainty up to 2135”, comments the first author of the study Davide Farnocchia , of the Center for Near Earth Object Studies ( Cneos ) by NASA. “We have never modeled the trajectory of an asteroid with this precision before.”

Illustration of the “gravitational keyholes” that Bennu could get into in 2135. Credits: Nasa / Goddard

In 2135, the asteroid Bennu will get very close to Earth. While not posing any risk at that time , it is essential for scientists to be able to understand as accurately as possible how Earth’s gravity will alter the asteroid’s path around the Sun. In particular, if the space body will travel some specific , passing trajectories . through certain points called ” holes of gravity lock ” ( gravitational keyhole ), which would put it on a collision course with Earth during future orbit.

To calculate exactly where Bennu will be during his close passage of 2135 and whether or not he can pass through a gravitational keyhole , Farnocchia and his team evaluated various types of forces that, however small, can affect the path of the asteroid while orbiting the Sun.

Among these forces, the heat of the Sun itself plays a crucial role thanks to a phenomenon called the Yarkovsky effect , which, with the rotation of the body between “day” and “night”, causes the energy absorbed by the Sun to be dispersed into space, generating a small amount of thrust on the asteroid. With the forthcoming availability of a sample of the Bennu surface, the thermal properties of the asteroid can be determined even more accurately .

“The Yarkovsky effect acts on asteroids of all sizes and, although it was measured for a small fraction of the asteroid population from afar, Osiris-Rex gave us the first opportunity to measure it in detail as Bennu traveled around the Sun”, explains Steve Chesley of Jpl Nasa, one of the authors of the new study. “The effect on Bennu is equivalent to the weight of three grapes constantly acting on the asteroid: tiny, yes, but significant when determining the future possibilities of Bennu impact in the decades and centuries to come.”

Sampling maneuver on Bennu performed by Osiris-Rex. Credits: NASA / Goddard / University of Arizona

The research team also considered many other perturbing forces , including the gravity of the Sun, planets, their moons and more than 300 other asteroids, resistance caused by interplanetary dust, solar wind pressure, and ejection events from particles from Bennu himself.

The researchers also evaluated the force exerted by Osiris-Rex during the performance of its Touch-And-Go sample collection event on October 20, 2020, to see if it could slightly alter Bennu’s orbit. Theoretical estimates were confirmed, according to which the small touch of the sampler would have a negligible effect .

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Featured image: The asteroid Bennu in a mosaic of images taken by the Nasa Osiris-Rex probe. Credits: NASA / Goddard / University of Arizona


Provided by INAF

SwRI Scientist Studies Tiny Craters On Bennu Boulders to Understand Asteroid’s Age (Planetary Science)

Scientists inferred Bennu’s sojourn in the inner Solar System at 1.75 million years.

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.

SwRI and the University of Arizona studied centimeter- to meter-sized craters on boulders scattered around the surface of the near-Earth asteroid Bennu. This composite shows the cascading rim of an ancient crater from the time Bennu resided in the asteroid belt. The overlaid colors highlight the topography of the boulder with warmer colors indicating higher elevations. ©University of Arizona/Johns Hopkins APL/York University.

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.”

Provided by Southwest Research Institute

Asteroid’s Scars Tell Stories Of Its Past (Planetary Science)

Impact craters left by space debris in the boulders on asteroid Bennu’s rugged surface allowed researchers to reconstruct the history of the near-Earth object in unprecedented detail.

By studying impact marks on the surface of asteroid Bennu – the target of NASA’s OSIRIS-REx mission – a team of researchers led by the University of Arizona has uncovered the asteroid’s past and revealed that despite forming hundreds of millions of years ago, Bennu wandered into Earth’s neighborhood only very recently.

This image shows four views of asteroid Bennu along with a corresponding global mosaic. The images were taken on Dec. 2, 2018, by the OSIRIS-REx spacecraft’s PolyCam camera, which is part of the OCAMS instrument suite designed by UArizona scientists and engineers. ©NASA/Goddard/University of Arizona.

The study, published in the journal Nature, provides a new benchmark for understanding the evolution of asteroids, offers insights into a poorly understood population of space debris hazardous to spacecraft, and enhances scientists’ understanding of the solar system.

The researchers used images and laser-based measurements taken during a two-year surveying phase in which the van-sized OSIRIS-REx spacecraft orbited Bennu and broke the record as the smallest spacecraft to orbit a small body.

Presented at the opening day of the American Astronomical Society’s Division for Planetary Sciences meeting on Oct. 26, the paper details the first observations and measurements of impact craters on individual boulders on an airless planetary surface since the Apollo missions to the moon 50 years ago, according to the authors.

The publication comes just a few days after a major milestone for NASA’s University of Arizona-led OSIRIS-REx mission. On Oct. 20, the spacecraft successfully descended to asteroid Bennu to grab a sample from its boulder-scattered surface – a first for NASA. The sample has now been successfully stowed and will be returned to Earth for study in 2023, where it could give scientists insight into the earliest stages of the formation of our solar system.

Impact Craters on Rocks Tell a Story

Although Earth is being pelted with more than 100 tons of space debris each day, it is virtually impossible to find a rockface pitted by impacts from small objects at high velocities. Courtesy of our atmosphere, we get to enjoy any object smaller than a few meters as a shooting star rather than having to fear being struck by what essentially amounts to a bullet from outer space.

Planetary bodies lacking such a protective layer, however, bear the full brunt of a perpetual cosmic barrage, and they have the scars to show for it. High-resolution images taken by the OSIRIS-REx spacecraft during its two-year survey campaign allowed researchers to study even tiny craters, with diameters ranging from a centimeter to a meter, on Bennu’s boulders.

On average, the team found boulders of 1 meter (3 feet) or larger to be scarred by anywhere from one to 60 pits – impacted by space debris ranging in size from a few millimeters to tens of centimeters.

“I was surprised to see these features on the surface of Bennu,” said the paper’s lead author, Ronald Ballouz, a postdoctoral researcher in the UArizona Lunar and Planetary Laboratory and a scientist with the OSIRIS-REx regolith development working group. “The rocks tell their history through the craters they accumulated over time. We haven’t observed anything like this since astronauts walked on the moon.”

This composite image of a boulder on Bennu’s surface shows the cascading rim of one of the asteroid’s ancient craters that originated while Bennu resided in the asteroid belt. The image combines photos from OSIRIS-REx and reconstructed shape models built from the OSIRIS-REx laser altimeter instrument. The overlaid colors highlight the topography of the boulder (warmer colors are higher elevation). ©University of Arizona/Johns Hopkins APL/York University.

For Ballouz, who grew up during the 1990s in post-civil war Beirut, Lebanon, the image of a rock surface pitted with small impact craters evoked childhood memories of building walls riddled with bullet holes in his war-torn home country.

“Where I grew up, the buildings have bullet holes all over, and I never thought about it,” he said. “It was just a fact of life. So, when I looked at the images from the asteroid, I was very curious, and I immediately thought these must be impact features.”

The observations made by Ballouz and his team bridge a gap between previous studies of space debris larger than a few centimeters, based on impacts on the moon, and studies of objects smaller than a few millimeters, based on observations of meteors entering Earth’s atmosphere and impacts on spacecraft.

“The objects that formed the craters on Bennu’s boulders fall within this gap that we don’t really know much about,” Ballouz said, adding that rocks in that size range are an important field of study, mainly because they represent hazards for spacecraft in orbit around Earth. “An impact from one of these millimeter to centimeter-size objects at speeds of 45,000 miles per hour can be dangerous.”

Ballouz and his team developed a technique to quantify the strength of solid objects using remote observations of craters on the surfaces of boulders – a mathematical formula that allows researchers to calculate the maximum impact energy that a boulder of a given size and strength could endure before being smashed. In other words, the crater distribution found on Bennu today keeps a historical record of the frequency, size and velocity of impact events the asteroid has experienced throughout its history.

“The idea is actually pretty simple,” Ballouz said, using a building exposed to artillery fire as an analogy to boulders on an asteroid. “We ask, ‘What is the largest crater you can make on that wall before the wall disintegrates?’ Based on observations of multiple walls of the same size, but with different sized craters, you can get some idea of the strength of that wall.”

The same holds true for a boulder on an asteroid or other airless body, said Ballouz, who added that the approach could be used on any other asteroid or airless body that astronauts or spacecraft may visit in the future.

“If a boulder gets hit by something larger than an object that would leave a certain size cater, it would just disappear,” he explained. In other words, the size distribution of boulders that have persisted on Bennu serve as silent witnesses to its geologic past.

A Newcomer to Earth’s Neighborhood

Applying the technique to boulders ranging in size from pebbles to parking garages, the researchers were able to make inferences about the sizes and type of impactors to which the boulders were exposed, and for how long.

The authors conclude that the largest craters on Bennu’s boulders were created while Bennu resided in the asteroid belt, where impact speeds are lower than in the near-Earth environment, but are more frequent and often near the limit of what the boulders could withstand. Smaller craters, on the other hand, were acquired more recently, during Bennu’s time in near-Earth space, where impact speeds are higher but potentially disruptive impactors are much less common.

Based on these calculations, the authors determine that Bennu is a relative newcomer to Earth’s neighborhood. Although it is thought to have formed in the main asteroid belt more than 100 million years ago, it is estimated that it was kicked out of the asteroid belt and migrated to its current territory only 1.75 million years ago. Extending the results to other near-Earth objects, or NEOs, the researchers also suggest that these objects likely come from parent bodies that fall in the category of asteroids, which are mostly rocky with little or no ice, rather than comets, which have more ice than rock.

While theoretical models suggest that the asteroid belt is the reservoir for NEOs, no observational evidence of their provenance was available other than meteorites that fell to Earth and were collected, Ballouz said. With these data, researchers can validate their models of where NEOs come from, according to Ballouz, and get an idea of how strong and solid these objects are – crucial information for any potential missions targeting asteroids in the future for research, resource extraction or protecting Earth from impact.

References: Ballouz, R., Walsh, K.J., Barnouin, O.S. et al. Bennu’s near-Earth lifetime of 1.75 million years inferred from craters on its boulders. Nature (2020). https://doi.org/10.1038/s41586-020-2846-z link: http://dx.doi.org/10.1038/s41586-020-2846-z

Provided by University of Arizona

Ten Things to Know About Bennu (Planetary Science)

NASA’s first mission to return a sample from an ancient asteroid arrived at its target, the asteroid Bennu, on Dec. 3, 2018. This mission, the Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer, or OSIRIS-REx, is a seven-year long voyage set to conclude upon the delivery to Earth of at least 2.1 ounces (60 grams) and possibly up to almost four and a half pounds (two kilograms) of sample. It promises to be the largest amount of extraterrestrial material brought back from space since the Apollo era. The 20-year anniversary of the asteroid’s discovery was in September 2019 — and scientists have been collecting data ever since. Here’s what we already know (and some of what we hope to find out) about this pristine remnant from the early days of our solar system.

Video: Now, thanks to laser altimetry data and high-resolution imagery from OSIRIS-REx, we can take a tour of Bennu’s remarkable terrain.
Credits: NASA’s Goddard Space Flight Center

1) IT’S VERY, VERY DARK…

Bennu is classified as a B-type asteroid, which means it contains a lot of carbon in and along with its various minerals. Bennu’s carbon content creates a surface on the asteroid that reflects about four percent of the light that hits it — and that’s not a lot. For contrast, the solar system’s brightest planet, Venus, reflects around 65 percent of incoming sunlight, and Earth reflects about 30 percent. Bennu is a carbonaceous asteroid that hasn’t undergone drastic, composition-altering change, meaning that on and below its deeper-than-pitch-black surface are chemicals and rocks from the birth of the solar system.

This mosaic image of asteroid Bennu is composed of 12 PolyCam images collected on Dec. 2, 2018 by the OSIRIS-REx spacecraft from a range of 15 miles (24 km).
Credits: NASA/Goddard/University of Arizona

2) …AND VERY, VERY OLD.

Bennu has been (mostly) undisturbed for billions of years. Not only is it conveniently close and carbonaceous, it is also so primitive that scientists calculated it formed in the first 10 million years of our solar system’s history — over 4.5 billion years ago. Thanks to the Yarkovsky effect — the slight push created when the asteroid absorbs sunlight and re-emits that energy as heat — and gravitational tugs from other celestial bodies, it has drifted closer and closer to Earth from its likely birthplace: the Main Asteroid Belt between Mars and Jupiter.

3) BENNU IS A “RUBBLE-PILE” ASTEROID — BUT DON’T LET THE NAME TRICK YOU.

Is Bennu space trash or scientific treasure? While “rubble pile” sounds like an insult, it’s actually a real astronomy classification. Rubble-pile asteroids like Bennu are celestial bodies made from lots of pieces of rocky debris that gravity compressed together. This kind of detritus is produced when an impact shatters a much larger body (for Bennu, it was a parent asteroid around 60 miles [about 100 km] wide). Bennu, for contrast, is about as tall as the Empire State Building. It likely took just a few weeks for these shards of space wreckage to coalesce into the rubble-pile that is Bennu. Bennu is full of holes inside, with 20 to 40 percent of its volume being empty space. The asteroid is actually in danger of flying apart, if it starts to rotate much faster or interacts too closely with a planetary body.

4) ASTEROIDS MAY HARBOR HINTS ABOUT THE ORIGIN OF ALL LIFE ON EARTH…

Bennu is a primordial artifact preserved in the vacuum of space, orbiting among planets and moons and asteroids and comets. Because it is so old, Bennu could be made of material containing molecules that were present when life first formed on Earth. All Earth life forms are based on chains of carbon atoms bonded with oxygen, hydrogen, nitrogen and other elements. However, organic material like the kind scientists hope to find in a sample from Bennu doesn’t necessarily always come from biology. It would, though, further scientists’ search to uncover the role asteroids rich in organics played in catalyzing life on Earth.

5) …BUT ALSO PLATINUM AND GOLD!

Extraterrestrial jewelry sounds great, and Bennu is likely to be rich in platinum and gold compared to the average crust on Earth. Although most aren’t made almost entirely of solid metal (but asteroid 16 Psyche may be!), many asteroids do contain elements that could be used industrially in lieu of Earth’s finite resources. Closely studying this asteroid will give answers to questions about whether asteroid mining during deep-space exploration and travel is feasible. Although rare metals attract the most attention, water is likely to be the most important resource in Bennu. Water (two hydrogen atoms bound to an oxygen atom) can be used for drinking or separated into its components to get breathable air and rocket fuel. Given the high cost of transporting material into space, if astronauts can extract water from an asteroid for life support and fuel, the cosmic beyond is closer than ever to being human-accessible.

6) SUNLIGHT CAN CHANGE THE ASTEROID’S ENTIRE TRAJECTORY.

Gravity isn’t the only factor involved with Bennu’s destiny. The side of Bennu facing the Sun gets warmed by sunlight, but a day on Bennu lasts just 4 hours and 17.8 minutes, so the part of the surface that faces the Sun shifts constantly. As Bennu continues to rotate, it expels this heat, which gives the asteroid a tiny push towards the Sun by about 0.18 miles (approximately 0.29 kilometers) per year, changing its orbit.

7) THERE IS A SMALL CHANCE THAT BENNU WILL IMPACT EARTH LATE IN THE NEXT CENTURY.

The NASA-funded Lincoln Near-Earth Asteroid Research team discovered Bennu in 1999. NASA’s Planetary Defense Coordination Office continues to track near-Earth objects (NEOs), especially those like Bennu that will come within about 4.6 million miles (7.5 million kilometers) of Earth’s orbit and are classified as potentially hazardous objects. Between the years 2175 and 2199, the chance that Bennu will impact Earth is only 1-in-2,700, but scientists still don’t want to turn their backs on the asteroid. Bennu swoops through the solar system on a path that scientists have confidently predicted, but they will refine their predictions with the measurement of the Yarkovsky Effect by OSIRIS-REx and with future observations by astronomers.

8) SAMPLING BENNU WILL BE HARDER THAN WE THOUGHT.

Early Earth-based observations of the asteroid suggested it had a smooth surface with a regolith (the top layer of loose, unconsolidated material) composed of particles less than an inch (a couple of centimeters) large — at most. As the OSIRIS-REx spacecraft was able to take pictures with higher resolution, it became evident that sampling Bennu would be far more hazardous than what was previously believed: new imagery of Bennu’s surface show that it’s mostly covered in massive boulders, not small rocks. OSIRIS-REx was designed to be navigated within an area on Bennu of nearly 2,000 square yards (meters), roughly the size of a parking lot with 100 spaces. Now, it must maneuver to a safe spot on Bennu’s rocky surface within a constraint of less than 100 square yards, an area of about five parking spaces.

9) BENNU WAS NAMED AFTER AN ANCIENT EGYPTIAN DEITY.

Bennu was named in 2013 by a nine-year-old boy from North Carolina who won the Name that Asteroid! competition, a collaboration between the mission, the Planetary Society, and the LINEAR asteroid survey that discovered Bennu. Michael Puzio won the contest by suggesting that the spacecraft’s Touch-and-Go Sample Mechanism (TAGSAM) arm and solar panels resemble the neck and wings in illustrations of Bennu, whom ancient Egyptians usually depicted as a gray heron. Bennu is the ancient Egyptian deity linked with the Sun, creation and rebirth — Puzio also noted that Bennu is the living symbol of Osiris. The myth of Bennu suits the asteroid itself, given that it is a primitive object that dates back to the creation of the Solar System. Themes of origins and rebirth are part of this asteroid’s story. Birds and bird-like creatures are also symbolic of rebirth, creation and origins in various ancient myths.

10) BENNU IS STILL SURPRISING US!

The spacecraft’s navigation camera observed that Bennu was spewing out streams of particles a couple of times each week. Bennu apparently is not only a rare active asteroid (only a handful of them have been as of yet identified), but possibly with Ceres explored by NASA’s Dawn mission, among the first of its kind that humanity has observed from a spacecraft. More recently, the mission team discovered that sunlight can crack rocks on Bennu, and that it has pieces of another asteroid scattered across its surface. More pieces will be added to Bennu’s cosmic puzzle as the mission progresses, and each brings the solar system’s evolutionary history into sharper and sharper focus.

Provided by Nasa

SwRI Scientists Study The Rugged Surface Of Near-Earth Asteroid Bennu (Planetary Science)

As the days count down to NASA’s OSIRIS-REx spacecraft’s Touch-And-Go asteroid sample collection attempt, Southwest Research Institute scientists have helped determine what the spacecraft can expect to return from the near-Earth asteroid Bennu’s surface. Three papers published online by Science on Oct. 8 discuss the color, reflectivity, age, composition, origin and distribution of materials that make up the asteroid’s rough surface.

As NASA’s OSIRIS-REx spacecraft’s Touch-And-Go asteroid sample collection attempt approaches, Southwest Research Institute scientists have helped determine what the spacecraft can expect to return from the near-Earth asteroid Bennu’s surface. SwRI scientists also played a role in sample site selection, including the primary site Nightingale shown here. ©NASA/Goddard/University of Arizona

On October 20, the spacecraft will descend to the asteroid’s boulder-strewn surface, touch the ground with its robotic arm for a few seconds and collect a sample of rocks and dust – marking the first time NASA has grabbed pieces of an asteroid for return to Earth. SwRI scientists played a role in the selection of the sample sites. The first attempt will be made at Nightingale, a rocky area 66 feet in diameter in Bennu’s northern hemisphere. If this historic attempt is unsuccessful, the spacecraft will try again at a secondary site.

Since the spacecraft arrived at Bennu in 2018, scientists have been characterizing the asteroid’s composition and comparing it to other asteroids and meteorites. The mission discovered carbon-bearing compounds on Bennu’s surface, a first for a near-Earth asteroid, as well as minerals containing or formed by water. Scientists also studied the distribution of these materials, globally and at the sample sites

“Our recent studies show that organics and minerals associated with the presence of water are scattered broadly around Bennu’s surface, so any sample returned to Earth should contain these compounds and minerals,” said SwRI’s Dr. Vicky Hamilton, a coauthor on all three papers. “We will compare the sample’s relative abundances of organics, carbonates, silicates and other minerals to those in meteorites to help determine the scenarios that best explain Bennu’s surface composition.”

Asteroid Bennu is a dark, rubble pile held together by gravity and thought to be the collisional remnant of a much larger main-belt object. Its rubble-pile nature and heavily cratered surface indicates 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.

“Boulders strewn about near the Nightingale site have bright carbonate veins,” Hamilton said. “Bennu shares this compositional trait with aqueously altered meteorites. This correlation suggests that at least some carbonaceous asteroids were altered by percolating water in the early Solar System.”

The boulders on Bennu have diverse textures and colors, which may provide information about their variable exposure to micrometeorite bombardment and the solar wind over time. Studying color and reflectance data provide information about the geologic history of planetary surfaces.

“Bennu’s diverse surface includes abundant primitive material potentially from different depths in its parent body plus a small proportion of foreign materials from another asteroid family littered about its surface,” said SwRI’s Dr. Kevin Walsh, a coauthor of one of the papers. “In addition, both the primary and back-up sample sites, Nightingale and Osprey, are situated within small spectrally reddish craters that are thought to be more pristine, having experienced less space weathering than most of Bennu’s bluish surface.”

The OSIRIS-REx team is also comparing Bennu to Ryugu, another near-Earth asteroid. Both asteroids are thought to have originated from primitive asteroid families in the inner main belt. The Japan Aerospace Exploration Agency launched Hayabusa2 in 2014 and rendezvoused with near-Earth asteroid Ryugu in 2018. After surveying the asteroid for a year and a half, the spacecraft collected samples and is expected to return to Earth December 6, 2020.

The sample returned by OSIRIS-REx, combined with the surface context maps OSIRIS-REx has collected, will improve interpretations of available ground and space telescope data for other primitive dark asteroids. Comparing returned Bennu samples with those of Ryugu will be instrumental for understanding the diversity within, and history of, asteroid families and the entire asteroid belt.

Provided by Southwest Research Institute