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Last week, NASA took a sample from the surface of asteroid Bennu, a body the size of an Empire State Building that scientists at the Southwest Research Institute helped map with near-unprecedented accuracy. Using orbital data from the OSIRIS-REx spacecraft, the researchers measured craters ranging in size from one centimeter to one meter on the boulders scattered across its irregular surface to shed light on the age of the asteroid.
While the collected sample will yield tremendous scientific value when it is returned to Earth in 2023, a key work for scientists during the Bennu orbiting period has been to understand the geology of the entire asteroid to provide important context for the sample. This provides information on any processes that may have influenced the nature of the sample.
“The incredible data collected by OSIRIS-REx on the asteroid Bennu allowed us not only to find impact craters on its surface, but to actually find and study the craters on the surface of the boulders,” said Dr. Kevin Walsh of SwRI. coauthor of “Bennu’s near-Earth lifespan of 1.75 million years was inferred from the craters on its boulders,” he published Oct. 26 in the journal Nature. “The craters that we were able to observe and measure on the surface of the boulders allowed us to estimate their strength, a unique measure of its kind”.
Bennu is a heap of dark debris held together by gravity and thought to be an asteroid remnant created following a collision involving an object larger than the main belt. The boulders are scattered across its heavily cratered surface, indicating that it has had a troubled life since it was released from its much larger parent asteroid millions or even billions of years ago. Scientists use impact crater studies to determine the age of planetary surfaces.
Team members from the University of Arizona have developed a mathematical formula that allows researchers to calculate the maximum impact energy a boulder of a given size and force could withstand before being destroyed.
Walsh, lead author of Dr. Ron Ballouz (a postdoctoral fellow at the University of Arizona), and colleagues have put together an understanding of the number of craters, the strength of the affected materials, and the number of impactors to help limit the chronology of Bennu’s existence in the inner Solar System to 1.75 million years.
Since the spacecraft arrived at Bennu in 2018, scientists have characterized the asteroid’s composition from orbit and comparing it to other asteroids and meteorites. Now NASA has collected an actual sample of its surface for scientists to study.
“We held our breath when the spacecraft hit the boulder-strewn surface of the asteroid with a robotic arm for a few seconds to collect a sample of rock and dust on October 20 – a first for NASA,” Walsh said. “Hitting the dirty money on the first try is fantastic. We can’t wait to learn a lot more when the champion returns to Earth in 2023.”
The manuscript describes a method for measuring the strength of solid objects that uses remote observations of craters on surface boulders. Determining the strength of boulders on the surface of asteroids is a leap forward compared to measuring the strength of much smaller meteorites, which have a tendency to survive passage through Earth’s atmosphere.
“The rocks tell their story through the craters accumulated over time,” Ballouz said. “The boulders serve as a witness to Bennu’s time as a near-Earth asteroid, validating decades of dynamic studies of the life of near-Earth asteroids.”
Related links
Planetary Science at Southwest Research Institute
News, science and technology on asteroid and comet missions
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First scientific instrument installed on Lucy
San Antonio TX (SPX) November 3, 2020
Before NASA’s Lucy mission could begin its long journey to Trojan asteroids, the first science camera delivered to the spacecraft had to travel 1,500 miles across the continental United States. The Lucy LOng Range Reconnaissance Imager (L’LORRI) traveled from the Johns Hopkins Applied Physics Laboratory (APL), in Laurel, Maryland, where it was built and tested, to Lockheed Martin Space, in Littleton, Colorado, where it is located the assembled spacecraft. Was safely received in L … read more
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