Scientists say the touch and landing of NASA’s OSIRIS-REx spacecraft on an asteroid last month revealed new insights into the structure of loose rocks that can cover the surfaces of many small planetary bodies – material that is more like a field of ball games than a solid rock base.
The structure of the outermost layer of the asteroid is evident in images captured by the OSIRIS-REx spacecraft as it descended into the airless world more than 200 million miles (330 million kilometers) from Earth on October 20.
The next day, NASA released images of a narrow-angle camera aimed at the spacecraft’s robotic arm, 3.4 meters long. A sampling device the size of a dinner plate at the end of the arm fired a bottle of compressed nitrogen gas when the spacecraft came into contact with the surface of the Bennu asteroid, a small planetary body measuring about a third of a mile. diameter.
The discharge of nitrogen gas helped to force the asteroid samples into the collection chamber. After six seconds on the surface of the asteroid, OSIRIS-REx fired propellers to move away from Bennu.
Later, scientists received close-up images of the sample collection head, showing it stuffed with material taken from the surface of the asteroid. Some asteroid particles were visible escaping from the collection chamber, which led managers to command the spacecraft to store the sample head inside its return to Earth capsule earlier than expected, minimizing sample loss.
The sampling device was sealed inside the return capsule of the OSIRIS-REx spacecraft on October 28.
At the end of last week, authorities released another series of images taken during the spacecraft’s touch and landing. These were captured by a wide-angle navigation camera on OSIRIS-REx.
According to the scientific team at OSIRIS-REx, images from the navigation camera – or NavCam – were captured over a period of approximately three hours. The sequence begins about an hour after OSIRIS-REx performed an exit orbit maneuver to begin its descent, and ends about two minutes after the spacecraft retreated, officials said.
A spin, or rotation, maneuver is visible in the middle of the image sequence as OSIRIS-REx points its sampling arm towards the target sampling location on asteroid Bennu, a region called “Nightingale”.
“As the spacecraft approaches the Nightingale site, the shadow of the sampling arm appears at the bottom of the frame. Shortly thereafter, the sampling head strikes the Nightingale location (outside the camera’s field of view, in the upper right corner) and fires a bottle of nitrogen gas, which mobilizes a substantial amount of material from the sample location, “wrote the OSIRIS team -REx in a description of the NavCam images.
“Several seconds later, the spacecraft performs a recoil burn and the shadow of the sampling arm is visible against the disturbed surface material. The team continues to investigate what caused the extremely dark areas visible in the upper and middle parts of the painting ”, wrote the team. “The upper area may be the edge of the depression created by the sampling arm, a strong shadow cast by material raised from the surface or some combination of the two.
“Likewise, the medium dark region that appears first in the lower left corner of the image may be a depression caused by one of the spacecraft’s propellants during firing, a shadow caused by high material or a combination of both.”
The OSIRIS-REx spacecraft built by Lockheed Martin relied on the black and white images from the navigation camera to guide itself autonomously to a safe touch zone in Bennu. The navigation algorithms compared the images from the camera to a pre-loaded map on the spacecraft’s computer, helping OSIRIS-REx to determine its location in relation to the asteroid.
With its sample protected in the return capsule, OSIRIS-REx is expected to depart from the vicinity of the asteroid Bennu next year to begin its journey back to Earth. The spacecraft will launch the return capsule to re-enter Earth’s atmosphere and land at Utah Test and Training Camp on September 24, 2023.
NASA’s $ 1 billion Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer mission, launched on September 8, 2016, from Cape Canaveral, aboard a United Launch Alliance Atlas 5 rocket. The main objective of OSIRIS-REx is to return samples of asteroids to Earth for detailed analysis by scientists, who hope to discover clues about the origins of the solar system.
The mission requirement was that OSIRIS-REx would collect at least 60 grams, or 2.1 ounces, of asteroid material. Scientists said before October 20 that the spacecraft could collect much more, and evidence suggests that it probably captured more than 2.2 pounds, or 1 kilogram, of asteroid specimens, according to Dante Lauretta, the lead investigator for the mission at the University of Arizona.
Data from the brief touch on the asteroid indicated that the spacecraft’s robotic arm sank up to 19 inches (48 centimeters) into the soft surface of Bennu.
Although the scientific result of the mission waits until the asteroid samples return to Earth, Lauretta said on Thursday that scientists are already learning about Bennu’s physical characteristics.
The spacecraft detected small particles flying from Bennu shortly after it reached the asteroid in December 2018. These particles look similar to the flake material that leaked from TAGSAM’s head.
“It looks like a box of corn flakes in space,” said Lauretta. “And they are floating in a random motion. They are coming from the TAGSAM head for the most part, but they are colliding with each other. They are spinning and falling. We can solve many of them.
“So it’s a great set of image calibration data to better understand the particle ejection events and the particle trajectories that we observed throughout the encounter with the asteroid,” said Lauretta. “Although my heart was broken by the loss of the sample, it ended up being a very cool scientific experiment.”
OSIRIS-REx’s contact with the asteroid’s surface on October 20 also provided a rich set of data, suggesting that the outer layer of the asteroid’s soil and low-density rocks lacked much cohesion. The spacecraft’s robotic arm touched the asteroid when the OSIRIS-REx approached just 0.2 mph, or 10 centimeters per second, about a tenth of the speed of a typical walk.
“When TAGSAM’s head made contact with the regolith, it simply flowed like a fluid,” said Lauretta. “And I think this is what would happen to an astronaut if she tried to walk on the surface of the asteroid. It would sink to your knees or deeper – depending on how loose the soil was – until you hit a bigger rock or some kind of rock. “
He said the “terrestrial truth” data collected by OSIRIS-REx will help scientists reexamine models of asteroid geology.
“It is fascinating that there was so little resistance to the spacecraft from the surface of the asteroid,” said Lauretta. “Basically, it’s like a ball pit on a child’s playground. You kind of jump on it and just sink.
“Fortunately, we had those recoil thrusters to reverse the direction of movement, or we could have just flown across the asteroid,” joked Lauretta.
The new measurements of the density of asteroids from OSIRIS-REx will help scientists refine assessments of the impact risk that Bennu may pose to Earth. Scientists calculated a 1 in 2,700 probability that Bennu could reach Earth in the late 20th century.
Much of the asteroid can burn in the Earth’s atmosphere due to its porosity.
“Thermal analysis indicates that a lot of the material on Bennu’s surface – particularly the large black rugged rocks that are a major component of the surface – they appear to have material properties that would not survive the passage through the atmosphere intact,” said Lauretta. . “They would fragment and much of the material would be lost.”
This means that the immaculate specimens collected at Bennu are different from any meteorites or asteroid fragments that fell to Earth and reached the surface intact.
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