Like boot prints on the Moon, NASA’s OSIRIS-REx spacecraft left its mark on asteroid Bennu. Now, new images — taken during the spacecraft’s final fly-over on April 7 — reveal the aftermath of its historic encounter with the asteroid.

Bennu’s surface was disturbed in three different ways: by the force of the spacecraft touching down; by the sampling mechanism, which collected material by blowing gas into its collection filter; and by four of the spacecraft’s back-away thrusters, which moved the spacecraft away from the sample site and agitated dust and boulders on the surface. The image above shows the TAG site and highlights a large boulder thrown about 40 feet (about 12 meters). Credit: NASA/Goddard/University of Arizona

The spacecraft flew within 2.3 miles (3.7 km) of the asteroid — the closest it has been since the Touch-and-Go, or TAG, sample collection event on Oct. 20, 2020. During TAG, the spacecraft’s sampling head sunk 1.6 feet (48.8 centimeters) into the asteroid’s surface and simultaneously fired a pressurized charge of nitrogen gas, churning up surface material and driving some into the collection chamber. The spacecraft’s thrusters also launched rocks and dust during the maneuver to reverse course and safely back away from the asteroid.

Comparing the two images reveals obvious signs of surface disturbance. At the sample collection point, there appears to be a depression, with several large boulders evident at the bottom, suggesting that they were exposed by sampling. There is a noticeable increase in the amount of highly reflective material near the TAG point against the generally dark background of the surface, and many rocks were moved around.

View of the Nightingale sample site before the TAG event. Images were taken on March 7, 2019, by the spacecraft’s PolyCam instrument, as part of the mission’s global mapping campaign. Credit: NASA/Goddard/University of Arizona

Where thrusters fired against the surface, substantial mass movement is apparent. Multiple sub-meter boulders were mobilized by the plumes into a campfire ring–like shape — similar to rings of boulders seen around small craters pocking the surface.

Jason Dworkin, the mission’s project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, noticed that one boulder measuring 4 feet (1.25 meters) across on the edge of the sampling site seemed to appear only in the post-TAG image. “The rock probably weighs around a ton, with a mass somewhere between a cow and a car.”

Dante Lauretta, of the University of Arizona and the mission’s principal investigator, later pointed out that this boulder is likely one of those present in the pre-TAG image, but much nearer the sampling location, and estimates it was thrown a distance of 40 feet (about 12 meters) by the sample collection event.

In order to compare the before and after images, the team had to meticulously plan this final flyover. “Bennu is rough and rocky, so if you look at it from a different angle or capture it at a time when the sun is not directly overhead, that dramatically changes what the surface looks like,” says Dathon Golish, a member of the OSIRIS-REx image processing working group, headquartered at the University of Arizona. “These images were deliberately taken close to noon, with the Sun shining straight down, when there’s not as many shadows.”

View of the Nightingale sample site after the TAG event. Images were taken on April 7, 2021, as part of a final observation campaign to document the state of the surface after TAG. Credit: NASA/Goddard/University of Arizona

“These observations were not in the original mission plan, so we were excited to go back and document what we did,” Golish said. “The team really pulled together for this one last hurrah.”

The spacecraft will remain in Bennu’s vicinity until departure on May 10, when the mission will begin its two-year return cruise back to Earth. As it approaches Earth, the spacecraft will jettison the Sample Return Capsule (SRC) that contains the sample from Bennu. The SRC will then travel through Earth’s atmosphere and land under parachutes at the Utah Test and Training Range on Sept. 24, 2023.

Once recovered, the capsule will be transported to the curation facility at NASA’s Johnson Space Center in Houston, where the sample will be removed for distribution to laboratories worldwide, enabling scientists to study the formation of our solar system and Earth as a habitable planet. NASA will set 75% of the sample aside for future generations to study with technologies not invented yet.

The OSIRIS-REx mission is the first NASA mission to visit a near-Earth asteroid, survey the surface, and collect a sample to deliver to Earth.

NASA’s Goddard Space Flight Center in Greenbelt, Maryland, provides overall mission management, systems engineering, and the safety and mission assurance for OSIRIS-REx. Dante Lauretta of the University of Arizona, Tucson, is the principal investigator, and the University of Arizona also leads the science team and the mission’s science observation planning and data processing. Lockheed Martin Space in Denver built the spacecraft and provides flight operations. Goddard and KinetX Aerospace 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, D.C.

For more information about OSIRIS-REx visit: https://www.nasa.gov/osiris-rex

By Mikayla Mace Kelley
University of Arizona, Tucson, Ariz.

and by Rani Gran
NASA’s Goddard Space Flight Center, Greenbelt, Md.

NASA’s OSIRIS-REx completed its last flyover of Bennu in around 6 am (EDT), 4am (MDT) April 7^th and is now slowly drifting away from the asteroid; however, the mission team will have to wait a few more days to find out how the spacecraft changed the surface of Bennu when it grabbed a sample of the asteroid.

This image shows a top-down view of asteroid Bennu, with a portion of the asteroid’s equatorial ridge and northern hemisphere illuminated. It was taken by the PolyCam camera on NASA’s OSIRIS-REx spacecraft on March 4, from a distance of about 186 miles (300 km). Credit: NASA/Goddard/University of Arizona

The OSIRIS-REx team added this flyby to document surface changes resulting from the Touch and Go (TAG) sample collection maneuver October 20, 2020. “By surveying the distribution of the excavated material around the TAG site, we will learn more about the nature of the surface and subsurface materials along with the mechanical properties of the asteroid,” said Dr. Dante Lauretta, Principal Investigator for OSIRIS-REx at the University of Arizona.

During the flyby, OSIRIS-REx imaged Bennu for 5.9 hours, covering more than a full rotation of the asteroid. It flew within 2.1 miles (3.5 kilometers) distance to the surface of Bennu – the closest it’s been since the TAG sample collection event.

It will take until at least April 13^th for OSIRIS-REx to downlink all of the data and new pictures of Bennu’s surface recorded during the flyby. It shares the Deep Space Network Antennae with other missions like Mars Perseverance, and typically gets 4-6 hours of downlink time per day. “We collected about 4,000 megabytes of data during the flyby,” said Mike Moreau, Deputy Project Manager of OSIRIS-REx at NASA Goddard Spaceflight Center. “Bennu is approximately 185 million miles from Earth right now, which means we can only achieve a downlink data-rate of 412 kilobits per second, so it will take several days to download all of the flyby data.”

Once the mission team receives the images and other instrument data, they will study how OSIRIS-REx jumbled up Bennu’s surface. During touchdown, the spacecraft’s sampling head sunk 1.6 feet (48.8 centimeters) into the asteroid’s surface and simultaneously fired a pressurized charge of nitrogen gas. The spacecraft’s thrusters kicked up a large amount of surface material during the back-away burn – launching rocks and dust in the process.

KinetX Flight Navigator, Leilah McCarthy, processes navigation images to help target NASA’s OSIRIS-REx final flyby of Bennu. Credit: KinetX Inc./Coralie Adam

OSIRIS-REx, with its pristine and precious asteroid cargo, will remain in the vicinity of Bennu until May 10 when it will fire its thrusters and begin its two-year cruise home. The mission will deliver the asteroid sample to Earth September 24, 2023.

NASA invites the public to watch OSIRIS-REx depart from Bennu on NASA.gov and NASA TV, at 4 PM EDT.

NASA’s Goddard Space Flight Center in Greenbelt, Maryland, provides overall mission management, systems engineering, and the safety and mission assurance for OSIRIS-REx (Origins Spectral Interpretation Resource Identification Security – Regolith Explorer). Dante Lauretta of the University of Arizona, Tucson, is the principal investigator, and the University of Arizona also leads the science team and the mission’s science observation planning and data processing. Lockheed Martin Space in Denver built the spacecraft and provides flight operations. Goddard and KinetX Aerospace 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.

Written by Rani Gran.

For more information about this story and OSIRIS-REx visit: https://www.nasa.gov/osiris-rex

NASA’s OSIRIS-REx mission is on the brink of discovering the extent of the mess it made on asteroid Bennu’s surface during last fall’s sample collection event. On Apr. 7, the OSIRIS-REx spacecraft will get one last close encounter with Bennu as it performs a final flyover to capture images of the asteroid’s surface. While performing the flyover, the spacecraft will observe Bennu from a distance of about 2.3 miles (3.7 km) – the closest it’s been since the Touch-and-Go Sample Collection event on Oct. 20, 2020.

This artist’s concept shows the planned flight path of NASA’s OSIRIS-REx spacecraft during its final flyby of asteroid Bennu, which is scheduled for April 7. Credit: NASA/Goddard/University of Arizona

The OSIRIS-REx team decided to add this last flyover after Bennu’s surface was significantly disturbed by the sample collection event. During touchdown, the spacecraft’s sampling head sunk 1.6 feet (48.8 centimeters) into the asteroid’s surface and simultaneously fired a pressurized charge of nitrogen gas. The spacecraft’s thrusters also mobilized a substantial amount of surface material during the back-away burn. Because Bennu’s gravity is so weak, these various forces from the spacecraft had a dramatic effect on the sample site – launching many of the region’s rocks and a lot of dust in the process. This final flyby of Bennu will provide the mission team an opportunity to learn how the spacecraft’s contact with Bennu’s surface altered the sample site and the region surrounding it.

The single flyby will mimic one of the observation sequences conducted during the mission’s Detailed Survey phase in 2019. OSIRIS-REx will image Bennu for 5.9 hours, which is just over a full rotation period of the asteroid. Within this timeframe, the spacecraft’s PolyCam imager will obtain high-resolution images of Bennu’s northern and southern hemispheres and its equatorial region. The team will then compare these new images with the previous high-resolution imagery of the asteroid obtained during 2019.

Most of the spacecraft’s other science instruments will also collect data during the flyover, including the MapCam imager, the OSIRIS-REx Thermal Emission Spectrometer (OTES), the OSIRIS-REx Visible and Infrared Spectrometer (OVIRS), and the OSIRIS-REx Laser Altimeter (OLA). Exercising these instruments will give the team a chance to assess the current state of each science instrument onboard the spacecraft, as dust coated the instruments during the sample collection event. Understanding the health of the instruments is also part of NASA’s evaluation of possible extended mission opportunities after the sample is delivered to Earth.

After the Bennu flyby, it will take several days for the data from the flyover to be downlinked to Earth. Once the data are downlinked, the team will inspect the images to understand how OSIRIS-REx disturbed the asteroid’s surface material. At this point, the team will also be able to evaluate the performance of the science instruments.

The spacecraft will remain in asteroid Bennu’s vicinity until May 10, when the mission will enter its Return Cruise phase and begin its two-year journey back to Earth. As it approaches Earth, the spacecraft will jettison the Sample Return Capsule (SRC) that contains the rocks and dust collected from Bennu. The SRC will then travel through the Earth’s atmosphere and land under parachutes at the Utah Test and Training Range on Sep. 24, 2023.

Once recovered, the capsule will be transported to the curation facility at the agency’s Johnson Space Center in Houston, where the sample will be removed for distribution to laboratories worldwide, enabling scientists to study the formation of our solar system and Earth as a habitable planet.

NASA’s Goddard Space Flight Center in Greenbelt, Maryland, provides overall mission management, systems engineering, and the safety and mission assurance for OSIRIS-REx. Dante Lauretta of the University of Arizona, Tucson, is the principal investigator, and the University of Arizona also leads the science team and the mission’s science observation planning and data processing. Lockheed Martin Space in Denver built the spacecraft and provides flight operations. Goddard and KinetX Aerospace 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.