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NASA spacecraft makes historic touchdown on ancient asteroid Bennu to collect dust and pebbles from its surface

OSIRIS-REx is scheduled to return to Earth in 2023 with the sample and promises to be the largest amount of extraterrestrial material brought back from space since the Apollo era
(NASA/Goddard/University of Arizona)
(NASA/Goddard/University of Arizona)

“Transcendental, I mean, I can’t believe we actually pulled this off,” said Dante Lauretta, principal investigator of the NASA mission, the first such mission that briefly touched an asteroid to collect dust and pebbles from the surface for delivery to Earth in 2023. On October 20, the agency’s OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) made a historic touchdown on the well-preserved, ancient asteroid, known as Bennu, which is currently more than 200 million miles or 321 million kilometers from Earth.

This will be the first US mission to carry samples from an asteroid back to Earth, and the largest sample returned from space since the Apollo era. Bennu offers scientists a window into the early solar system as it was first taking shape billions of years ago and flinging ingredients that could have helped seed life on Earth. “Bennu may contain the molecular precursors to the origin of life and the Earth’s oceans. Bennu is also one of the most potentially hazardous asteroids, as it has a relatively high probability of impacting the Earth late in the 22nd century. OSIRIS-REx will determine Bennu’s physical and chemical properties, which will be critical to know in the event of an impact mitigation mission. Asteroids like Bennu contain natural resources such as water, organics, and precious metals. In the future, these asteroids may one day fuel the exploration of the solar system by robotic and crewed spacecraft,” explains NASA.

Preliminary data showed that the sample collection event went as planned. The OSIRIS-REx team will begin to assess whether the spacecraft grabbed any material, and, if so, how much. The goal is at least 60 grams, which is roughly equivalent to a full-size candy bar. If Tuesday’s sample collection event, known as “Touch-And-Go (TAG),” provided enough of a sample, mission teams will command the spacecraft to begin stowing the precious cargo to begin its journey back to Earth in March 2021. Otherwise, they will prepare for another attempt in January. The spacecraft carried out TAG autonomously, with pre-programmed instructions from engineers on Earth. 

“After over a decade of planning, the team is overjoyed at the success of today’s sampling attempt. Even though we have some work ahead of us to determine the outcome of the event – the successful contact and back-away from Bennu are major accomplishments for the team. I look forward to analyzing the data to determine the mass of sample collected,” said Lauretta, OSIRIS-REx principal investigator at the University of Arizona in Tucson.”

What is this mission?

OSIRIS-REx seeks answers to the questions that are central to the human experience: Where did we come from? What is our destiny? Asteroids, the leftover debris from the solar system formation process, can answer these questions and teach scientists about the history of the Sun and planets.

Bennu is one of the most potentially hazardous asteroids, as it has a relatively high probability of impacting the Earth late in the 22nd century (Getty Images)

OSIRIS-REx was launched from Cape Canaveral Air Force Station in Florida on September 8, 2016. It arrived at its target, the asteroid Bennu, on December 3, 2018, and began orbiting the asteroid for the first time on December 31, 2018. It 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. The spacecraft is scheduled to return to Earth on September 24, 2023, when it will parachute the sample return capsule (SRC) into Utah's west desert where scientists will be waiting to collect it.

What happened on October 20?

At 1.50 pm EDT, OSIRIS-REx fired its thrusters to nudge itself out of orbit around Bennu. It extended the shoulder, then elbow, then wrist of its 11-foot (3.35-meter) sampling arm, known as the Touch-And-Go Sample Acquisition Mechanism (TAGSAM), and transited across Bennu while descending about a half-mile (805 meters) toward the surface. After a four-hour descent, at an altitude of approximately 410 feet (125 meters), the spacecraft executed the “Checkpoint” burn, the first of two maneuvers to allow it to precisely target the sample collection site, known as ‘Nightingale.’

About 10 minutes later, the spacecraft fired its thrusters for the second ‘matchpoint’ burn to slow its descent and match the asteroid’s rotation at the time of contact. It then continued an 11-minute coast past a boulder the size of a two-story building, nicknamed “Mount Doom,” to touchdown in a clear spot in a crater on Bennu’s northern hemisphere. The size of a small parking lot, the Nightingale site is one of the few relatively clear spots on this unexpectedly boulder-covered space rock.


It will take about a week for the OSIRIS-REx team to confirm how much sample the spacecraft collected. “Today’s TAG maneuver was historic. The fact that we safely and successfully touched the surface of Bennu, in addition to all the other milestones this mission has already achieved, is a testament to the living spirit of exploration that continues to uncover the secrets of the solar system,” emphasized Lori Glaze, Planetary Science Division director at NASA headquarters in Washington. 

OSIRIS-REx engineers and scientists will use several techniques to identify and measure the sample remotely. They will compare images of the Nightingale site before and after TAG to see how much surface material moved around in response to the burst of gas. The team will then try to determine the amount of sample collected. 

To store the sample, engineers will command the robotic arm to place the sample collector head into the sample return capsule, located in the body of the spacecraft. The sample arm will then retract to the side of the spacecraft for the final time, the SRC will close, and the spacecraft will prepare for its departure from Bennu in March 2021 — this is the next time Bennu will be properly aligned with Earth for the most fuel-efficient return flight. However, if the scientists determine that the spacecraft did not collect enough sample at Nightingale, it will attempt another TAG maneuver on January 12, 2021. If that happens, it will touchdown at the backup site called “Osprey,” which is another relatively boulder-free area inside a crater near Bennu’s equator.