On Sept. 24, 2023, NASA's OSIRIS-REx became the first U.S. mission to deliver a sample of an asteroid to Earth. The spacecraft, which launched Sept. 8, 2016, collected rocks and dust – an estimated 8.8 ounces, or 250 grams – from the surface of asteroid Bennu on Oct. 20, 2020. After further study of the asteroid, the spacecraft began its cruise back to Earth with the sample on May 10, 2021.
The material gathered from Bennu acts as a time capsule from the earliest days of our solar system and will help us answer big questions about the origins of life and the nature of asteroids.
OSIRIS-REx released its sample capsule toward Earth’s atmosphere at 6:42 a.m. EDT (4:42 a.m. MDT) on Sept. 24, 2023. The spacecraft was 63,000 miles (102,000 kilometers) from Earth’s surface at the time – about one-third the distance from Earth to the Moon.
Traveling at 27,650 mph (44,500 kph), the capsule pierced the atmosphere at 10:42 a.m. EDT (8:42 a.m. MDT), off the coast of California at an altitude of about 83 miles (133 kilometers). It landed at the Department of Defense’s Utah Test and Training Range near Salt Lake City at 10:52 a.m. EDT (8:52 a.m. MT). Along the way, two parachutes successfully deployed to stabilize and slow the capsule down to a gentle 11 mph (18 kph) at touchdown.
Radar, infrared, and optical instruments in the air and on the ground tracked the capsule to its landing coordinates inside a 36-mile by 8.5-mile (58-kilometer by 14-kilometer) area on the range. Within several minutes, the recovery team was dispatched to the capsule’s location to inspect and retrieve it. The team found the capsule in good shape, and then determined it was safe to approach. Within 70 minutes, they had wrapped it up for safe transport to a temporary clean room on the range.
The Bennu sample was transported in its unopened canister by aircraft to NASA’s Johnson Space Center in Houston on Sept. 25, 2023. Curation scientists will disassemble the canister, extract and weigh the sample, create an inventory of the rocks and dust, and, over time, distribute pieces of Bennu to scientists worldwide.
Scientists predict that Bennu formed from pieces of a larger asteroid in the asteroid belt after a catastrophic collision between 1 and 2 billion years ago. Considered a “rubble-pile” asteroid, Bennu is an amalgamation of rocks that are loosely packed and barely held together by gravity or other forces. The asteroid is relatively rich in organic molecules. Its materials also appear to have been chemically altered by liquid water in the distant past, likely when it was still part of the larger asteroid it came from. A major question in science is: how did Earth come to have an abundance of organic molecules and liquid water, two key ingredients for life as we know it? Scientists say that asteroids like Bennu could have delivered these ingredients through collisions with Earth billions of years ago.
Here are three of the many reasons NASA chose to study Bennu.
- The asteroid is a remnant from the tumultuous formation of the solar system, unlike any rocks we can find on Earth. On our planet, weather, erosion, and plate tectonics have wiped away evidence of Earth’s formation. Thus, Bennu’s rocks offer us insight into our own history – a time about 4.5 billion years ago when Earth was first forming.
- Bennu is rich in organic compounds that make up all known life. There is evidence that asteroids like Bennu delivered these compounds to Earth when they smashed into our planet billions of years ago when the conditions for life were starting to emerge. Scientists want to learn more about this early period, and samples of a well-preserved asteroid could help them do that.
- Most asteroids can be found in the asteroid belt, a ring of asteroids that circles the Sun between the orbits of Mars and Jupiter. The asteroid belt is very far away, so a round trip would take a long time and be much harder to do. Bennu, in contrast, crosses Earth’s orbit, so it was easier and quicker to send a spacecraft to Bennu and back.
Bennu has no chance of hitting Earth through the mid 2100s. After that, the chance is very slight, 1 in 1,750, or less than one-tenth of a percent, through at least the year 2300. In the distant future, Bennu could potentially hit Earth or even Venus, but that cannot be predicted with any accuracy. Indeed, being able to accurately predict the future motions of asteroids like Bennu is one of the science goals of the mission.
Because scientists will look for organic molecules related to life in grains of Bennu, it is critical that the sample doesn’t get exposed to Earth’s environment, including its life. Such contamination would make it hard for scientists to distinguish which molecules came from space and which came from Earth.
As the sample capsule descended through Earth’s atmosphere, air entering through its vents was filtered to remove contaminants including water vapor, organic compounds, and dust.
Once the capsule landed, it was retrieved, and delivered to a temporary clean room at the Utah Test and Training Range. The OSIRIS-REx team hooked it up to a tank that released nitrogen, a gas that doesn’t interact with most other chemicals. A continuous nitrogen flow into the capsule pushed out any invading air.
The asteroid sample is safe for Earth and its inhabitants. Due to the harsh radiation environment in space, there is no chance that the sample from Bennu could contain living organisms. Based on studies of other materials from space, including meteorites, cosmic dust, and previously returned samples by NASA and JAXA (Japan Aerospace Exploration Agency), we know that hazardous chemicals or harmful levels of radioactive materials will also not be found in Bennu samples.
About 20 minutes after the spacecraft released its sample capsule above Earth’s atmosphere, it fired its engines to divert its trajectory away from Earth. The spacecraft then set out on a new mission called OSIRIS-APEX (OSIRIS–Apophis Explorer) to explore asteroid Apophis, which it will reach in 2029.
Within minutes after the sample capsule landed, a mission team was dispatched to the capsule’s location to inspect and retrieve it. The team found the capsule in good shape, and then determined it was safe to approach. Within 70 minutes, they had it wrapped up for safe transport to a temporary clean room on the range.
The Bennu sample was transported in its unopened canister by aircraft to NASA’s Johnson Space Center in Houston on Sept. 25, 2023. Curation scientists there will extract and weigh the sample, create an inventory of Bennu's rocks and dust, and, over time, distribute pieces of Bennu to scientists worldwide.
Up to a quarter of the sample will be distributed to 233 scientists on the OSIRIS-REx team who represent 38 institutions globally; 4% will be given to the Canadian Space Agency, and 0.5% to JAXA (Japan Aerospace Exploration Agency). The rest, about 70%, will be preserved at NASA’s Johnson Space Center (and White Sands) for scientists outside the mission team and for future generations of scientists.