Source: NASA
What is OSIRIS-REx?
On Sept. 24, 2023, NASA’s OSIRIS-REx became the first U.S. mission to deliver a sample of an asteroid to Earth. The OSIRIS-REx 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.
This material 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.
What’s Bennu made of?
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.
Why did NASA decide to study Bennu?
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.
Will Bennu ever impact Earth?
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.
How will NASA protect the Bennu sample from Earthly contamination?
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 descends through Earth’s atmosphere, air will enter through its vents, streaming in through a filter that will remove contaminants including water vapor, organic compounds, and dust. It will then flow into a canister inside the capsule that contains the sample. This will allow the canister to come to atmospheric pressure, which will protect it from leaks that could lead to contamination.
Once the capsule lands, is retrieved, and delivered to a temporary clean room at the Utah Test and Training Range, the OSIRIS-REx team will hook it up to a tank that will release nitrogen, a gas that doesn’t interact with most other chemicals. A continuous nitrogen flow into the capsule will push out invading air.
Could the Bennu sample contaminate Earth?
The asteroid sample will be 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 on Bennu.
What happens to the OSIRIS-REx spacecraft after it delivers the sample to Earth?
About 20 minutes after the spacecraft releases its sample capsule above Earth’s atmosphere, it will fire its engines to divert its trajectory away from Earth. The spacecraft will then set out on a new mission called OSIRIS-APEX (OSIRIS–Apophis Explorer) to explore asteroid Apophis, which it will reach in 2029.
What will happen to the Bennu sample after it lands on Earth?
A team of scientists, engineers, and military safety personnel will place the capsule in a metal crate and wrap the crate in multiple sheets of a non-reactive plastic material and then a tarp. A harness will then be placed over the crate. The crate will be secured to a cable attached to a helicopter. The helicopter will fly the capsule to a temporary clean room at the Utah training range.
Scientists and engineers in the clean room will open the capsule and extract the sample canister. The next day, the mission team will transport the sample to NASA’s Johnson Space Center in Houston, where it will be documented, cared for, and stored. Soon after, portions of Bennu’s rocks and dust will be distributed to scientists on the mission’s science team, NASA’s partners from the Canadian and Japanese space agencies, and researchers around the world. A small part of the sample will also be stored in White Sands, New Mexico, for safe keeping.
Who will study the sample?
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.
