Female Speaker: How do scientists choose an asteroid to visit? Join the 3-2-1 science team as we explore why OSIRIS-REx is going to Bennu. Asteroids can address some big questions about our origins and destiny like how did the solar system form? What kinds of materials exist in the solar system? How did life evolve in the solar system? Can we mine asteroid resources? And are asteroids bringers of life or death or both?
Bringing back a sample for scientists to study will provide some answers to these questions, but which asteroid will give us the biggest bang for our buck or give us the most knowledge for the least cost and effort?
Today, we know of over 600,000 asteroids, mostly in the main belt between Mars and Jupiter. Collisional dynamics, thermal forces and the gravitational effects of the giant planets pushed some asteroids out of the belt and into the inner solar system. These are called Near Earth Asteroids, or NEAs for short. Because they’re closer to Earth, they’re easier to reach, so OSIRIS-REx scientists narrowed their search to this group to find the perfect target asteroid.
It takes a lot of time and a lot of fuel to travel to an asteroid, so optimizing the trip is important. NEAs with earthlike orbits require minimal energy, meaning we can get there using the lift provided by our rocket. Fewer than 1,000 asteroids have optimal orbits for a sample return mission. The asteroid we visit can’t be too small or rotating too rapidly. Some very small asteroids less than 200 metres in diameter can rotate as quickly as once every minute. This is risky for spacecraft operations and might have ejected all loose materials before we arrive, so we wouldn’t get a good sample. Only under 100 NEAs are big enough and rotate slowly enough for safe operations and with ample regolith to collect.
OSIRIS-REx scientists want a sample from the earliest time in the solar system to learn about the origin of life. They want an asteroid that is organic rich and has volatiles like oxygen and hydrogen. Under 10 of the remaining asteroids are carbonaceous.
Astronomers have studied the candidates in detail, and they’ve gotten lots of data about Bennu onits close approaches to Earth, making it the best candidate for an accessible, volatile and organic rich remnant of the early solar system. And as it happens, Bennu has a high probability for an asteroid of impacting the Earth in about 200 years, so it’s a good idea to visit and learn as much as we can about its orbit before it intersects Earth.
For more information about Bennu, OSIRIS-REx and asteroids, click on the links.
This video is an OSIRIS-REx production. OSIRIS-REx is a partnership of the University of Arizona, NASA, Goddard Space Flight Centre and Lockheed Martin.