The asteroid Bennu is about to have a visitor — NASA’s OSIRIS-REx spacecraft lifted off from Cape Canaveral, Florida as planned yesterday evening. It is now en route to Bennu where it will spend more than a year mapping the surface of the object from orbit. Then the real fun begins: The ultimate goal of OSIRIS-REx is to make contact with the asteroid and obtain a sample that will eventually be returned to Earth.
Studying asteroids can help scientists understand the nature of the early solar system. After all, the composition of asteroids is probably similar to that of Earth when it formed. There are, of course, plenty of samples of asteroids on Earth — they literally fall out of the sky every day. But these objects don’t tell scientists everything they’d like to know about asteroids as they exist in space. After falling through the atmosphere, an asteroid has usually been super-heated and fractured by impact. Even smaller rocks that don’t have such tremendous impact power are contaminated by their trip through the atmosphere.
To get the best data on the composition of asteroids, you need a fresh sample straight from the source. That’s where OSIRIS-REx (which stands for Origins-Spectral Interpretation-Resource Identification-Security-Regolith Explorer) comes in. The probe just left Earth aboard an Atlas V rocket, and has begun its two-year journey to Bennu. NASA says the launch went perfectly and the probe is working as expected.
When it reaches the asteroid in August of 2018, OSIRIS-REx will map the surface in extreme detail for 505 days. The next phase of the mission is where we really have to hope that NASA’s luck holds. OSIRIS-REx will approach Benuu (which is about 500 meters across) and hover just five meters above the surface. A sampling arm will extend and make contact with the surface, coping up as least 2 ounces of material from Bennu. There’s a five second timer that will trigger OSIRIS-REx to move back from the asteroid after contact is made. Ideally, this will prevent a collision and keep the thrusters off during the sample collection in order to lessen contamination.
If everything goes as planned, NASA hopes to have the sample from Bennu back on Earth in 2023. At that time, scientists will be able to look for organic molecules that could have been present on Earth as well. Bennu’s proximity to Earth makes this mission possible.
Incidentally, there’s a small chance that Bennu could hit Earth in the mid-22nd century. Knowing a little more about it could be handy down the road.