OSIRIS-REx has successfully completed its primary mission: to collect a sample of material from asteroid Bennu, pack it up into a capsule, and fly back to Earth. After seven years in space, and a few billion miles around the Sun (to save fuel), the orbits of our planet and the spacecraft crossed again, allowing the precious delivery of the first-ever US asteroid sample return to be made.
The cosmic package – signed, sealed, and delivered – landed safely in the US Air Force's Utah Test and Training Range on Sunday, September 24 at 8:52 am local time (2:52 pm UTC). It was collected in a helicopter in a well-rehearsed approach and taken to a special kitted-up room to avoid Earthly contamination. Protective items like the heat shield and back shell will be removed there and nitrogen will be used to remove oxygen and moisture from the sample canister.
Tomorrow morning a Boeing C-17 plane will fly the capsule down to NASA’s Johnson Space Center and that is where the fun begins.
Why was Bennu chosen for the asteroid sample?
Asteroid Bennu, the most dangerous known asteroid, is a window into the very beginning of the Solar System. A primitive space rock that has remained mostly unaltered for billions of years, studying its physical and chemical properties could give us hints about the building blocks of planets as they were forming 4.5 billion years ago.
Bennu is a rubble pile, loosely held together by gravity. OSIRIS-REx was able to estimate the density and porosity (the amount of empty space) of the whole asteroid but this can now be checked and compared with what is gleaned by the sample.
“When we can compare [density and porosity of Bennu] with the actual specimens we have in the laboratory, we can get a better idea of the overall structure of the asteroid,” Brother Bob Macke, the curator of meteorites at the Vatican Observatory who built a custom device to study the asteroid samples, told IFLScience.
“The amount of pore space in the whole asteroid versus the amount of pore space in the rock will tell how much empty space there Is between the rocks in the asteroid, which will help us to understand better how it's put together and help constrain our models of how it formed.”
Macke has developed an instrument to measure the density and porosity of cosmic material: a pycnometer. But it's not just the physical characteristics that are intriguing. Scientists around the world want to study the chemistry of Bennu as well.
“The first sample we'll get will be a little vial of tiny little bits of powder, and we'll pick out bits from that and CT scan them so we'll be able to look at the structure of them and get an idea of its composition,” Professor Sara Russell, part of the OSIRIS-REx Sample Analysis Team from the Natural History Museum, London, told IFLScience.
“Then we'll put it in an electron microscope, which will enable us to do some element mapping. So we'll see what elements are in there and that will tell us what minerals we're looking at. We'll do some X-ray diffraction, which looks at the crystal structure. And all of that will kind of give us this picture of what kind of object it is.”
How do the samples travel across the world? The answer is very carefully and probably with an unusual custom declaration form.
All that data will provide insights into not just what makes up Bennu but also into the many meteorites here on Earth. Before the first-ever return of an asteroid sample by Japan's Hayabusa mission, followed by Hayabusa-2, and OSIRIS-REx, meteorites were the way we studied the building blocks of the Solar System, but we don’t always know where they come from. This sample will provide some context on that front too.
“We'll be able to say whether it's like any known meteorite or if it's something completely different,” Professor Russell explained.
How do you get a piece of Asteroid Bennu?
The mission's goal was to collect about 60 grams (2 ounces) of rubble and dust from the Bennu's surface. However, NASA estimates that between 400 and 1,000 grams (14-35 ounces) of material was actually collected so there is plenty of it to go around. It will be shared among different institutes around the world that will put their expertise and equipment to use to analyze this priceless material.
So how do the samples travel across the world? The answer is very carefully and probably with an unusual custom declaration form.
“We're going to hand carry them. So either me or a colleague will go over and collect them from the Johnson Space Center,” Professor Russell explained to IFLScience. “But the Johnson Space Center is also happy to send them by courier as well. Actually, we had to rehearse this. Everything in this mission is so well rehearsed.”
Now the sample has arrived on Earth and instead of the end, the curtain is rising and the orchestra is finishing the overture. Incredible science from Bennu is about to begin. But OSIRIS-REx, rather than bowing out after a mission served, is moving on. From studying the most dangerous known near-Earth asteroid its new focus is another notorious space rock: asteroid Apophis. That calls for a change of name.
Apophis will come within 32,000 kilometers (20,000 miles) of Earth in 2029, less than one-tenth the distance between the Moon and Earth. OSIRIS-APEX should get into orbit not long after this close approach to study how these close encounters affect near-Earth asteroids.