A treasure trove of pristine asteroid samples is arriving at Earth this weekend
After 7 years in deep space, a NASA spacecraft is nearly home again with a delivery of precious cargo from an asteroid dating back to the solar system's birth, over four and a half billion years ago.
On September 8, 2016, NASA's OSIRIS-REx mission blasted into space. Its mission: travel to near-Earth asteroid 101955 Bennu, spend more than three years there, mapping its surface, exploring its structure and composition, and then become NASA's first spacecraft to touch the surface of an asteroid, collect a sample, and return that sample to Earth for study.
This artist's rendition shows OSIRIS-REx's trajectory for orbiting asteroid Bennu and approaching to 'tag' the surface for a sample. Credit: NASA
Now, after more than seven years, that mission is nearly complete!
OSIRIS-REx (an acronym for "Origins, Spectral Interpretation, Resource Identification and Security – Regolith Explorer") imaged the entirety of asteroid Bennu's surface. It also used the Canadian OLA instrument (the OSIRIS-REx Laser Altimeter) to produce highly detailed terrain maps that were crucial for pinpointing the location where the spacecraft would collect a sample of Bennu for return to Earth.
On October 20, 2020, the spacecraft performed its Touch-And-Go (TAG) sample collection, during which the sample arm unexpectedly sank roughly half a metre into Bennu's surface. Then, on May 10, 2021, the probe departed Bennu and has been journeying back to Earth since.
WATCH: See a NASA spacecraft collect sample from asteroid Bennu's surface
Now, OSIRIS-REx is approaching home, on a trajectory to swing past Earth on September 24. When it does, the spacecraft will release the small capsule where it stowed the pristine asteroid fragments gathered from Bennu during the TAG maneuver. This capsule will plunge into Earth's atmosphere and then parachute to the surface, where it is expected to touch down in the Utah desert.
The OSIRIS-REx sample collection aimed to gather at least 60 grams (2 ounces) of material from Bennu.
Due to the amount of dust and rock kicked up during the TAG maneuver, the mission team is confident that the sample container carries much more than the minimum amount they hoped for. The latest estimates put the amount of material at anywhere between 150-350 grams. However, there could be even more.
The final tally will be taken once the capsule has touched down, they have returned it to Johnson Space Center in Houston, and the scientists there can open the capsule in a clean lab specially prepared to receive these samples.
Canada's role
OSIRIS-REx isn't just a NASA mission. The Canadian Space Agency (CSA) also played a significant role — the very first sample return mission for Canada — and Canadian scientists are involved in every facet of the mission.
The OSIRIS-REx Laser Altimeter (OLA) instrument was designed and built by Canadian space technology company MacDonald, Dettwiler and Associates (MDA) and supplied to the mission by the CSA.
This infographic explains OLA, the OSIRIS-REx Laser Altimeter, and how it contributed to the overall mission to Bennu. Credit: CSA
Led by Michael Daly and Jeff Seabrook at York University, OLA became critical for the success of OSIRIS-REx. Before the spacecraft got close to Bennu, it was assumed that the asteroid was essentially a giant boulder in space, with perhaps a few rocks and a thin layer of dust on its surface. This would have made OSIRIS-REx's cameras more than sufficient for mapping a sample location.
However, when the mission team saw the first close-up images of Bennu's chaotic, boulder-strewn surface, they realized they would need more than just images to plan the remainder of the mission. The highly accurate 3D model of the asteroid constructed from OLA data made it possible for the sample collection part of the mission to go forward.
WATCH: Canadian technology made this 3D map of Bennu possible
Samples for Canada
Due to Canada's role in OSIRIS-REx, four per cent of the total amount of material returned by the mission is coming here for study. Researchers at five institutions nationwide will be part of the efforts to analyze these samples — from York University, the University of British Columbia, the University of Winnipeg, the University of Calgary, and the Royal Ontario Museum (ROM) in Toronto.
Dr. Kim Tait, the Curator of Mineralogy at the ROM, has been focusing her studies over the past few years on carbonaceous chondrite meteorites. These are meteorites that contain the most carbon and are composed of minerals formed in the presence of water. According to Dr. Tait, they are the same kinds of rocks that make up asteroid Bennu.
These charcoal-black meteorite fragments are from the Tagish Lake meteorite, which fell on January 18, 2000, and were recovered just hours after they struck the ground. These meteorites are some of the most pristine we know about. Pieces of this meteorite are being studied at the University of Alberta and the Royal Ontario Museum. Credit: Chris Herd/University of Alberta
"What I focus on are the minerals," Dr. Tait told The Weather Network. "How the minerals are forming, how they formed together, and which minerals are present. It all reads like a book. I can read the different pressures, the temperatures, and the elements that were present."
Meteorites can tell us a lot about asteroids and the conditions at the beginning of the solar system. However, since they fall to Earth from space, they may not show us the complete picture. Their trip through the atmosphere and exposure to Earth's environment can change them.
This image, taken on March 7, 2019, by the PolyCam camera on NASA's OSIRIS-REx spacecraft from a distance of about 5 km, shows a view across asteroid Bennu's southern hemisphere and into space. It demonstrates the number and distribution of boulders across Bennu's surface. The large, light-coloured boulder just below the center of the image is about 7.4 meters wide, which is roughly half the width of a basketball court. Credits: NASA/Goddard/University of Arizona
The samples returning with OSIRIS-REx are directly from the source; they will be protected during their ride down to Earth's surface and kept in isolation in the lab until scientists can study them.
"This is like a snapshot in time, from the very beginning of the solar system, and some of these materials could be pre-solar system," Tait explained. "Getting our hands on a very primitive sample, that's full of carbon, which can be the building blocks of life, is super exciting."
Why Bennu?
Bennu is of specific interest to researchers for two reasons.
First, because the asteroid is composed of ancient materials, which have likely been virtually unchanged for billions of years. Examining those materials up close will give scientists a clear view of the conditions at the birth of our solar system.
This view of Bennu is stitched together from 12 separate images taken by OSIRIS-REx's PolyCam instrument when the spacecraft was just 24 kilometers from the asteroid. Credit: NASA/Goddard/University of Arizona
Second, NASA considers Bennu to be a potentially hazardous asteroid. It crosses Earth's orbit and occasionally comes relatively close to our planet. There is even a tiny chance — 0.037 per cent, or about 1 in 2,700 — that it will strike Earth exactly 159 years from the day OSIRIS-REx drops off its samples (September 24, 2182). While the asteroid's proximity makes it easier for us to get a spacecraft there than to other asteroids, it also means that at some point, we may need to change Bennu's path around the Sun to prevent an impact with Earth in the future.
One complication for this is Bennu's structure. For an asteroid that's one solid mass, you can hit it with a spacecraft or maybe even attach a rocket that can push it away from Earth. Bennu isn't just one piece, though. It is essentially a rubble pile — a bunch of boulders, smaller rocks, and dust floating through space, all clumped together by the weak gravitational pull between all the pieces.
This sketch details Bennu's origin and size and gives an idea of the most likely internal structure of the asteroid. Credit: James Tuttle Keane/Nature Geosciences
When OSIRIS-REx's sample arm touched the surface of Bennu during the sample collection, it sunk into the surface roughly half a metre. The materials were so loosely packed together that, although it looked solid enough, the mission scientists said the TAG maneuver met with so little resistance it was like punching a ball pit.
"If this thing is just held together by 'static cling', compared to a solid mass, if we want to divert or change its direction, we'll have to use different methods compared to if it was one big solid piece," Dr. Tait said.
