On the evening of Sept. 8, an Atlas 5 is scheduled to launch NASA’s latest planetary science mission. That spacecraft will travel to the asteroid Bennu, spending several years there studying the asteroid and collecting samples from its surface before returning to Earth in 2023. Its name: the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer, or OSIRIS-REx.
It’s a mouthful of a name, but it’s meant to be descriptive of the multiple goals of the mission, not all purely scientific. “The mission objectives are captured in the awesome acronym that is OSIRIS-REx,” said Dante Lauretta, the University of Arizona planetary scientist who is the principal investigator for the mission, at a NASA briefing Aug. 17.
The “Origins” part of the mission’s name refers to the fact that Bennu is thought to be an unaltered remnant of the solar system’s formation 4.5 billion years ago. “This is really the driver of our science. We seek samples that date back to the very dawn of our solar system,” Lauretta said.
That includes trace amounts of organic compounds that might have seeded the early Earth with the building blocks for life. “We’re going after compounds that are literally at the part-per-billion level in these materials,” he said. “We have to get these samples into our laboratories.”
The “Spectral Interpretation” part of OSIRIS-REx will collect spectroscopic data of Bennu, which will serve as “ground truth” for astronomical observations of the asteroid. That could, in turn, be applied to thousands of other asteroids observed only through telescopes. “We’re really going to be able to compare it with what we thought we learned from our telescopic observations,” Lauretta said.
There’s more to OSIRIS-REx than science, however. “Resource Identification” refers to the mission’s goal of collecting data on the composition of the asteroid, including any deposits of ice or minerals that might have more than just scientific value.
Even for an agency known for coming up with program acronyms that are in equal parts clever and convoluted, it’s a doozy.
“Resource Identification captures the interest and the investment that corporations and nations across the world are making in the potential for exploiting and developing asteroids,” said Lauretta, who also serves as an adviser for Planetary Resources, one company with asteroid mining ambitions. “We’re a trailblazer for that kind of activity because our science requires it.”
The “Security” part of the mission is part of a desire to better understand the impact threat that near Earth asteroids pose to our home planet. Bennu itself has a small chance — 1 in 2,700 — of impacting the Earth in the late 22nd Century.
OSIRIS-REx’s contribution to protecting the Earth will be to quantify a little-understood force on asteroids called the Yarkovsky Effect. That effect, caused by an asteroid absorbing sunlight and then reemitting it as thermal infrared radiation, can nudge it every so slightly in its orbit. Over time, that force can become large enough to make predictions of potential impacts unreliable.
“Regolith Explorer” refers to the study of the layer of pulverized rock — regolith — that coats the asteroid’s surface. OSIRIS-REx will examine the regolith in detail and, more importantly, capture some of it to return to Earth.
In July 2020, OSIRIS-REx will descend to the surface, extending an arm at whose tip is a device called the Touch-And-Go Sample Acquisition Mechanism, or TAGSAM. As its name suggests, it will briefly make contact with the asteroid’s surface, firing puffs of nitrogen gas that will lift some of that regolith into the device.
TAGSAM is designed to collect at least 60 grams, but project officials are optimistic they’ll get much more based on test results. “We’re routinely picking up several hundred grams,” said Lauretta.
That is still small compared to the tons of asteroid samples already on Earth in the form of meteorites. Lauretta, who started his career in meteorite science, believes the Bennu samples will be unique and interesting enough that three-fourths of them will be set aside for analysis by future generations of researchers with new instruments and new ideas.
“For me, the mission is driven by the return of pristine organic molecules from the early solar system,” he said. “I’m really hopeful that we will get some unique material that isn’t in our meteorite collections.”
Yet, he doesn’t think OSIRIS-REx is the ultimate asteroid mission. “OSIRIS-REx is really a trailblazer for all future small body missions,” he said, including commercial efforts to prospect and mine asteroids. “They’re going to take great advantage of all the pioneering techniques that OSIRIS-REx has developed.”
However, those future missions, be they scientific probes or mining spacecraft, may find it difficult to top OSIRIS-REx in one respect: its name.