The robotic arm with the sample collector at the end will be extended and then the spacecraft will be nudged into a spin on Saturday. “We’re measuring a property called the moment of inertia,” Dr. Lauretta said.
The scientists will compare the rate of spin to what they measured before collecting a sample. Just as a skater with outstretched arms holding a barbell would spin slower than a skater holding nothing, OSIRIS-REX will spin slower depending on how much material was picked up.
Scientists are hoping for at least a couple of ounces, but it could be more than four pounds.
“The precision, just like everything on this program, is phenomenal,” Dr. Lauretta said. “We’re talking tens of grams of precision on a measurement on a spacecraft hundreds of millions of miles away.”
If by unlucky chance OSIRIS-REX came up empty on Tuesday, it can try two more times.
The collection of the asteroid sample is the climax of the $800 million mission, which launched four years ago. The spacecraft has been making detailed observations of Bennu — a rock as wide as the Empire State Building is tall — for two years, mapping features of its surface as small as a couple of inches wide. It even discovered that Bennu was shooting debris from its surface into space.
The mission’s controllers selected a spot inside a crater near Bennu’s north pole that they named Nightingale. The spacecraft, 20 feet wide and about the size of a sport utility vehicle, had to navigate carefully to the target site, which is only 26 feet in diameter. In addition, it had to avoid a wall of rocks on the eastern edge of the crater. That included a pointy pillar nicknamed Mount Doom, which is as tall as a two- or three-story building.
However, despite the risks, Nightingale offered the greatest potential scientific payoffs, with unobstructed fine-grained material that appears to contain carbon-rich minerals.
Asteroids, mostly located in orbits between Mars and Jupiter, are bits that never coalesced into a planet, and planetary scientists hope that the samples from Bennu could shed light on what the young solar system was like when it formed 4.5 billion years ago. Asteroids like Bennu, which possesses carbon-rich minerals, may have provided the building blocks for life to arise on Earth.