Question 1

Why did NASA send a spacecraft to sample the asteroid Bennu?

Accepted Answer

First, there’s the scientific reason. This is a small step toward answering a fundamental question: “Why are we here?” Bennu contains rocks that date to the earliest epoch of the solar system. The mission is designed to give scientists samples of these “fossils” that date back 4 billion years. The molecular makeup of the material brought back to Earth could provide clues to how it became an ocean planet, with the kind of environment where life could appear (and eventually evolve into complex organisms such as astrobiologists). Although NASA has never previously sampled an asteroid, Hayabusa2, a mission led by Japan’s space agency, brought back samples in 2020 of a different, and much larger, asteroid called Ryugu. Beyond the science, there’s the issue of planetary defense. Bennu could spell trouble. Its orbit crosses Earth’s, and there is a small chance it could hit us some time in the coming centuries. NASA keeps track of such “near-Earth objects” (including comets) that might pose collision risks, and right now Bennu is at the top of NASA’s list of potentially hazardous space rocks. It is not the biggest asteroid out there, but its problematic orbit justifies keeping a close eye on it. NASA’s DART mission last year demonstrated that it is possible to fly a spacecraft into an asteroid and change its motion. The space agency would still like to know more about the composition of these dangerous near-Earth objects and how they might potentially be diverted, which is part of what scientists will study using the sample from Bennu.

Question 2

When might Bennu collide with Earth?

Accepted Answer

Not soon. Not in anyone’s lifetime, unless human longevity changes dramatically. In fact, it might never hit Earth. But in 2182, it has a roughly 1 in 2,700 chance of impacting our planet, according to a calculation published in 2021. That calculation will be refined after Bennu makes a close pass by Earth in 2135.

Question 3

How big is Bennu?

Accepted Answer

The asteroid has a diameter of 500 meters (about 1,640 feet). That’s not nearly as big as the object that hit Earth 66 million years ago and closed the book on dinosaurs (other than the ones we call birds). But if Bennu hits Earth, that will be a bad day.

Question 4

What did OSIRIS-REx collect?

Accepted Answer

The sampler device at the end of a robotic arm of the spacecraft plunged into Bennu’s surface about 20 inches deep and emerged with a mixture of material known as regolith. How much is in the sample, exactly, is unknown. Some spilled during the maneuver, but mission leaders believe they have about 250 grams (about 8.8 ounces) of material, plus or minus 101 grams. To meet the mission’s stated goal, there needs to be at least 60 grams in the capsule.

Question 5

Is the OSIRIS-REx mission officially a success?

Accepted Answer

This was a triumph of aerospace engineering. The technical challenges were immense, including the complexities of guiding a spacecraft into orbit around a small object many millions of miles away. It is not possible to joystick such maneuvers, so the spacecraft had to function autonomously as it carried out the delicate sampling operation on the asteroid’s surprisingly rough, boulder-strewn surface. Until the spacecraft got close to Bennu, no one realized the degree to which it was just a loosely aggregated “rubble pile.” Now comes the science. Success may ultimately be defined by what, exactly, scientists learn from the Bennu bits once they can study them in the lab.

Question 6

What is the coolest word used by scientists who study things like asteroids and planets?

Accepted Answer

“Ephemeris.” NASA defines it as “a tabulation of computed positions and velocities (and/or various derived quantities such as right ascension and declination) of an orbiting body at specific times.” Plural: ephemerides.

Question 7

Why is the mission called OSIRIS-REx?

Accepted Answer

Because the acronym is much easier to say than the full name, which is Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer. Osiris is the name of an ancient Egyptian god, and Dante Lauretta, the lead scientist on the mission, is a mythology buff who thought the name would work well. Now that the spacecraft has a new target, OSIRIS-REx has been renamed OSIRIS-APEX, for OSIRIS-Apophis Explorer.

A NASA capsule carrying pieces of an asteroid successfully lands in Utah