Bennu & OSIRIS-REx

As humans, we’re engrossed by the physics and metaphysics of beginnings. How did the universe arise? If we banged into reality in a big way, what existed beforehand? Did a creator create or did we spontaneously congeal?

The answers to these cosmological questions might be beyond the grasp of beings designed to perceive the universe in four dimensions.

Answers about a beginning far closer to home, however, could be within our grasp. How did our solar system come to fruition? How did the Sun’s satellites become orbs and why did they end up where they did? How did the building blocks of life materialize on Earth?

Many astronomers obsess over these queries and, unlike the Big Bang, we can actually send our technology to places that might illuminate the solar system’s evolution. To that end, on 8 September 2016, NASA launched OSIRIS-REx into the abyss, hoping to gather evidence about how our starry neighborhood emerged.

OSIRIS-REx before launch - photo by NASA

OSIRIS-REx stands for Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer.

Rolls right off the tongue.

Regolith is defined as the layer of loose rocky material that overlays bedrock. This part of the spacecraft’s name is critical, as it points to the gist of its mission. NASA wanted OSIRIS-REx to fly to an asteroid, scoop up some loose rocks from its surface, and send the sample back to Earth.

And they didn’t want to visit just any asteroid. From an original list of half a million candidates, the selection committee used a few criteria to narrow down potential targets. They wanted an asteroid close to Earth to optimize timelines, maneuverability, and efficiency. They hoped to find one with low eccentricity, low inclination, and an orbital radius of 0.8-1.6 astronomical units. These factors cut the list down greatly, to just 192 Near Earth Objects

Then, they wanted an asteroid that featured regolith. It would be far easier to land on a body with loose rock and gather some of the pebbles than it would be to land on a smooth rock and drill. This parameter limited the search to asteroids with diameters greater than 200 meters. Smaller bodies spin too fast to retain the regolith layers. This benchmark trimmed the list to 26 asteroids.

Finally, they wanted to select an asteroid with a specific composition. They needed an asteroid filled with carbon compounds and wanted it to be a so-called “primitive,” one that is ancient and largely unchanged in the past 4 billion years. With carbonaceous compounds such as organic molecules and amino acids, in an unchanged state, we might be able to understand how the building blocks of life populated our solar system. Combining all these standards, just five asteroids checked all the boxes.

Of the five, one happens to zoom closely by Earth every six years. On an astronomical scale, very closely: 0.002 AU. That’s about 185,000 miles. For reference, the Moon is 238,900 miles away. Between 2178 and 2290, this asteroid has a 1-in-1,750 chance of hitting Earth. This potential cataclysm prompted NASA to choose a stone called Bennu.

A mosaic image of Bennu from OSIRIS-REx
Bennu - graphic by Jeff Dahl

In 2012, scientists held a contest to name the asteroid. A third-grader named Michael Puzio thought the OSIRIS-REx craft, with its extended arm, looked like a heron. He proposed Bennu, which was a mythological Egyptian bird, usually portrayed as a heron. This idea had a nice synergy with Osiris, the Egyptian god of the dead, so Bennu it was.

Scientists took the neat step to continue the bird theme, promising to name any features of Bennu after avians.

After traveling through the cosmos for two years, OSIRIS-REx arrived at Bennu. For the next 505 days, it mapped the surface of the asteroid from a distance of about 5 kilometers (3.1 miles), looking for the perfect spot to land. Four finalists emerged, so they all got the bird treatment:

The potential Bennu sample sites - photo by NASA

In the end, the team chose the Nightingale site.

On 20 October 2020, after two trial runs, OSIRIS-REx “touched down” on Bennu. Some news outlets used the term “pogo-sticked” to describe the incredible maneuver. The spacecraft extended an arm before the entirety of OSIRIS-REx neared the surface of the asteroid. Instead of landing and obtaining a sample of the regolith, the arm smashed into Bennu, snagged its rock, and pushed back into space in one motion.

An incredible feat.

After this maneuver, OSIRIS-REx bounded back to space and jettisoned a package with a piece of Bennu. The destination was Earth. Almost two years later, on 24 September 2023, a capsule descended into the Utah desert, carrying a payload that might help us unlock the beginnings of our solar system.

Because we live in an era of technological wonder, we sent a craft to an asteroid, picked up some of its rocks, sent it back to Earth, and we could watch the parachute open live. The two videos that follow are from the same NASA stream but start at different points. The first displays the capsule rushing to the surface before the chute opens for a soft landing. The second displays a dude casually approaching this unique payload.

The capsule hurtles toward Utah

Just a gift from an asteroid, no big deal

After scientists retrieved the sample, it was moved to the laboratory. With any luck, we’ll soon have some more insight into how organic molecules came to proliferate on Earth or, at least, a better picture of the early days of our solar system.

As time moves forward, these space missions seem to hold less sway among the public, perhaps because they have become somewhat – I hesitate to utilize this word – routine. That we can send a craft to a zooming hunk of rock, snag a sample with precision, send it back, and start to analyze it is nothing short of wondrous.

Though Bennu’s part in this story is over, OSIRIS-REx is not destined to sit darkly in space. NASA renamed the craft OSIRIS-APEX because they sent it on a new mission. This time, it will image the near-Earth asteroid called Apophis (APophis Explorer). If all goes well, sometime in 2029, OSIRIS-APEX will pogo into Apophis in an attempt to disturb its surface, hoping to tell us about its composition.

Apophis is the Greek name for Apep, an Egyptian deity known as the enemy of Ra. An evil serpent that lives in eternal darkness, Apep is the Uncreator, who tries nightly to swallow Ra. In 2029, Apophis the asteroid will pass just 19,600 miles above the surface of Earth, which is lower than our geosynchronous satellites.

Let’s hope Apophis doesn’t swallow us.

Further Reading and Exploration

OSIRIS-REx – Official Mission Website

101955 Bennu – NASA

WHY BENNU? – Asteroid Mission/University of Arizona

NASA’s First Asteroid Sample Has Landed, Now Secure in Clean Room – NASA

Osiris-Rex: Asteroid Bennu ‘is a journey back to our origins’ – BBC

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