How much of asteroid Bennu is NASA's OSIRIS-REx probe delivering to Earth this weekend?

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We'll soon find out the exact amount.

side-by-side images showing a spacecraft's robotic arm about to contact a gravelly asteroid (left) and stirring up lots of dirt and rock after contact (right).
Side-by-side images from NASA's OSIRIS-REx spacecraft of the robotic arm as it descended towards the surface of asteroid Bennu (left) and as it tapped it to stir up dust and rock for sample collection (right) on Oct. 20, 2020. (Image credit: NASA's Goddard Space Flight Center)

We'll soon find out just how much asteroid dirt and rock NASA's OSIRIS-REx spacecraft collected nearly three years ago.

OSIRIS-REx's sample capsule is scheduled to come down to Earth on Sunday (Sept. 24), making a soft landing under parachutes in the Utah desert. 

That capsule is full of precious cargo — material OSIRIS-REx snagged from the surface of a 1,650-foot-wide (500 meters) near-Earth asteroid named Bennu in October 2020. Analyses of this space-rock stuff could reveal a great deal about the solar system's early days, researchers say, and might even shed light on how life got its start here on Earth.

Related: Dramatic sampling shows asteroid Bennu is nothing like scientists expected

OSIRIS-REx was tasked with grabbing at least 2 ounces (60 grams) of material during its dive down to the asteroid's surface. That dive, by the way, turned out to be surprisingly sporty: Bennu was not nearly as solid as the mission team had expected, and OSIRIS-REx's sampling arm sank deep into the space rock before popping back out again.

The spacecraft emerged with a bounty of Bennu bits — so much, in fact, that dirt and rock clogged up the sampling gear, preventing a proper seal and causing some collected material to float away into space. 

To minimize sample loss, the mission team decided to stow the Bennu material in the probe's return capsule as quickly as possible. This new plan skipped a previously planned maneuver that was supposed to spin OSIRIS-REx around a bit, in order to gather data that would allow team members to estimate the mass of the collected sample.

The mission team arrived at an estimate by other means, but it's far from precise. The number is 8.8 oz (250 g), plus or minus 3.6 oz (101 g). So, the sample capsule could contain as much as 12.4 oz (351 g), or as little as 5.2 oz (149 g).

The true number won't be known until the asteroid sample has been processed, so we'll just have to wait and see. 

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Even the low-end estimate would still be a ringing success for OSIRIS-REx, though, as it's far above the 2-oz minimum laid out in the original mission plan. 

For some perspective: Japan's Hayabusa2 spacecraft returned only about 0.18 oz (5 g) of material from the asteroid Ryugu in December 2020, and scientists have already squeezed a lot of intriguing results from that relatively small sample.

OSIRIS-REx's returned material will be stored and curated at NASA's Johnson Space Center (JSC) in Houston. The JSC team will oversee the distribution of the sample to researchers around the world, who will study it for a variety of purposes. 

One line of inquiry will focus on organic compounds, the carbon-containing building blocks of life as we know it. Scientists think carbon-rich asteroids like Bennu may have helped life get a foothold on Earth long ago, by delivering organics via impacts.

But the OSIRIS-REx spacecraft's work won't be done after it sends the sample capsule toward Earth. The probe will then set a course for the potentially hazardous asteroid Apophis, which it will reach in 2029 and study on an extended mission known as OSIRIS-APEX.

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Mike Wall
Mike Wall
Senior Space Writer

Michael Wall is a Senior Space Writer with Space.com and joined the team in 2010. He primarily covers exoplanets, spaceflight and military space, but has been known to dabble in the space art beat. His book about the search for alien life, "Out There," was published on Nov. 13, 2018. Before becoming a science writer, Michael worked as a herpetologist and wildlife biologist. He has a Ph.D. in evolutionary biology from the University of Sydney, Australia, a bachelor's degree from the University of Arizona, and a graduate certificate in science writing from the University of California, Santa Cruz. To find out what his latest project is, you can follow Michael on Twitter.

1 Comment Comment from the forums
  • rod
    "OSIRIS-REx's returned material will be stored and curated at NASA's Johnson Space Center (JSC) in Houston. The JSC team will oversee the distribution of the sample to researchers around the world, who will study it for a variety of purposes. One line of inquiry will focus on organic compounds, the carbon-containing building blocks of life as we know it. Scientists think carbon-rich asteroids like Bennu may have helped life get a foothold on Earth long ago, by delivering organics via impacts."

    Interesting thinking and report here. I compared to Charles Darwin letters of 1871 and 1882 for a look back in science on the topic of the origin of life.

    https://www.darwinproject.ac.uk/letter/?docId=letters/DCP-LETT-7471.xml
    https://www.darwinproject.ac.uk/letter/?docId=letters/DCP-LETT-13711.xml
    My note Charles Darwin hoped that someday evidence would be shown for life evolving from non-living matter but in his time, none was known that was *worth anything* and the *law of continuity* would provide this, also a general law of nature for abiogenesis. None of this in science is proven at present. There is no general law of abiogenesis seen operating in nature. So, here is a summary of four points in these letters that I learned.

    1. A warm little pond is postulated for the origin of life on Earth but Charles Darwin thought if abiogenesis operating in a warm little pond in his time, perhaps such life evolving from non-living matter would be quickly destroyed by existing life and eaten.

    2. No good evidence for abiogenesis taking place in Charles Darwin time seen in nature.

    3. The law of continuity is needed for abiogenesis to work apparently, and

    4. Someday a general law of nature developed to describe and show abiogenesis like other laws of nature, for example the laws of motion or law of gravity. Apparently all four I list here are missing in science today, even with natural law operating in nature in a uniform manner, i.e., *law of continuity*. When I consider point #1, it is good IMO to avoid catastrophism that wipes out abiogenesis creating life from non-living matter at the very beginning otherwise many abiogenesis events must be envisioned to replace the earlier efforts that failed. These are four points I learned by reading some of Charles Darwin letters on the warm little pond and origin of life on Earth.

    Now science reporting suggests to the public that there is overwhelming evidence for what Charles Darwin did not see as worthwhile evidence in his days, life evolves from non-living matter. Catastrophism invoked using asteroids to aid in creating life on Earth, something Charles Darwin did not use when discussing the *law of continuity* (no catastrophism at work). It will be interesting to read follow up reports on this asteroid material and see if the labs can demonstrate how catastrophic bombardment of asteroids on the early Earth gave rise to non-living matter that evolves into the first, living cell, complete with DNA and the ability to continue evolving and adding to the original body mass of life on Earth, without being wiped out.
    Reply