Signs of water, carbon revealed in first results from sample of asteroid Bennu

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Two weeks after cracking open a capsule bearing a sample from a distant asteroid, scientists with NASA’s OSIRIS-REx mission are ready to reveal what they have learned.

Among their initial findings: Material from the asteroid known as Bennu is 5 per cent carbon by weight. It also contains clay-like minerals that could only have formed in the presence of water, a sign of the crucial role that similar asteroids may have once played during Earth’s formation.

“Already this is scientific treasure,” Dante Lauretta, the mission’s principal investigator, said during a Wednesday news briefing at the Johnson Space Center in Houston, Tex., where researchers have been examining the sample.

“The reason that we have oceans and lakes and rivers and rain is because these clay minerals, like the ones we’re seeing from Bennu, landed on Earth four billion years ago to 4.5 billion years ago, making our world habitable.”

The results are based on an analysis of the first portion of the sample that scientists encountered. It consists of a spoonful of dark dust that was found scattered along the inner edge of a lid that protected the sample container.

But there is clearly more to come.

At the briefing, Dr. Lauretta presented a photo of coal-black material sitting atop the TAGSAM head – a Frisbee-sized component that carries the bulk of the sample. The device was plunged into the surface of Bennu three years ago and was stowed inside the capsule for its return flight.

The photo shows that a centimetre-long asteroid fragment has become lodged in the circular flap that would otherwise be closed, allowing a portion of the sample to spill out.

By itself, the amount that is visible could be the largest trove of extraterrestrial material ever returned from beyond the moon’s orbit. Scientists have yet to open the device to see how much more lies inside.

“With this abundance we’re taking our time, methodically processing to properly care for every valuable piece of Bennu,” said Eileen Stansbery, the space centre’s chief scientist.

Canada is a partner in the US$1.6-billion mission and is slated to receive a 4-per-cent share of the capsule’s contents. The larger the total amount, the more the country will receive for current and future generations of scientists.

“Visually there is a lot of material to work on. It’s quite a relief and very exciting,” said Kim Tait, the senior curator of mineralogy at the Royal Ontario Museum in Toronto, who will aid in selecting Canada’s part of the sample.

Dr. Tait added that she is intrigued by the range of sizes in the material. While carbon-rich asteroids are generally thought to consist of fairly light and friable material, the larger pieces in the sample may indicate the presence of something that is structurally stiffer.

During the briefing, Dr. Lauretta echoed that observation: “One of our key hypotheses is that there’s two major different kinds of rocks on the surface of the asteroid – darker and brighter, weaker and stronger. And we may see those already represented and in the material that leaked out of the TAGSAM.”

Caroline-Emmanuelle Morisset, a program scientist with the Canadian Space Agency, said the country’s sample will aim to reflect that variety, in part to provide a more complete picture of the asteroid’s evolution. For example, some of the larger pieces can be sectioned and may reveal minerals in one form were altered in other parts of the sample by the presence of water.

Whatever Canada receives, it will not arrive before the end of next year, Dr. Morisset said. That is the earliest that a clean room for storing and working with the sample can be completed at the agency’s headquarters near Montreal.

Last week, the agency announced that the contract for building the clean room has been awarded to the Montreal-based engineering firm Teknema Inc.

OSIRIS-REx was launched in 2016 and arrived at Bennu just over two years later. The tiny asteroid, which measures about 500 metres across, was selected as a target because its chemical properties suggest it is a relic from the solar system’s formation.

After an extensive period of remote sensing using cameras and a Canadian-built laser scanner, a site was selected where the spacecraft could approach the 500-metre-wide asteroid and touch its surface with an outstretched sample collection tool.

After the manoeuvre, mission scientists estimated that the spacecraft may have captured anywhere from 100 to 350 grams of material, but the true amount will not be known until the TAGSAM head is opened and fully emptied of its contents. When the OSIRIS-REx was planned, a 60-gram sample was the bar set for mission success.

In 2020, Japan’s Hayabusa 2 mission brought back 5.4 grams of material from another asteroid called Ryugu. Ann Nguyen, a co-investigator on the OSIRIS-REx mission who has previously studied isotopes in that asteroid’s sample, said she is eager to compare those results with what she learns from Bennu. The result may help clarify where different elements within the asteroid originated.

“You can really do a lot of science with just a little bit of material,” Dr. Nguyen said. “When we saw the larger particles, I just felt like I could analyze that for the rest of my life.”