On Sept. 30, NASA formally concluded OSIRIS-REx, the historic first U.S. mission to pluck a pristine piece of an asteroid and deliver it safely back to Earth.

The van-sized OSIRIS-REx spacecraft — whose name is short for Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer — visited and sampled Bennu, an ancient space rock holding pristine remnants from the dawn of our solar system more than 4.5 billion years ago. Among those cosmic relics are raw organic building blocks, the kind that may have seeded life on Earth.

"I have known this day was coming for a long time, but it is still difficult to see it arrive," OSIRIS-REx Principal Investigator Dante Lauretta, who's based at the University of Arizona, said in a post on LinkedIn. "I feel enormous pride in what we accomplished together, and real sadness that this journey has come to an end."

For the mission team, the farewell capped a decade of high-stakes engineering, on-the-fly troubleshooting and nail-biting close calls that ultimately delivered to Earth the largest asteroid sample ever collected in space, one that held secrets from the early solar system.

Long before launch, the team faced obstacles that nearly thwarted the endeavor — chiefly, two rejections from NASA — before finally securing the green light for the $1 billion project under the New Frontiers Program in 2011.

When OSIRIS-REx launched on Sept. 8, 2016, on a two-year journey across the inner solar system, Bennu was little more than a point of light in telescopes. Scientists expected the asteroid’s surface to be a smooth, sandy sphere where OSIRIS-REx could seamlessly touch down. Much to their surprise, however, when the probe arrived at the asteroid in late 2018, it revealed Bennu to be a treacherous, loosely bound amalgamation of jagged boulders.

"Our expectations about the asteroid's surface were completely wrong," Lauretta said in an Oct. 7 statement from the University of Arizona. "There was no obvious place to collect a sample anywhere."

When OSIRIS-REx touched down on a small crater named Nightingale, Bennu offered so little structural resistance that scientists said its surface reacted more like fluid than a hard, rocky shell. The spacecraft's sampling head sank directly into the asteroid, stopping after burrowing 20 inches (51 centimeters) deep by firing its thrusters at the right time to pull away, with the precious sample in hand.

Then came another nail-biting moment: The sample collector lid got jammed in a partially open position because so much material was scooped up, allowing fragments of the precious cargo to escape. In a race against time to prevent further loss, the mission team quickly stowed the sampler head directly inside the return capsule, securing the cosmic treasure for its journey back to Earth.

Even the final return to Earth, on Sept. 24, 2023, kept the team on edge: A parachute failed to deploy properly during reentry, forcing a tense but ultimately safe landing in the Utah desert.

"Successful exploration missions are not those that avoid surprises; they are those that are deliberately designed to adapt to them," Lauretta said in the statement, quoting a line from the mission's final report to NASA.

"That certainly describes OSIRIS-REx," he said. "Again and again, the mission presented us with circumstances we had not expected, and again and again, this team found a way forward."

The mission's triumphs began long before the samples reached Earth. For example, the probe set a Guinness World Record when it slid into orbit around the 1,610-foot-wide (490 meters) Bennu, which became the smallest object ever circled by a spacecraft.

The scientific payoff that followed included remote-sensing work that confirmed Bennu's surface is coated in carbon-bearing compounds. Those observations also revealed that Bennu was once part of a much larger, water-rich parent asteroid that shattered in a catastrophic collision in the main asteroid belt between Mars and Jupiter.

The returned sample — which weighs 4.29 ounces (121.6 grams) here on Earth, more than twice the mission's requirement — continues to thrill and occupy scientists.

A wave of research papers, now topping 200, continues to piece together the composition and history of the ancient space rock. Among other findings, Bennu's pristine material has revealed amino acids and sugars that, on Earth, are essential for life, alongside a history of exposure to liquid water that could have served as the "broth" for these compounds to interact.

More discoveries are likely to come. Most of the returned Bennu sample is being preserved for future generations of scientists, who will study it "with questions and instruments we cannot yet anticipate," Lauretta said in the statement.

Though its OSIRIS-REx chapter is closed, the spacecraft itself is far from retired. Renamed OSIRIS-APEX (OSIRIS-APophis EXplorer), the probe is using its remaining propellant to head toward Apophis, another near-Earth asteroid and a different type of space rock from Bennu. It is scheduled to arrive in 2029.

Astronomers estimate that our home galaxy, the Milky Way, has churned out more than 10 million black holes over its 13-billion-year history. Yet so far, they have found only 70.

Now, a group of astronomers in the U.K. is trying to close that vast gap by enlisting the public. Their project, called Black Hole Hunters, is looking for volunteers with a computer and a few spare minutes to sift through troves of data gathered by a NASA space telescope. By flagging recognizable patterns that could point to a "missing" black hole, volunteers can help fast-track a search that would otherwise take years, the team says.

"You'll be narrowing down precisely where we need to point our telescopes next," project co-lead Adam McMaster, an astronomer at the University of Southampton in the U.K., said in a statement, "and you might be the one to discover a black hole."

Cosmic magnifying glasses

Black holes form when massive stars roughly 20 times heavier than our sun run out of fuel and collapse, leaving behind an abyss with gravity so immense that even light cannot escape. While invisible themselves, these cosmic behemoths reveal their presence by bending the light of nearby objects, and the Black Hole Hunters project is searching for one specific manifestation of this effect.

It happens thanks to the fact that massive stars often form in pairs, and a star can sometimes survive the violent supernova explosion that turns its companion into a black hole. When that happens, the two bodies continue to orbit each other. If such a duo aligns just right with Earth, the black hole will periodically pass directly between its companion star and our planet. And when it does, the black hole's gravity acts like a cosmic magnifying glass, bending and magnifying the star's light, causing it to briefly appear brighter to watchful telescopes.

To find these hidden giants, the project relies on data from NASA's Transiting Exoplanet Survey Satellite, or TESS. Although the satellite's primary mission is to hunt for planets beyond our solar system, its method of data collection — tracking tiny, continuous changes in a star's brightness over time — is ideally suited for identifying black hole magnification events, the project description notes.

"It's a simple task with no expertise required," McMaster said in the statement. "We will show volunteers examples of what to look for so all they have to do is recognise the right patterns."

Automated algorithms conduct a preliminary sweep of the TESS data, screening millions of potential stars for the most obvious black hole candidate locations, according to the project description. But, the researchers say, artificial intelligence struggles with the messy realities of the cosmos, such as stellar flares and the natural pulsations of stars that can trick the algorithms into false positives.

The human touch

That makes human volunteers a key part of the search. To keep errors in check, each graph is shown to multiple volunteers, and their answers are combined so that individual mistakes average out, according to the project's website.

"I can search for black holes on my laptop from my bedroom — and could make a real impact on real space science," Grace Clarke, an undergraduate student of physics and astronomy at the University of Southampton who's involved with the project, said in the same statement. "The data's easy to understand — it's just pattern recognition — and you don't need a degree in astronomy to read it."

The crowdsourced shortlist of promising signals lets astronomers aim follow-up observations at specific stars, such as precise measurements of whether a star is being tugged at by an unseen companion. Those measurements take time and are expensive, so a good shortlist helps researchers spend scarce telescope time wisely, the team says.

Since launching on the Zooniverse platform in October 2021, the project has attracted nearly 23,000 volunteers, who have completed more than 12 million classifications, according to its website.

Before turning to TESS, the team ran a similar search using data from SuperWASP, a ground-based survey that, like TESS, monitored stars for signs of planets from 2004 to 2016. Those results are still being analyzed and are expected to be published soon.

The team also plans to widen its search with observations from other instruments, including the European Space Agency's Euclid mission and NASA's recently launched Nancy Grace Roman Space Telescope.

"With potentially thousands of new discoveries, we need all the help we can get," McMaster said in the statement.