It came from Mars and crashed into Antarctica.
Its journey from the red planet to the frozen plains was a long one. About 17 million years ago, a monster rock collided with Mars, punching a hole in its side and jettisoning planetary debris across the solar system. The wreckage raced away at more than 3 miles per second, escaping the planet's gravitational pull and fleeing into the cosmos.
Then, some 13,000 years ago, a piece of that wreckage landed near a Y-shaped ridge in the Transantarctic Mountains known as Allan Hills. The area, draped in layers of snow, has been dubbed "meteorite heaven" by planetary scientists because the flowing ice sheet of East Antarctica butts up against the mountain range, forming a natural collection area for space rocks.
Nowhere else on the planet has provided a bounty of otherworldly riches like the desolate, frozen plains of the Antarctic. More than 22,000 space rocks have been found on the continent, offering scientists a way to study the formation of our solar system. But the wreckage discovered in Allan Hills has become the Antarctic's most famous.
"The major legacy of that rock is that it basically drives a huge amount of what is happening in planetary science," says Gretchen Benedix, an astrogeologist at Curtin University in Western Australia.
The potato-size chunk, dubbed ALH84001, had rested on the ridge's surface untouched for millennia until it was finally discovered by Roberta Score, a member of the Antarctic Search for Meteorites (Ansmet), on Dec. 27, 1984. Nine years later, a team of NASA scientists determined the rock was of Martian origin, showing evidence it came from the planet's formative era some 4 billion years ago when water existed on its surface.
The rock sparked a revolution in astrobiology — the hunt for life outside of Earth — that is still felt today as NASA's Perseverance rover rolls around the surface of Mars. It gave scientists a tangible route to answering one of the biggest questions of all: Does life exist elsewhere in the cosmos?
The first tentative answers came when scientists at NASA's Johnson Space Center cracked open the rock from Antarctica in 1996.
Cracking open ALH84001 is like opening a portal to a planet more than 140 million miles away.
Many research teams had done so since its discovery, but it's NASA geologist David McKay whose name is forever linked to the Martian chunk. McKay had worked on the Apollo moon program, studying lunar dust, and was well-versed in studying samples from other worlds.
His team of scientists at Johnson went to work examining ALH84001's chemical components in the early '90s, hoping to reveal what was happening on the red planet 4 billion years ago. In studying the rock, the team uncovered carbonate minerals and unusual, wormlike microstructures within.
They reasoned the worms could be fossilized nanobacteria — evidence of alien life.
Days before McKay's team published its work in the journal Science, US President Bill Clinton fronted a media throng on the South Lawn at the White House, revealing this world-changing hypothesis. "If this discovery is confirmed," Clinton said, "it will surely be one of the most stunning insights into our universe that science has ever uncovered."
While the headlines of the day shouted that scientists had found "evidence of primitive life on early Mars," the scientists themselves were a little more tempered.
At the time, Everett Gibson, a planetary scientist at JSC and co-author of the paper, said the team was "putting this evidence out to the scientific community for other investigators to verify, enhance, attack — disprove if they can — as part of the scientific process." Gibson hoped "within a year or two" the questions would be resolved, but the hypothesis was immediately controversial. Other groups did exactly as asked: attacked, questioned, enhanced and, ultimately, disproved many of the claims made in the paper.
Over 20 years later, few serious planetary scientists believe ALH84001 contains life from another planet. But the meteorite focused efforts in astrobiology and saw organizations like NASA double down on investigating Mars.
Ralph Harvey was making the 1,200-mile journey from Houston to his mother's house in Wisconsin just as Clinton announced the discovery of potential Martian life in ALH84001 in 1996.
Harvey, a geologist who'd only just finished studying samples of the meteorite, had recently completed a stint at NASA's JSC and, four weeks earlier, published a paper trying to explain some of ALH84001's unusual features. Harvey and co-author Harry McSween Jr. hypothesized that the carbonates found within the meteorite may have formed as a result of high temperatures on ancient Mars.
The pair's conclusions hadn't garnered a lot of interest from the press, but by the time Harvey reached his parent's house, his mother told him the phone had been ringing off the hook. CNN wanted to talk. So did CBS. Newsweek. The list went on. He quickly learned that McKay and other scientists in the same building at JSC — some he had shared a wall with — were claiming fossils existed in ALH84001. Harvey's earlier paper put him at the top of the list of experts to call.
Harvey took over the Ansmet project in 1996, leading the hunt for meteorites in Antarctica around the time ALH84001 captivated the world. It put the Antarctic hunt for meteorites on the map.
Although only about a fifth of the world's meteorites fall over the poles, Antarctica has natural advantages that make it a prime position for finding otherworldly rocks. "If you want to find things that fall from space, lay out a big white sheet," laughs Harvey. "Antarctica is a big white sheet 3,000 kilometers across."
Ansmet has been continuously funded by the US National Science foundation, with its first expeditions stretching back to 1976. It has helped discover more than 22,000 meteorites in the Antarctic, with most originating from asteroids or the moon. Expeditions south helped discover the first lunar meteorite on Earth and the first Martian meteorite, ALH77005. But its most famous rock remains ALH84001.
Harvey says there's no evidence for Martian life lurking in the meteorite. He opposed the interpretation from McKay's group in 1996 and says he became "the poster child" for a "dead Mars" — one that was too hostile for life to thrive. He's spent many years trying to understand ALH84001 but notes he's moved on to other things. "I got sick of that rock," he laughs.
Even without signs of alien life, Harvey notes it's an amazing rock that tells an elegant story and highlights the importance of Ansmet's searches on the frozen continent. Those searches could be under threat. For one, some parts of Antarctica are warming faster than anywhere else on the planet. Harvey hesitates to predict any specific ways climate change could hinder the hunt for meteorites finds but allows that it will "certainly have an effect." It may be that a warmer climate provides a bigger area to find the rocks, for instance, but equally, the new areas might flow more rapidly, causing rocks to be lost.
There's also the issue of funding. Ansmet had been funded by the National Science Foundation since 1980, with support from both NASA and the Smithsonian Institution. But in 2013, it ended its support, and NASA took over. In 2016, the three agencies signed a new agreement that would see NASA fund the work while the NSF provided support for scientists to get out in the field and collect the rocks. However, Harvey says, this support has been dropped for the 2022 season. It's unclear why.
After two pandemic-affected years curtailed fieldwork, the fate of Ansmet's field work hangs in the balance.
Given that half a century since ALH84001's discovery it's still being poked and prodded, analyzed and examined, painting a picture of the ancient chemistry and climate evolution of Mars, there's concern that the about-face practically shuts down one of the most lucrative portals to the red planet.
CNET contacted the NSF but did not receive a response by time of publication.
After ALH84001 made worldwide headlines in 1996, planetary scientist Andrew Steele knew he had to see the rock.
At the time, Steele had been working with bacteria, imaging the organisms using a technique known as atomic force microscopy, which allows scientists to see into the nanoworld and witness, for instance, the microscopic structures on a bacterial membrane. He turned his attention to ALH84001 not long after its discovery. "Dave [McKay] sent me a piece, and we went to work scanning it for signs of bacteria," Steele recalls.
One of the major claims in the 1996 paper revolved around the existence of thin, wormlike structures found in ALH84001. McKay's team described these as nanofossils — evidence of incredibly small bacteria. Steele's microscopy technique could help shine more light on what the structures might be. The features captivated the imagination of the media and came under the most scrutiny when the results were first published. (Harvey co-authored a paper directly opposing the nanofossil hypothesis in 1997.)
Over the next decade, hundreds of papers attempted to explain those features via chemical analysis, computer modeling and comparisons with other meteorites. Steele himself published a paper in 1998, detailing the results of his atomic force microscopy technique, suggesting some of the features may have arisen from the special coating NASA had used to study ALH84001.
Unlike Harvey, he hasn't got sick of studying the rock.
In January 2022, Steele, now working at the Carnegie Institution for Science, and his team published new data about ALH84001 in the journal Science. The team examined small pieces of ALH84001, which is still housed at JSC, revealing some of the natural processes that gave rise to organic compounds on Mars. Organic compounds are those containing carbon and are the building blocks of life, at least as we know it.
Studying minerals present in ALH84001, the team was able to describe the chemical reactions taking place on Mars, in the presence of water, 4 billion years ago. Ultimately, the team concluded that organic molecules in the rock could have been generated on Mars without invoking aliens as their source.
Steele notes that his latest paper isn't a critique of the life hypothesis presented by McKay and colleagues. Rather, it shows that on early Mars organic molecules were being produced — the type of stuff that might, under the right conditions, give rise to life. And the results aren't relevant just to Mars, but anywhere that volcanic lava flows comes into contact with salty water. All that, from a rock collected from Antarctica nearly 50 years ago.
It's unlikely McKay and the other scientists at NASA could have predicted the kind of legacy their 1996 paper would leave.
"Science is about posing and testing hypotheses, and this paper started a journey that has led to a much greater understanding of our solar system, the science of life detection and what life could be on another planet," Steele says.
Steele's latter two points are perhaps the most important. When scientists went looking for life in ALH84001, we were hoping to see alien microbes staring back at us that resembled life as we know it. But life on other planets could be entirely different from life on Earth, utilizing different chemicals and different ways to replicate. We simply can't say. It might even force us to rewrite the idea of "life" in general. What is life?
Even if we can't answer those deep, philosophical questions with a rock like ALH84001, we might be able to do so if we can get samples directly from the surface of Mars. That's exactly what NASA plans to do with the Perseverance rover, which landed on the red planet in February 2021.
"The prospect of being able to study samples collected directly from the surface of Mars is a game changer," says Aaron Cavosie, a planetary scientist at Curtin University in Australia.
Today, Perseverance is rolling around an ancient Martian crater known as Jezero, once home to a huge lake. The rover is equipped with a suite of instruments for drilling into rocks and caching samples in titanium capsules. The collection part is, in some ways, the easy bit. Since September, the rover has been collecting samples and storing them in its mechanical stomach.
Getting them home is a whole different problem, however. Within the next decade, NASA hopes the rover will regurgitate those capsules onto the Martian surface and another rover, yet to be built, will pick them up, ferry them to a rocket and launch them back to Earth in the early 2030s. That means "the first scientists to open capsules delivered directly from Mars are currently sitting in high school classrooms," says Cavosie.
It's important to note how this compares with Ansmet's work in Antarctica, given the current unclear state of funding for the project. Ansmet's work only requires a fraction of the cost that the $2.7 billion Perseverance mission will accrue over its lifetime — and that's not factoring in the cost of building and sending the retrieval rover, either.
Provided the samples are returned to Earth successfully, planetary scientists will have access to the most pristine Martian rocks in history. If we're talking about windows to the past, these samples are more like time machines that not only let you see what ancient Mars was like, but to understand it, to feel it as it has been for eons. "If you can pick it up yourself," notes Benedix, the planetary scientist from Curtin University, "you have a lot more information, you have context."
Those future humans, meticulously poking and prodding pieces of rock from a dried-out lakebed, will be the first to study pristine samples from another planet. They will be attempting to answer the same question posed to McKay and his team. A question posed long ago, when we first began to look toward the stars. It's one of the biggest questions of all: Are we alone?
Answering that question will solidify the legacy of the search for meteorites in Antarctica and of ALH84001, the unassuming potato rock that supercharged our pursuit of life beyond Earth.