In 2010, in the waters of Mono Lake in California, NASA-funded scientists claimed to have found a microbe called GFAJ-1 they said rewrote biology. It had allegedly replaced the phosphorus in its DNA with the toxic element arsenic. The announcement, made at a high-profile press conference on December 2 that year, stunned the world.

The findings, soon published in the journal Science, hinted that life could rely on a radically different chemistry. Lead author and microbial geobiologist Felisa Wolfe-Simon declared, “Life as we know it may be due for a revision.”

Speculation surged: had NASA stumbled onto alien biology?

Set the ball rolling

On July 24 this year, Science announced that it would be retracting the GFAJ-1 paper, nearly 15 years after its splashy debut, citing shifting editorial standards and lingering public confusion.

“It’s important to have any groundbreaking work independently evaluated before drawing far-reaching conclusions,” University of Minnesota synthetic biologist Kate Adamala said. “We want the public to be excited, but the message must match the strength of the data.”

Mainstream media amplified the drama. One headline read: ‘NASA Discovers Life Not As We Know It’.

Ivan Oransky, co-founder of Retraction Watch, a site that tracks withdrawn papers and promotes research transparency, and executive director of The Centre for Scientific Integrity, saw the media blitz as pivotal. “Without the hype, this paper might never have been retracted.”

He pointed to NASA’s style of communication as a key factor in the storm that followed in 2010.

“Historically, NASA hasn’t always had a respectful relationship with journalists,” he said. “They’re great at promoting themselves, and sometimes at overselling.”

Peer review in public

To the people at large, the prospect of arsenic life hinted at alien biochemistry. But for many scientists, the GFAJ-1 paper raised more questions than answers. Critics began pointing out that arsenate is unstable in water, so its role in DNA seemed chemically implausible.

“If true, this would have overturned nearly a century of data, but nothing in the chemistry suggested it was possible,” Steven Benner, an early critic and chemistry professor at University of Florida said.

Others were initially intrigued. “I was very excited and impressed. It was a big deal in the origins community,” Adamala, then a graduate student, said.

But like many, her enthusiasm waned as flaws emerged. Microbiologist Rosemary Redfield became a leading critic and one of the first replicators to disprove the findings.

“It’s a fine example of how easy it is for scientists to be misled by an attractive hypothesis and of why we need both formal peer review and informal outside scrutiny.”

By late December, the backlash gained traction. Blogs and Twitter (now X.com) turned the paper into a case study on post-publication peer review.

Sheila Jasanoff, professor of science and technology studies at Harvard, noted that while such public spaces can foster valuable crowd-sourced peer review, they also risk overreach.

“These days science, like true crime, has spilled outside the constraints of officially authorised review. However, like all forms of democratisation, such informal policing can run out of control if it is driven by a mob mentality that is out to shame or undermine a researcher or a research program.”

The original team stood by their findings — but by now the tone had shifted.

Evidence falls apart

Over the next 18 months, multiple labs tested the paper’s core assertion.

In 2012, Science published two studies that refuted it. Redfield’s team found no arsenate in GFAJ-1’s DNA. Tobias Erb’s group confirmed the microbe still needed phosphorus to grow, i.e. it hadn’t rewritten biology, just tolerated low-phosphate conditions.

Wolfe-Simon maintained that her team’s methods showed arsenic was incorporated into DNA and were robust enough to rebut Benner’s contamination claims.

Science didn’t retract or flag the paper, saying claims should be resolved by further research, not editorial action. And since no fraud was alleged, the rebuttals sufficed.

“The whole debate ends up circling around the semantics of words like ‘error’, ‘fraud’, ‘misconduct,’” Oransky said. “But this paper, let’s be honest, has been understood as unreliable since at least 2012, if not earlier.”

Why science took so long

For Benner, the GFAJ-1 paper reflected differences in scientific perspectives. Biologists saw phosphorus as essential, chemists knew arsenate’s instability, geologists accepted mineral substitutions, and astrobiologists embraced radical possibilities.

“It wasn’t that reviewers were incompetent,” Benner said. “They just didn’t all speak the same scientific language.”

He saw another deeper flaw. NASA’s astrobiology community often relies on consensus panels that falter when no one challenges ideas outside their domain.

“Multidisciplinary science is essential,” he said, “but when it’s superficial, weak claims slip through. This wasn’t peer review breaking down: it was different communities assuming they shared standards while working from very different assumptions.”

Adamala echoed this concern: “Young scientists in interdisciplinary fields should embrace continuous peer review, as reliance on collaborators’ expertise can miss flaws that later scrutiny might catch.”

Correction sans closure

“They’re right to retract a paper whose high-profile conclusions were entirely wrong,” Redfield said.

One senior researcher noted that the Committee on Publication Ethics (COPE) guidelines, which many journals have adopted as a measure to improve research integrity, justify a retraction if the findings are unreliable. Here, multiple labs found phosphate in the arsenate medium, undermining the paper’s core claim that the microbe grew by substituting arsenic for phosphorus.

“The growth experiments at the heart of the paper were flawed,” the researchers said. “Even if it was an honest mistake, the core conclusions didn’t hold up.”

Adamala said that it’s a good example of self-regulation in science. “Slowly but surely, mistakes do get corrected.”

Oransky was more measured: “Science is now acting on an expanded definition of retraction that’s consistent with what’s been possible for a long time, but rarely used.”

Not everyone sees it as black and white. Jasanoff warned that retractions can erase the very messiness that makes science work.

“Rather than draw hard lines between truth and error, science advances through open debate,” she said. “It’s better to preserve a record that shows how scientists test, challenge, and refine their ideas, even when plausible claims later prove wrong.”

Benner, for his part, expressed worry that broadening retraction policies could weaken the informal scrutiny that exposed the paper’s flaws, raising questions about balancing error correction with preserving the scientific process.

Today, the whole saga has transformed into a cautionary tale. Adamala said the controversy may have cast a shadow over exotic chemistry research in astrobiology, making scientists more cautious about bold claims.

Who pays the price?

Wolfe-Simon’s rise and fall was swift. In 2010, she was hailed for a potential revolution in biology. Two years later, she quietly exited both NASA and mainstream science, her research career derailed by controversy and lack of funding.

“Good scientists would have responded by getting back into the lab and doing the necessary follow-up work. But these authors still don’t admit mistakes,” Redfield said, pointing to their rebuttal letter in response to the retraction.

Ariel Anbar, a coauthor of the now retracted paper, said, “Science cited no misconduct or specific mistake. We stand firmly by the integrity of our data.”

He also criticised the journal for not sharing a blog post it published regarding the retraction with the authors, calling it a breach of COPE guidelines.

Oransky disagreed: “What guideline is this referring to? Furthermore, standing by your data doesn’t mean there aren’t errors in it.”

Anbar also said the team rejected “the alleged error” and that it was raised in 2011 and rebutted in a peer-reviewed exchange.

“They may reject it,” Oransky replied, “but that seems to be the rationale for the retraction.”

Nonetheless, Oransky also said Science’s retraction notice could have been clearer. He explained that retractions often imply misconduct, so when Science called the paper unreliable but not unethical, it still put the authors on the defensive.

“You can see that here, they’re saying: ‘But there was no misconduct. No clear error.’”

Jasanoff said she doesn’t see it completely as an individual failure. She argued that the unusually long delay until retraction may reflect less a concern with scientific uncertainty and more with a broader institutional tendency to manage reputation, especially in an era of heightened fears over misinformation.

Wolfe-Simon’s arc underscored a stark truth: high-risk discoveries bring both acclaim and vulnerability. When science goes public, its failures play out just as visibly as its triumphs, leaving lasting questions about how to correct course without crushing the people behind the work.

A slow machine

Peer-reviewers cleared GFAJ-1 and media hype propelled it, but shifting editorial norms more than new data undid it 15 years later. Oransky singled out Science’s editor-in-chief, Holden Thorp, for leading that shift.

“Other journals have done it, but he’s been consistently engaged in a way that encourages open conversation, no matter whether people agree with specific decisions or not.”

That kind of editorial openness, he added, may be the real legacy of the arsenic life saga.

Jasanoff, however, cautioned that every retraction risks erasing the visible, iterative debate that builds trust. “It is better for people to understand that science moves through trial and error, and gradual self-correction. It is not a binary. All science is provisional.”

Benner drew a parallel to the 1976 Viking missions, where a premature “no organics, no life” verdict in Science stifled debate. “Calling the ballgame early had an unfortunate result. It prevented the dialectic the scientific process needs.”

The arsenic life case endures not because of its flawed claim, but for what it revealed about the pressures shaping modern science: how spectacular findings — especially from institutions like NASA — can short-circuit scrutiny, and how correcting course means confronting the very systems that made such claims irresistible in the first place.

Anirban Mukhopadhyay is a geneticist by training and science communicator from Delhi.

Renowned NASA filmmaker Simon Holland has claimed that Earth-based telescopes have detected signs of intelligent extraterrestrial life, with a potential announcement coming next month. Mr Holland, who has collaborated with the BBC and NASA-funded initiatives, asserted that an Oxford University-backed program dedicated to searching for extraterrestrial signals has made the groundbreaking discovery, the New York Post reported.

The filmmaker claimed that insiders from Mark Zuckerberg’s Breakthrough Listen project tipped him off that concrete evidence may be revealed within a month, possibly coinciding with the US election. This evidence might be linked to alien signals intercepted by the Parkes telescope in Australia, courtesy of researchers from the Oxford-based Breakthrough Listen initiative. 

“They found the evidence of a non-human technological signature a few years ago, using the Parkes telescope in Australia,” claimed Mr Holland.

The extraordinary claims have sparked a flurry of activity, with astronomers scrambling to gather evidence to substantiate the discovery. However, Simon Holland warns that a rival effort may be underway, suggesting that Chinese researchers might attempt to preempt the announcement.

”This is breaking news, as of yesterday, but the Chinese might be pipping them to the post, with their, FAST [Five-hundred-meter Aperture Spherical Telescope] program. It’s the largest telescope in the world since Arecibo,” Mr Holland told The Mirror.

Mr Holland further claimed that Chinese researchers are racing to publish findings on BLC-1 (Breakthrough Listen candidate 1), a promising signal detected by the Parkes Telescope in April 2019. BLC-1, emanating from Proxima Centauri, 4.2 light-years from Earth, is considered significant due to its single-point source origin, narrow band electromagnetic frequency (982 MHz) and Doppler shift, indicating a rotating planet.

Mr Holland believes this signal is unlikely to be human interference, as its characteristics are inconsistent with known natural phenomena. Breakthrough Listen has invested $100 million in telescope time to investigate five potential candidates, including BLC-1.

Dr Andrew Siemion from Berkeley’s Breakthrough Listen Science Program confirmed that researchers are still analysing BLC-1. If sufficient data confirms the signal’s technological origins, they will publish their findings. The Chinese are allegedly aware of BLC-1’s coordinates and may attempt to scoop the announcement. 

While this news is exciting, it’s essential to note that there’s currently no conclusive proof of extraterrestrial life. Astrobiologists have been studying the possibility of life beyond Earth, exploring extreme environments and chemically harsh ecosystems that could support life. The search for extraterrestrial life has been ongoing since the mid-20th century, with scientists using various methods to detect signs of life, including telescope data analysis and radio communications.

NASA has announced the first detection of possible biosignatures in a rock on the surface of Mars. The rock contains the first martian organic matter to be decisively detected by the Perseverance rover, as well as curious discoloured spots that could indicate the past activity of microorganisms.

Ken Farley, project scientist on the mission, has called this “the most puzzling, complex, and potentially important rock yet investigated by Perseverance”.

Perseverance is part of Mars 2020, the first mission since Viking that is explicitly designed to seek life on Mars (officially, to “search for potential evidence of past life using observations regarding habitability and preservation as a guide”). Arguably, that objective has now been achieved: potential evidence for past life has been found. But much more work is needed to test this interpretation of the data. Here’s what we do know.

Since landing in Jezero crater a few years ago, Perseverance has traversed a series of rocks formed nearly four billion years before present. Mars back then was far more habitable than the cold, dry, toxic red planet of today.

There were thousands of rivers and lakes, a thick atmosphere, and comfortable temperatures and chemical conditions for life. Many of the rocks in Jezero are sedimentary: mud, silt and sand dumped by a river flowing into a lake.

The new discovery concerns one of these rocks. Informally named “Cheyava Falls” (a waterfall in Arizona), it is a small reddish block of what looks like a mudstone, enriched with organic molecules. The rock is also laced with parallel white veins. Between the veins are millimetre-scale whitish spots with dark rims. For an astrobiologist, all these features are intriguing. Let’s take them one-by-one.

First, “organic molecules”, are made of carbon and hydrogen (commonly with sulphur, oxygen or nitrogen as well). Examples include the proteins, fats, sugars, and nucleic acids from which all life as we know it is constructed.

Organic matter is common in rocks on the earth, most of it derived from the remains of ancient organisms. But the term “organic” is slightly misleading: such molecules can also be produced by non-biological reactions (in fact, we know this was happening four billion years ago on Mars).

Simple non-biological organic molecules are common in the universe, and NASA’s Curiosity rover already found them in mudstones in Gale Crater. They were also reportedly detected by Perseverance in Jezero crater last year.

Nevertheless, Ken Farley considers the new observation the first truly “compelling detection” of organics made by Perseverance. NASA has not told us which types of organic molecules are actually present in Cheyava Falls, so it is hard to evaluate their origins. They could turn out to be biological, but a full analysis using laboratories on the earth would be needed to settle this question.

Next, the veins. These are composed of calcium sulphate, which precipitated like limescale when liquid water ran along fractures in the subsurface. Veins like these are common in Martian sedimentary rocks (Curiosity saw plenty of them), and of course they are not “biosignatures” even though they normally represent habitable conditions.

My own work has shown that microorganisms inhabiting subsurface fractures can produce chemical fossils that get trapped in calcium sulphate veins. Strangely, however, the veins in Cheyava Falls also contain olivine, an igneous mineral. This might suggest that the water was injected at temperatures too high for life. We need more data to know one way or the other.

Finally, what about those whitish, discoloured spots? These look like the “reduction spots”, also called “leopard spots”, commonly seen in red sedimentary rocks on the earth. Such rocks are rusty-red because they contain an oxidised form of iron. When chemical reactions modify the iron to a less oxidised state, it becomes soluble. Water carries the pigment away leaving a bleached spot behind.

On the earth, these reactions are often driven by subsurface-dwelling bacteria. They use the oxidised iron as a source of energy, just as you and I use oxygen in the air. On Mars, bacteria-like organisms could have used the organic matter in the rock to complete the reaction (just as we use glucose from the food we eat).

Reduction spots haven’t been seen before on Mars, although bleached linear “halos” observed by Curiosity in Gale crater are somewhat similar. As one of the few astrobiologists to have studied reduction spots on the earth – and found evidence for biological processes within them – I am personally delighted. But as ever, caution is needed.

Potential non-biological causes need to be explored and ruled out. Iron-dissolving reactions can and do happen in sedimentary rocks without life. The dark margins of the Cheyava Falls spots are enriched in both iron and phosphate, an association previously suggested to occur around some calcium sulphate veins on Mars. This observation is consistent with life, but also with chemical reactions driven by acidic fluids.

The new findings will nevertheless embolden those calling on NASA and the European Space Agency to proceed with the troubled multi-billion-dollar sample retrieval programme, which Perseverance was supposed to begin. The rover has now cored out a piece of the Cheyava Falls rock. If current plans are realised – a big if – then future spacecraft will collect this piece (and others) and bring it to the earth.

It will then be analysed in state-of-the-art laboratories far more capable than the instruments aboard Perseverance. Until that happens, we cannot be sure whether Perseverance has really found fossils of ancient life on Mars. The evidence so far is not definitive, but it is certainly tantalising.

Sean McMahon is reader in astrobiology, University of Edinburgh. This article is republished from The Conversation.