Latest news with #NikkuMadhusudhan
Yahoo
20 hours ago
- General
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Does extraterrestrial life smell like the sea?
Dimethyl sulfide, also known as DMS, sounds like it could be a chemical compound you'd try to avoid on an ingredient label, or the poisonous ingredient in a murder mystery. But some scientists view this simple compound as a biosignature — a key indicator of life. So there was great excitement when DMS was discovered on a "sub-Neptune planet" far from our solar system – 124 light years away, or about 17 trillion miles, in the constellation Leo. 'We want to be a bit careful in claiming any evidence of life at this stage,' cautioned lead author Nikku Madhusudhan, of Cambridge University, about the findings he published last month in The Astrophysical Journal Letters, a publication of the American Astronomical Society, with other researchers from two American space institutes and two British physics and astronomy departments. 'We have to look at a lot more molecules, and we have, and we couldn't come up with a much better explanation,' Madhusudhan told Salon in a video interview. He admits he can't be 100% certain that dimethyl sulfide, or (CH3)2S, exists on the planet called K2-18 b. But it looks very likely, as last month's research built on a paper published in 2023 that also found suggestions of DMS on the same planet but relied on different evidence. But why would a random compound detected on a planet so far beyond our reach be a strong indicator of life? Well, let's consider the story of DMS on Earth, a story of the strange and poetic ways life appears and reappears in different guises — and with different scents. Dimethyl sulfide is the largest natural source of atmospheric sulfur on Earth, which means that it gets into the atmosphere and cycles around. But it starts its journey in the ocean. You're absolutely familiar with DMS, even if you've never heard of it before. It's the source of the smell of the sea, that sort of fishy, sort of eggy aroma that evokes deeply nostalgic reactions in, well, almost everyone. Interesting pushback came from Christophe Laudamiel, a master perfumer at Generation by Osmo. 'I have personally never used that ingredient for the smell of the sea,' he told Salon by email. 'It would be rather used for 'hot' smells and for ripe to overripe smells." He compared the odor of DMS to "fish that stayed too long in the sun," adding, quite understandably, that "we usually avoid" such associations "when we recreate the smell of the sea in perfumery." Rather than relying on those fish-rotting-in-sun odors to get ocean-smelling perfume, suggested Generation by Osmo founder and CEO Alex Wiltschow (also by email), "We combine aquatic notes with mineral wet stone notes, salty notes and clean air notes," along with, perhaps, "a touch of seaweed absolute as well or mossy top notes." Similarly environment-evoking are the substances geosmin and petrichor. Petrichor is the pleasant, earthy aroma of rain falling on dry soil, sometimes described more simply as the smell of rain. That word has almost become trendy. In fact its use appears to have skyrocketed in the past quarter-century, though it was coined in the journal Nature in 1964. Like geosmin, the substance that gives earth its characteristic "earthy" odor, petrichor remains close to the ground. Dimethyl sulfide, however, gets around. The DMS that cycles around our world is produced, for the most part, by marine organisms, most notably the microscopic plants known as phytoplankton that live in the nutrient-rich upper layer of the ocean. These tiny organism exist in abundance, which is why DMS is responsible for most of that smell we associate with the seaside. From the surface layer of the Earth's oceans, DMS, which is a volatile chemical, escapes into the air, joining the atmospheric cycling of sulfur. As one researcher describes this process, once in the atmosphere DMS "has other major effects, being the 'seed' that sets off cloud formation over the oceans. Indeed, the production of this molecule is on such a scale that it has major effects on the world's climate, thanks to its effect on the cloud cover over the oceans.' That quotation is nearly 20 years old, but scientists still don't know exactly to what extent DMS is responsible for seeding clouds, just that it's a significant factor. The tiny aerosol particles formed when DMS molecules are zapped by sunlight and other molecules in the atmosphere, which become the 'seeds' for clouds, also exert meaningful effects on our climate by reflecting sunlight back into space. In 2007, scientists at the University of East Anglia discovered that a single gene could produce dimethyl sulfide from dimethylsulfoniopropionate, or DMSP, the food that phytoplankton eat. As described in a paper in Science, you can take that gene, which has the catchy name dddD, from bacteria that live in the sea, or find it in other species of bacteria that hang out with plants instead but also produce DMS. Once you've found a bacterium with the dddD gene, you can clone it and stick it into an bacterium, which will then happily produce dimethyl sulfide. The aforementioned predecessor chemical DMSP is found, by the billions of tons, all over the world's oceans, seas and seashores. Marine plants and phytoplankton use it to protect themselves from the saltiness of seawater, literally as a buffer against stress. When these tiny plants die, some of their DMSP becomes available, as food for other bacteria. Terrestrial plants may also have symbiotic bacteria living in their root systems, which produce dimethyl sulfide from the DMSP released when their hosts die. This process — one kind of organism dies, offering sustenance to others — is how this cycle begins, at least on Earth. (If you can actually say that a cycle has a beginning or an end.) As one of the East Anglia scientists, Andrew Johnston, wrote in a 2007 project funding proposal, describing the role of DMS in seeding clouds, its importance has been known since 1971, "with some 30 million tons of it being liberated into the air, worldwide, every year.' Aquatic bird species such as sea petrels and shearwaters are attracted to the ripe-fish aroma, while Johnston later discovered that the Atlantic herring has strains of bacteria in its gut microbiome called Pseudomonas and Psychrobacter, which digest DMSP and break it down into, yes, dimethyl sulfide. How did those bacteria get inside a fish? Herring eat small plants known as mesozooplankton, which themselves eat the much smaller phytoplankton. This familiar ecological pattern — bigger creatures eating smaller creature — has internalized the production of this evocative and volatile to the food chain, it seems, the creation dimethyl sulfide can take place not just in the surface layer of the ocean, but inside herring guts as well. Herrings are vertebrates, in the greater evolutionary scheme not all that different from us. Does this mean that humans also have the potential to create sulfurous stinks from our own insides? Well, there's no evidence at this point that our microbiomes contain DMS-producing bacteria. But that's ok. As you may be aware, our species can produce our own glorious forms of stink. Dimethyl sulfide is an essential element in the characteristic odors of blood, serum, tissues, urine and breath in people (and rats). Not to mention the distinctive smell of feces and flatus, i.e., farts. Let's mention here that dimethyl sulfide is emitted during wildfires, and so contributes to a scent that has grown chillingly familiar in many parts of North America in recent years. It's also largely responsible for the smell of the delicately-named dead horse arum, a relative of the so-called corpse flower, or titan arum. Other flowers with unappetizing odors use different chemicals as their top notes, all with the purpose of attracting pollinators drawn to the aroma of their preferred type of rotting meat. Here for example is Wikipedia's almost lyrical rundown of the various sources of the corpse flower's scent: 'Analyses of chemicals released by the spadix show the stench includes dimethyl trisulfide (like limburger cheese), dimethyl disulfide (garlic), trimethylamine (rotting fish), isovaleric acid (sweaty socks), benzyl alcohol (sweet floral scent), phenol (like Chloraseptic), and indole (like feces).' Scientists comparing the molecules involved in producing the stench of dead horse arum with those produced by a rotting corpse found that dimethyl sulfide was associated with the middle stage of decomposition in actual corpses (to be clear, this involved dead mice, not dead horses or human cadavers). All this odoriferous research has convinced some scientists that DMS is intimately associated with life, making it an ideal biosignature if found hundreds of light years away on some lonely planet. Critics of Madhusudhan's findings point out, however, that dimethyl sulfide can exist without demonstrating life at all. For one thing, you can make it in a lab. As the perfumer Laudamiel told Salon, DMS is "often used in perfumery, but not for its low-tide, rotten egg facet.' The human nose can detect one part per million of DMS, as an unpleasant, cabbage-like smell used, for example, to add a warning signal to the poisonous gas carbon monoxide, which is otherwise odorless natural gas. DMS also results from kraft pulping, producing a ghastly, retch-inducing smell you'll have noticed if you've ever driven by a paper processing plant. It's produced naturally as bacteria do their work on dimethyl sulfoxide waste in sewers. When it's not saving us from asphyxiation or carrying out useful industrial processes, dimethyl sulfide also lends its "low-tide, rotten egg facet" as a nearly subconscious flavor in food and drinks, measured in a few parts per million. In brewing certain lagers, though, breweries may want that slightly funky flavor, and add enough DMS to cross the flavor threshold as a hint of the ocean (or of distant rotten eggs, or cabbage). The natural production of DMS is also medically useful. It turns out that as a kind of bacteria turns from existing peacefully in our mouths to causing colon cancer in our nether regions, it produces dimethyl sulfide. Worsening osteoporosis in older women may lead to exhaling DMS, as can the positive effects of a medication cocktail for children with cystic fibrosis. But how is it that the compound that gives us the glorious smell of the sea — and just perhaps, our first evidence of life on a distant planet — also provides the generally disagreeable fragrance of flatus, feces and flowers that smell like rotting meat? 'It works just like salt in a cake," explained Laudamiel. "In combination with other molecules, at low, unrecognizable dosages, it brings out the flavors of other facets." Unpleasant-sounding flavor notes such as "the overripe 'vomity' note found naturally in papaya ... the 'feet' note found in Parmigiano or the 'sweaty' note found naturally in dark chocolate" produce magical effects in combination with others and in just the right amount. Remove those notes, he concluded, and your papaya, cheese or chocolate will "taste much less yummy." Indeed, DMS, provided by nature at just the right dosage, is a component in the much coveted scent of truffles. Turning away from our planet with its stinky-feet cheese, vomity papayas and sweaty chocolate, and turning to the stars, DMS is used as an additive in rocket fuel, added to ethylene oxide to prevent exhaust nozzles getting dirty and stop carbon building up on firing-chamber surfaces. But no existing or planned spacecraft can get us anywhere near the next possible known source of dimethyl sulfide on K2-18 b, the planet where Madhusudhan and colleagues have found, thanks to the James Webb Space Telescope, what they think could well be this signature of life. Astronomers these days are really interested in sub-Neptune planets, meaning those with diameters larger than Earth but smaller than Neptune. It's an exotic niche that doesn't exist in our solar system, and could offer new possibilities for finding life. They're particularly interested in a newly-defined type of planet that could exist within that range: Hycean worlds, which would possess water-rich interiors, planet-spanning oceans and atmospheres rich in hydrogen gas. The Madhusudhan team's detection of methane and carbon dioxide gases on K2-18 b supports his argument that the planet might have surface water, as does the fact that they did not find ammonia, which is soluble in water — if that's detected in the atmosphere, there probably isn't an ocean. But while DMS is a biosignature here on Earth, other scientists point out that it could be cooked up by some other process elsewhere, just as it can be produced in a laboratory for industrial purposes. Some scientists have suggested other possible explanations for the signals found by Madhusudhan's team, including statistical noise. Two findings within the past year bolster these criticisms. One, described last October, is the presence of dimethyl sulfide in a comet named 67P/Churyumov-Gerasimenko, which no one would argue suggests biological activity. Madhusudhan says that does nothing to disprove his hypothesis; comets are known to be little laboratories that can cook up all sorts of unlikely things. 'The same comet also has molecular oxygen in it, right?' he countered. 'It also has methane and other molecules, including amino acids." Finding something in a comet, he said, "doesn't mean that it can't be a biosignature in a planetary atmosphere, because those are two very different environments." Another finding that may cast doubt on the idea that DMS equates to the presence of life is the discovery of dimethyl sulfide, which here on Earth makes the sea smell like the sea, drifting around in deep space between the stars. Reporting on the open science platform Arxiv in February, an international group of astronomers said they found DMS during an ultra-deep molecular line survey, which uses fancy telescopes to look at a spectrum of wavelengths in one particular stretch of outer space and then catalog its chemical composition and physical properties, such as temperature and density. In this case, they pointed their telescopes toward a Galactic Center molecular cloud named G+0.693-0.027. And there they found dimethyl sulfide, just vibing in the void.
Yahoo
2 days ago
- General
- Yahoo
Astronomers thought they found signs of life on distant planet. New studies are skeptical
Back in April, the world became captivated by the news that maybe, just maybe, we weren't alone in the universe after all. If extraterrestrials were to exist on a distant exoplanet as a team of astronomers theorized, it wouldn't exactly be intelligent life, but – hey – it was something. The explosive findings came from a team of researchers at the University of Cambridge who studied data from NASA's James Webb Space Telescope to find molecules in the atmosphere of a planet known as K2-18b that could have been created by organisms akin to marine algae. But then along came other independent astronomers who took their own look at the data and came to their own highly skeptical conclusions. A series of studies since the April 17 announcement have cast doubt on the sensational claim that what the initial researchers had found was "the strongest evidence yet" that life exists anywhere else besides Earth. "The data we have so far is much too noisy for the proof that would be needed to make that claim,' Rafael Luque, an astronomer at the University of Chicago, who led the most recent study, said in a statement. 'There's just not enough certainty to say one way or the other.' Here's everything to know about K2-18b, and just what potential it has to harbor alien life. K2-18b, which orbits a red dwarf star more than 120 light-years from Earth, has for years intrigued astronomers who believe it could be among the best places to search for signs of extraterrestrial life. The cosmic body is an exoplanet, meaning it orbits a star outside of Earth's own solar system. First discovered in 2015 during NASA's planet-hunting K2 mission, K2-18b likely orbits its star in what astronomers refer to as the "habitable zone" – where conditions could allow for water. In a nod to the classic fairy tale, astronomers even refer to these regions as "Goldilocks" zones because conditions have to be just right – neither too hot nor too cold – for water to remain in liquid form and pool on planetary surfaces. Interestingly, K2-18b, which is 8.6 times bigger than Earth, isn't rocky like our planet. Rather, observations have allowed scientists to conclude that the exoplanet could be a Hycean world covered by ocean water underneath a hydrogen-rich atmosphere. Could alien life thrive on K2-18b? What to know about the distant exoplanet The latest findings on K2-18b came from a team of researchers led by Nikku Madhusudhan, an astrophysicist at the University of Cambridge in England. Because the planet is too far and too faint to observe directly with ground telescopes, astronomers had to get creative. In this case, the team studied data from the Webb Telescope gathered from observing K2-18b as the planet crossed in front of its star, causing starlight to filter through the planet's atmosphere. As the light passed through the planet's atmosphere, different amounts of light were blocked at different wavelengths, depending on what molecules are present. That's what led Madhusudhan and his team to detect hints of sulfur-based gases dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) in the atmosphere – both molecules from the same chemical family. On Earth, the gases are only produced by life, primarily microbial life such as marine algae like phytoplankton, according to the researchers. Since then, at least three different studies have largely dismissed the notion that any compelling evidence has been found to yet suggest life exists on K2-18b. In the most recent study led by Luque, researchers reviewed data from multiple observations of the planet. After combining observations of K2-18b in both the near-infrared light and longer wavelengths of mid-infrared light, the team concluded that it did not detect dimethyl sulfide. What's more, they found that other molecules, not just those possibly indicating signs of life, could explain the questionable discovery. In an earlier study published to arXiv, Jake Taylor, an astrophysicist at the University of Oxford, took a look at the Webb telescope data using a common data model for exoplanet studies and came to much the same conclusion: Taylor found no evidence of the atmospheric clues that were so integral in the Cambridge study's findings. Madhusudhan, who has issued rebuttals to some of the findings dismissing his potential discovery, has readily acknowledged that his team's observations are in need of further review. In announcing the findings, Madhusudhan conceded the molecules observed could have occurred by chance or could be the result of previously unknown chemical processes at work on K2-18b. Regardless, it appears astronomers all agree that we may not be as close as we thought to determining whether anything does indeed live on K2-18b. 'Answering whether there is life outside the solar system is the most important question of our field. It is why we are all studying these planets,' Luque said in a statement. 'We are making enormous progress in this field, and we don't want that to be overshadowed by premature declarations.' Eric Lagatta is the Space Connect reporter for the USA TODAY Network. Reach him at elagatta@ This article originally appeared on USA TODAY: Planet K2-18b life signs discovery now in doubt
Observer
5 days ago
- Science
- Observer
New studies dismiss signs of life on distant planet
In April, a team of astronomers announced that they might — just might — have found signs of life on a planet over 120 light-years from Earth. The mere possibility of extraterrestrial life was enough to attract attention worldwide. It also attracted intense scrutiny from other astronomers. Over the past month, researchers have independently analyzed the data, which suggested that the planet, called K2-18b, has a molecule in its atmosphere that could have been created by living organisms. Three different analyses have all reached the same conclusion: They see no compelling evidence for life on K2-18b. 'The claim just absolutely vanishes,' said Luis Welbanks, an astronomer at Arizona State University and an author of one of the studies. The debate has less to do with the existence of alien life than with the challenge of observing distant planets. We can see a nearby planet like Jupiter because it reflects enough sunlight to become visible to the naked eye. But a planet like K2-18b is so far away that it becomes invisible not just to the naked eye but to conventional telescopes. Astronomers have devised a series of increasingly sophisticated tricks to glean information about distant planets. They can measure the wobble of stars and the gravity of planets orbiting them. In 2010, researchers caught a glimpse of GJ 1214b, a planet 48 light-years away, as it passed in front of the star it orbits. When the star's light shone through the planet's atmosphere, certain wavelengths were absorbed, indicating that GJ 1214b might have an atmosphere rich in water vapor. In 2022, astronomers began using a powerful new tool to peer at distant planets in this way. They pointed the James Webb Space Telescope at faraway solar systems and began detecting exquisitely faint patterns in starlight, clues to the complexity of exoplanet atmospheres. The following year, Nikku Madhusudhan, an astronomer at the University of Cambridge, and his colleagues zeroed in on K2-18b as it passed in front of its star, using instruments on the Webb telescope that are extremely sensitive to near-infrared light. As K2-18b passed in front of the star, the starlight underwent a subtle shift, caused by a planetary atmosphere containing hydrogen, carbon dioxide, and methane, the researchers concluded. They also found suggestive hints of a fourth gas, dimethyl sulfide, which could be a very big deal. On Earth, the only source of dimethyl sulfide in the atmosphere is life. Photosynthetic microbes in the ocean produce the molecule as a defense against ultraviolet light from the sun. The molecule escapes their cells and ends up in the air. But the signal was so faint that it was hard to be certain that it was real. So Madhusudhan's team arranged to look again at K2-18b in 2024. This time, they used a different instrument on the space telescope, which looks at longer wavelengths of mid-infrared light. In the team's second search, they again found a signature of dimethyl sulfide, this one seemingly even stronger than the first. In April, Madhusudhan and his colleagues described their results in a paper published in the Astrophysical Journal Letters. Speaking at a news conference the day before, Madhusudhan said there was only 'a three-in-a-thousand chance of this being a fluke.' Rafael Luque, an astronomer at the University of Chicago, characterized Madhusudhan as a world expert on exoplanets. 'Madhu has been a pioneer in the field,' he said. 'I have the utmost respect for that team.' Nevertheless, Luque and his colleagues decided to take a look at the data for themselves. For their own analysis, the scientists combined all the observations of K2-18b in both the near-infrared and mid-infrared wavelengths. On May 19, they reported that this combined data contained strong signals of hydrogen, carbon dioxide and methane, but no clear evidence of dimethyl sulfide. The critics argue that the new mid-infrared observations were much weaker than those in the near-infrared. On its own, they say, the mid-infrared light could fool researchers with faint noise masquerading as a real signal of dimethyl sulfide. 'I can just say straight up there is no statistically significant signal in the data that was published a month ago,' Jacob Bean said. Bean, an astronomer at the University of Chicago who discovered GJ 1214b's atmosphere, worked with Luque on the May 19 study. Welbanks, a former student of Madhusudhan's, and his colleagues analyzed the K2-18b data differently. If the mid-infrared signal was genuine, did it have to come from dimethyl sulfide? The team considered 90 molecules that could plausibly be produced on a planet like K2-18b. Those molecules didn't have to be produced by life, however; chemical reactions driven by sunlight could be enough. The researchers concluded that the mid-infrared signal might have been produced by 59 of the 90 molecules. The strongest candidate in their analysis was not dimethyl sulfide but propyne, a gas that welders use as fuel. Welbanks and his colleagues aren't claiming that propyne is present on K2-18b. They simply argue that the faint light from the planet's atmosphere can create ambiguous patterns that might be the result of one of many gases. Such scant data certainly isn't sufficient to consider any planet to be a possible home for life. On May 15, Madhusudhan and his colleagues responded to Welbanks' team with a study of their own. They examined 650 possible molecules that might be in K2-18b's atmosphere; dimethyl sulfide ended up among the molecules at the top of the list. 'We're exactly where we left off a month ago; it's a good candidate,' Madhusudhan said. Welbanks said the new study by Madhusudhan simply provided more evidence that dimethyl sulfide does not stand out compared to other possible molecules on K2-18b. 'In effect, this is a self-rebuttal,' he said. It's possible that the debate over K2-18b could be resolved within months. Last year, Renyu Hu, an astronomer at the Jet Propulsion Laboratory, and his colleagues made more near-infrared observations of the planet. They are now preparing their results. 'It will include substantially more data than previously published,' Hu said. Bean said the new observations could dispel much of the confusion about K2-18b. 'The science is working,' he said. 'It's going to play out pretty quickly, and I think we'll have some clarity.' This article originally appeared in
Yahoo
7 days ago
- Science
- Yahoo
Doubts over hope of alien life on exoplanet K2-18b as case for biosignatures weakens
A growing number of studies have cast doubt on earlier claims about signs of life on K2-18b, a planet 124 light-years away in the Leo constellation, concluding that the available data doesn't support such bold interpretations. Last month, scientists had announced that they might have identified what appeared to be the most promising signs of alien life discerned so far on the distant planet. However, latest research contends that there was not enough evidence to estimate alien presence. K2-18b orbits within the habitable zone of its star, making it a compelling target for the search of alien life due to the potential presence of liquid water. Astronomers working with the James Webb Space Telescope drew global attention in April by reporting possible traces of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) in the planet's atmosphere. On Earth, these compounds are produced exclusively by living organisms such as marine algae, which is why they are considered potential biosignatures—chemical hints that life might exist elsewhere. Led by Cambridge University's Nikku Madhusudhan, the research team was careful to stress that the potential biosignature was far from conclusive. The signal reached a three-sigma level of statistical significance, meaning there remains a small but meaningful possibility that the result was a fluke. Two of Madhusudhan's former students, Luis Welbanks of Arizona State University and Matthew Nixon of the University of Maryland, were part of a team that re-examined the data behind the initial announcement. In a preprint study published online towards the end of last month, they reported that when using alternative statistical models, the signals originally interpreted as potential biosignatures no longer stand out. In one approach, the researchers broadened the pool of possible atmospheric chemicals from 20 to 90, significantly weakening the case for a unique biological explanation. Embracing the ongoing scientific discussion, Madhusudhan highlighted the importance of keeping an open mind throughout the research process. His team added to the conversation by releasing a new preprint study last week that expanded the list of potential atmospheric chemicals to 650. Among the top candidates identified as an indicator of alien life was dimethyl sulfide (DMS). Meanwhile, dimethyl disulfide (DMDS), which had featured prominently in their earlier announcement, was no longer considered a leading possibility. Astronomers observe distant exoplanets like K2-18b by tracking their passage across their host stars, which allows them to analyze how molecules in the planet's atmosphere absorb specific wavelengths of starlight. Earlier this week, a study led by postdoctoral researcher Rafael Luque at the University of Chicago combined Webb's observations of K2-18b in both near-infrared and mid-infrared wavelengths. The research found no statistically significant evidence for dimethyl sulfide (DMS) or dimethyl disulfide (DMDS). In addition, an earlier paper by Oxford astrophysicist Jake Taylor, using a basic statistical method, also reported no strong signs of biosignatures. However, Madhusudhan dismissed Taylor's paper noting the simple exercise used to draw conclusions was far from a robust method to observe physical phenomena. The scientist also highlighted that more data on K2-18b will be collected over the next year, which should help provide a clearer and more definitive picture.
Malay Mail
24-05-2025
- Science
- Malay Mail
Space spat: Webb hints at life — but not everyone's buying it
PARIS, May 25 — When astronomers announced last month they might have discovered the most promising hints of alien life yet on a distant planet, the rare good news raised hopes humanity could soon learn we are not alone in the universe. But several recent studies looking into the same data have found that there is not enough evidence to support such lofty claims, with one scientist accusing the astronomers of 'jumping the gun'. The debate revolves around the planet K2-18b, which is 124 light years away in the Leo constellation. The planet is thought to be the right distance from its star to have liquid water, making it a prime suspect in the search for extraterrestrial life. Last month, astronomers using the James Webb Space Telescope made headlines by announcing they had detected hints of the chemicals dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) on the planet. These chemicals are only produced by life such as marine algae on Earth, meaning they are considered potential 'biosignatures' indicating life. The astronomers, led by Cambridge University's Nikku Madhusudhan, expressed caution about the 'hints' of a biosignature, emphasising they were not claiming a definitive discovery. Their detection had reached a three-sigma level of statistical significance 'which means there is still a three in 1,000 chance of this being a fluke,' Madhusudhan said at the time. Biosignatures 'vanish' Two of Madhusudhan's former students, Luis Welbanks of Arizona State University and Matthew Nixon of Maryland University, were among the researchers who have since re-analysed the data behind the announcement. When deploying other statistical models, 'claims of a potential biosignature detection vanish', according to their preprint study published online late last month. Like the other papers since the April announcement, it has not been peer-reviewed. In one model, Welbanks and colleagues expanded the number of possible chemicals that could explain the signals detected by Webb to 90 from the original 20. More than 50 received a 'hit', Welbanks told AFP. 'When you detect everything, did you really detect anything?' he asked. They are not saying the planet definitely does not have DMS — just that more observations are needed, Welbanks added. 'Arguments are healthy' Madhusudhan welcomed the robust debate, saying that remaining open to all possibilities is an essential part of the scientific method. 'These sorts of arguments are healthy,' he told AFP. His team even went further, releasing their own preprint study last week that expanded the number of chemicals even further to 650. The three most 'promising' chemicals they found included DMS but not DMDS — a major part of the team's announcement in April. The other two chemicals were diethyl sulfide and methyl acrylonitrile, the latter of which is toxic. Madhusudhan admitted that these little-known chemicals are likely not 'realistic molecules' for a planet like K2-18b. Welbanks pointed out that 'in the span of a month — with no new data, with no new models, with no new laboratory data — their entire analysis changed'. 'Closest we have ever been' Telescopes observe such far-off exoplanets when they cross in front of their star, allowing astronomers to analyse how molecules block different wavelengths of light streaming through their atmosphere. Earlier this week, a paper led by Rafael Luque at the University of Chicago combined Webb's observations of K2-18b in both the near-infrared and mid-infrared wavelengths of light. It also found 'no statistical significance for DMS or DMDS', the paper said. An earlier paper by Oxford astrophysicist Jake Taylor using a basic statistical test also found no strong evidence for any biosignatures. Madhusudhan dismissed the latter paper, saying the simple exercise did not account for observing physical phenomena. He also stood by his research, saying he was 'just as confident' in the work as he was a month ago. More data about K2-18b will come in over the next year which should offer a much clearer picture, Madhusudhan added. Even if the planet does have DMS, it is not a guarantee of life — the chemical has been detected on a lifeless asteroid. However, many researchers do believe that space telescopes could one day collect enough evidence to identify alien life from afar. 'We are the closest we have ever been' to such a moment, Welbanks said. 'But we have to use the frameworks that are in place and build up (evidence) in a reliable method, rather than using non-standard practices and jumping the gun — as has been done in this particular case,' Nixon added. — AFP
