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Scientific American
2 days ago
- Science
- Scientific American
How a Passing Star Could Oust Planets from the Solar System
There's a bit of a paradox about our galaxy: it's both jam-packed with stars and cavernously empty. The Milky Way is crowded in the sense that it holds hundreds of billions of stars, as well as sprawling clouds of gas and dust. But even so, there is a lot of elbow room: the nearest star to the sun is more than four light-years distant, separated from us by tens of trillions of kilometers. That's an immense distance and difficult to even analogize. Saying our fastest space probes would take tens of thousands of years to reach the nearest star is still such a ponderous concept that it's hard to grasp. Of course, there are more crowded spots, too. Some stellar clusters pack thousands of stars into a small volume of space, and the bustling galactic center swarms with stars. But out here in the galactic suburbs, stars are more spread out, providing one another plenty of room as they orbit through the Milky Way. On supporting science journalism If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today. Still, given enough time, some stars will encroach on our personal space. About 80,000 years ago a small red dwarf called Scholz's star passed the sun at a distance of just 0.85 light-year. Looking ahead, about 1.3 million years hence, the star Gliese 710 will give us a close shave by 0.17 light-year. That may seem like a long time on a human scale, but that's barely a tick of the galactic clock. The sun and its retinue of planets, asteroids and comets have been around for more than 4.5 billion years. Across that yawning stretch of time, it's a near certainty the sun has had some close encounters of the stellar kind. What sort of effect does that have on the solar system? We know that the sun is surrounded by a vast halo of trillions of icy bodies collectively called the Oort Cloud; although each individual object is far too faint to see with modern equipment, every now and again, one will drop down into the inner solar system and grace our skies as a long-period comet. Estimates of the cloud's size vary, but it could stretch more than a light-year from the sun. A star passing through that region could gravitationally poke at those ice balls, nudging hundreds or even thousands of them toward the sun, and some of them could hit an inner planet. Some researchers have even speculated that such a close pass could provoke a mass extinction event. Research published in the Astrophysical Journal Letters showed that the passage of Scholz's star was unlikely to trigger such an event; the star is too much of a lightweight and was moving too quickly to significantly jostle the Oort Cloud and rain death upon our world. Given enough time, however, other stars could indeed stir up trouble in the distant reaches of the outer solar system. Happily, we probably have thousands of millennia to prepare. But such a celestial drive-by can have other unsettling consequences as well. Many astronomers have wondered about the long-term stability of the solar system's planets, given that they interact with each other gravitationally over the eons. The early solar system was wracked with profound instabilities, but more recently such effects have been far more subtle. Oddly enough, Mercury, the innermost planet, is particularly susceptible to these. The physics behind this is complex, but in a nutshell, small changes in the orbit of Neptune—the major planet most affected by a star passing by—propagate inward. It tugs on Uranus, which tugs on Saturn, which tugs on Jupiter, and the solar system's most massive planet affects everything else. Its orbit and that of Mercury can fall into a resonance in which the orbital periods (the 'years' of both planets) are simple ratios of each other. When this happens, Mercury gets an added kick (literally, like when a child on a playground swing kicks at the right moment, pumping up their oscillations). It's been known for decades that these effects can change the ellipticity of Mercury's orbit, sometimes stretching it out into a long oval. If the orbit were to get too elongated, Mercury could fall into the sun or get close enough to Venus to get flung out of the solar system. Mars, too, could fall prey to this; like Mercury, it has a more oval-shaped orbit than that of Earth or Venus and can find its orbit changing shape radically over a sufficiently long time frame. In the past, most of those simulations assumed the solar system to be in isolation, with no other stars nearby sticking their noses in our business. But we know that's not the case, and such stellar interference must be accounted for to understand the solar system's evolution. Many simulations that do include passing stars don't usually take all the effects into complete consideration; for example, they run their models for a few tens of millions of years even though it can take billions for gradually growing instabilities to have an impact. Others have used limited modeling of stellar encounters, meaning that they haven't included the entire possible range of masses, velocities and passage distances expected from stars in the galaxy. Research published online in the planetary science journal Icarus last month attempts to address all these factors in more robust simulations of the solar system's dynamic evolution. What the authors find is that some celestial bodies are a little less stable than previously thought, given how often stars pass by the sun. Not surprisingly, Pluto is the hardest hit. (The researchers only modeled the eight major planets plus Pluto.) Previously, Pluto was thought to have a pretty stable orbit, but the new simulations show that over the course of about five billion years, there's a 4 percent chance for Pluto to be ejected from the solar system entirely. These passes also increase Mercury's odds of an unhappy end. Previous studies showed a roughly 1 percent chance of it dropping into the sun or being ejected from the solar system because of planetary dynamics in the next five billion years or so, but according to the new study, there's an additional 0.56 percent chance that these events could occur via stellar interactions. Mars, too, has a 0.3 percent chance of the fate of getting an extreme sunburn or starlessly wandering the galaxy. Earth isn't immune, either. The new research finds that our own fair world has a 0.2 percent chance of being involved in a planetary collision or ejected into interstellar space. The odds are low, certainly, but higher than I'd care for given the world-shattering stakes. At this point I think I should remind you of the timescale involved: we're talking five billion years into the future, which is roughly the same amount of time that's elapsed since the solar system was born in the first place. That's a long time, so this is not something you or I should personally worry about. Plus, we don't know of any stars that will pass terribly close to us for several million years anyway. In the shorter term, I'm more concerned about—in chronologically ascending order— global warming (at the timescale of decades), medium-sized asteroids (centuries), supervolcanoes (hundreds of millennia) and giant-sized asteroids (tens of millions of years). Remember, too, that the solar system has been around a long time and, crucially, Earth is still here. It's been batted around a bit, but life persists. Over the very long term, the universe is a dangerous place, but for now, for us—cosmically speaking, at least—we can breathe easy.
Yahoo
2 days ago
- Science
- Yahoo
A Gigantic Megacomet Is Erupting as It Zooms through the Solar System
There's a giant ball of ice barreling through the solar system right now, and it's bigger than any we've seen before. It poses no threat to Earth, but this comet, called C/2014 UN271 (Bernardinelli-Bernstein), has enraptured astronomers ever since its discovery in 2021. The hulking object, sometimes jovially called a 'megacomet,' is 100 times bigger than most comets we see in the solar system. And now we're learning more about it than ever before as it zooms toward its closest approach to our sun in 2031. In a study published in the Astrophysical Journal Letters on June 12, Nathan Roth of American University and his colleagues report the first conclusive detection of carbon monoxide on the megacomet. That's a crucial finding because it might tell us more about the object's origins, history and likely upcoming behavior as it dives deeper into the solar system. 'We wanted to test what drives activity in this comet,' Roth says. 'It's so far from the sun and so cold that trying to explain what makes a comet 'work' at these distances is difficult.' C/2014 UN271 was first imaged by chance in observations from 2014. Seven years later, when astronomers actually spotted it in their archives, the comet was at more than 20 times the Earth-sun distance, inside the orbit of Neptune. But they also found that it is on a path that will bring it nearly to Saturn's orbit in 2031 before it heads out again. The comet's orbit is huge, extending out to about 55,000 times the Earth-sun distance—87 percent of a light-year and well out into the Oort Cloud of icy objects that surrounds our sun. [Sign up for Today in Science, a free daily newsletter] Following the comet's discovery astronomers used various telescopes, including the James Webb Space Telescope and the Hubble Space Telescope, to scrutinize it from afar. The object was initially thought to be as big as 370 kilometers (230 miles) across. Revised observations showed it to be about 140 kilometers (87 miles) wide. But that's still the biggest anyone has ever seen—most comets in the solar system are only one or two kilometers across. 'It's huge,' says Quanzhi Ye, an astronomer at the University of Maryland, who was not involved in Roth's study. 'It represents a part of the cometary spectrum that we don't understand.' Some of those observations revealed bursts of activity from the comet, which sprouted an enormous, enveloping 'coma' of expelled gas that stretches some 250,000 kilometers (155,000 miles) across (more than half the distance from the Earth to the moon). To find out the cause of this activity, Roth and his team used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to observe the comet in radio waves for about eight hours in March 2024. They found a clear trace of carbon monoxide spewing from the comet, suggesting that its sprawling coma is fueled, at least in part, by carbon monoxide ice sublimating—turning from solid to gas—as the comet approaches the sun. The carbon monoxide appears to be vented in jets from spots on the object's surface, possibly the result of the overhead sun heating a localized region and causing the ice to sublimate. 'If you were standing on the comet, and the sun was right overhead, this is the area where the sun is heating the surface the most and the jet originates from,' Roth says. What's not clear so far, however, is how fast the comet is spinning and whether the location of the jets is changing over time. 'Are there different jets being activated at different times? We don't know yet,' Roth says. As C/2014 UN271 gets closer, other ices that are often found on comets, such as methane and hydrogen sulfide ice, might start to sublimate, too, and add their own contributions to the object's activity. 'As we continue to monitor it, we'll be able to get a better idea of the chemical fingerprint that's preserved inside the comet,' Roth says. Rosita Kokotanekova, an astronomer at the Rozhen National Astronomical Observatory in Bulgaria, who was not part of Roth's research team, says the detection of carbon monoxide is useful because it is 'important to identify what prompts activity at these large distances.' Researchers have witnessed gas venting from other, much smaller comets at a similar distance, 'which was very puzzling,' she adds. 'People were trying to figure out what exactly is causing this activity [so far from the sun].' C/2014 UN271's size makes it an especially alluring target for study. The presence of carbon monoxide ice is doubly interesting: Analysis of available data about the comet revealed that it first exhibited signs of activity at more than 25 times the Earth-sun distance. But according to theoretical models, its carbon monoxide ice should have been sublimated by the sun's rays when the object was even farther out in the solar system. This discrepancy may mean the comet made a pass of the sun before, with sublimation first eating away at layers of ice on its surface and its current activity only being kickstarted at closer distances, when heat from sunlight reached ice deeper within the object. Finding a behemoth like C/2014 UN271, Kokotanekova says, could hint at the existence of a whole class of gigantic progenitor comets. Such comets might have been the first large, icy objects to coalesce in the solar system, after which they could have eventually broken apart to form smaller comets. 'It's possible that the small objects are mostly fragments, while the large ones, like UN271, have never collided with anything,' she says. That might mean there are more primordial megacomets awaiting discovery. If so, the recently completed Vera C. Rubin Observatory in Chile, which will begin a 10-year panoramic survey of the heavens later this year, could find more of them. 'It's so sensitive that it will certainly pick up comets of this size, quite probably even further away from us,' Ye says. Rubin's wide eye on the sky should also give us more information on C/2014 UN271 itself, says Meg Schwamb, an astronomer at Queen's University Belfast uninvolved with this latest finding. 'Rubin's going to watch it come in,' she says. That could help us get a better handle on its activity, in partnership with telescopes like ALMA. 'You need both of those pieces of information—if it got brighter, and whether the amount of carbon monoxide changed—to tell you what's going on,' Schwamb says. For now Comet UN271 remains a fascinating target of study, a giant comet like no other that is giving us a unique window into the dark frontiers of the outer solar system. 'This is just an incredibly exciting object,' Roth says. And, for astronomers eager to learn more about this and other mega comets, the best is yet to come.
Scientific American
3 days ago
- Science
- Scientific American
Astronomers Spy Jets Spewing from Megacomet Zooming through the Solar System
There's a giant ball of ice barreling through the solar system right now, and it's bigger than any we've seen before. It poses no threat to Earth, but this comet, called C/2014 UN271 (Bernardinelli-Bernstein), has enraptured astronomers ever since its discovery in 2021. The hulking object, sometimes jovially called a 'megacomet,' is 100 times bigger than most comets we see in the solar system. And now we're learning more about it than ever before as it zooms toward its closest approach to our sun in 2031. In a study published in the Astrophysical Journal Letters on June 12, Nathan Roth of American University and his colleagues report the first conclusive detection of carbon monoxide on the megacomet. That's a crucial finding because it might tell us more about the object's origins, history and likely upcoming behavior as it dives deeper into the solar system. 'We wanted to test what drives activity in this comet,' Roth says. 'It's so far from the sun and so cold that trying to explain what makes a comet 'work' at these distances is difficult.' C/2014 UN271 was first imaged by chance in observations from 2014. Seven years later, when astronomers actually spotted it in their archives, the comet was at more than 20 times the Earth-sun distance, inside the orbit of Neptune. But they also found that it is on a path that will bring it nearly to Saturn's orbit in 2031 before it heads out again. The comet's orbit is huge, extending out to about 55,000 times the Earth-sun distance—87 percent of a light-year and well out into the Oort Cloud of icy objects that surrounds our sun. On supporting science journalism If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today. Following the comet's discovery astronomers used various telescopes, including the James Webb Space Telescope and the Hubble Space Telescope, to scrutinize it from afar. The object was initially thought to be as big as 370 kilometers (230 miles) across. Revised observations showed it to be about 140 kilometers (87 miles) wide. But that's still the biggest anyone has ever seen—most comets in the solar system are only one or two kilometers across. 'It's huge,' says Quanzhi Ye, an astronomer at the University of Maryland, who was not involved in Roth's study. 'It represents a part of the cometary spectrum that we don't understand.' Some of those observations revealed bursts of activity from the comet, which sprouted an enormous, enveloping 'coma' of expelled gas that stretches some 250,000 kilometers (155,000 miles) across (more than half the distance from the Earth to the moon). To find out the cause of this activity, Roth and his team used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to observe the comet in radio waves for about eight hours in March 2024. They found a clear trace of carbon monoxide spewing from the comet, suggesting that its sprawling coma is fueled, at least in part, by carbon monoxide ice sublimating—turning from solid to gas—as the comet approaches the sun. The carbon monoxide appears to be vented in jets from spots on the object's surface, possibly the result of the overhead sun heating a localized region and causing the ice to sublimate. 'If you were standing on the comet, and the sun was right overhead, this is the area where the sun is heating the surface the most and the jet originates from,' Roth says. What's not clear so far, however, is how fast the comet is spinning and whether the location of the jets is changing over time. 'Are there different jets being activated at different times? We don't know yet,' Roth says. As C/2014 UN271 gets closer, other ices that are often found on comets, such as methane and hydrogen sulfide ice, might start to sublimate, too, and add their own contributions to the object's activity. 'As we continue to monitor it, we'll be able to get a better idea of the chemical fingerprint that's preserved inside the comet,' Roth says. Rosita Kokotanekova, an astronomer at the Rozhen National Astronomical Observatory in Bulgaria, who was not part of Roth's research team, says the detection of carbon monoxide is useful because it is 'important to identify what prompts activity at these large distances.' Researchers have witnessed gas venting from other, much smaller comets at a similar distance, 'which was very puzzling,' she adds. 'People were trying to figure out what exactly is causing this activity [so far from the sun].' C/2014 UN271's size makes it an especially alluring target for study. The presence of carbon monoxide ice is doubly interesting: Analysis of available data about the comet revealed that it exhibited signs of activity when it was more than 25 times as far out as the Earth-sun distance. But according to theoretical models, its carbon monoxide ice should have been sublimated by the sun's rays when the object was even farther out in the solar system. This discrepancy may mean the comet made a pass of the sun before, with sublimation first eating away at layers of ice on its surface and its current activity only being kickstarted at closer distances, when heat from sunlight reached ice deeper within the object. Finding a behemoth like C/2014 UN271, Kokotanekova says, could hint at the existence of a whole class of gigantic progenitor comets. Such comets might have been the first large, icy objects to coalesce in the solar system, after which they may could have eventually broken apart to form smaller comets. 'It's possible that the small objects are mostly fragments, while the large ones, like UN271, have never collided with anything,' she says. That might mean there are more primordial megacomets awaiting discovery. If so, the recently completed Vera C. Rubin Observatory in Chile, which will begin a 10-year panoramic survey of the heavens later this year, could find more of them. 'It's so sensitive that it will certainly pick up comets of this size, quite probably even further away from us,' Ye says. Rubin's wide eye on the sky should also give us more information on C/2014 UN271 itself, says Meg Schwamb, an astronomer at Queen's University Belfast uninvolved with this latest finding. 'Rubin's going to watch it come in,' she says. That could help us get a better handle on its activity, in partnership with telescopes like ALMA. 'You need both of those pieces of information—if it got brighter, and whether the amount of carbon monoxide changed—to tell you what's going on,' Schwamb says. For now Comet UN271 remains a fascinating target of study, a giant comet like no other that is giving us a unique window into the dark frontiers of the outer solar system. 'This is just an incredibly exciting object,' Roth says. And, for astronomers eager to learn more about this and other mega comets, the best is yet to come.
Japan Times
28-04-2025
- Science
- Japan Times
In a galaxy far, far away ... did we find life?
In the last few years, astronomers have discovered that our galaxy is teeming with planets unlike anything in our solar system. One such exotic world, K2-18b, made the news recently over what some scientists claim is tentative evidence of what could be signs of life. Others say it's far too soon to tell. K2-18b weighs in at more than eight times the mass of Earth, orbits a red dwarf star every 33 days and just might be covered with a massive ocean and blanketed by an atmosphere complete with water vapor and rain clouds, according to work done by two teams of researchers. Researchers now say they've detected hints of two compounds that would make K2-18b smell like the sea. Dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) are produced on Earth by phytoplankton and other marine microorganisms. The evidence isn't strong enough to declare alien life — yet — but with more observations, it might be. Scientists do agree on the astonishing fact that it's possible to use tiny changes in light reaching us to measure what's in the atmospheres of planets orbiting stars trillions of miles away. Previous observations of K2-18b with the Hubble Space Telescope detected carbon dioxide, methane and water vapor in its atmosphere. The newer findings, published in the Astrophysical Journal Letters, were done using the James Webb Space Telescope and strengthened the case for the sea-scented sulfur compounds. With a mass and size in between that of Earth and Neptune, it's called a sub-Neptune and fits into a size range that's not found in our solar system. The red dwarf it orbits is much dimmer than our sun but is closer, so it's warm enough for water to remain liquid. Models show it might be covered in an ocean 600 miles deep, more than 100 times the depth of our oceans. However, scientists say they can't rule out that K2-18b is a molten hellscape or a gaseous planet with no surface. The possible detection of DMS and DMDS is exciting because they constitute a biosignature — a chemical unlikely to have formed without life. Abundant oxygen here on Earth would be a similar giveaway to life-seeking alien astronomers since we acquired our oxygen-rich atmosphere only after the evolution of photosynthesis. Back in 1999, Sarah Seager, an astrophysicist at MIT, proposed a way to search for life by looking for such biosignature compounds in the atmospheres of planets around other stars — even though most such planets are invisible even to the most powerful telescopes and have to be detected indirectly by changes in stellar brightness or motion. Seager's idea would only work in cases where a planet's orbit takes it between us and its parent star, causing a slight periodic dip in starlight, like a mini eclipse. In such cases, the planet's atmosphere would alter the starlight that passes through, like a flashlight passing through fog, Seager told me. She proposed back then that scientists could observe changes in the spectrum of starlight to infer which atmospheric gases were present. Since then, Seager said, astronomers have been surprised to find hundreds of these mid-sized sub-Neptunes. "We have no solar system counterparts,' she said, "yet it appears to be the most common planet in our galaxy.' And while studying distant planets isn't the primary purpose of the James Webb telescope, it's given astronomers a new window into their compositions and potential habitability. "It's just absolutely gratifying to see the telescope being used to study untold numbers of exoplanet atmospheres ... atmospheres of all kinds that we never anticipated existing,' she said. One of her graduate students, now at Cambridge University, led this new work on K2-18b. She said they still need stronger evidence that they really detected the dimethyl sulfide and dimethyl disulfide, and then they need to show that these gases couldn't be produced by some nonbiological process. Meanwhile, other lines of evidence suggest life is abundant in the universe. Microfossils show that Earth was inhabited soon after it cooled enough to form a solid crust and the building blocks of life have been detected far from Earth. A recent NASA mission to sample an asteroid named Bennu showed it held amino acids, which make up proteins and nucleotides — the same building blocks humans use to make RNA and DNA. Detecting ET probably won't come as a single discovery credited to one group, said astrophysicist Adam Frank of the University of Rochester. Frank compares life detection to the understanding that the universe is expanding. That wasn't a scientific consensus until it was confirmed with multiple independent lines of evidence over the course of the 20th century. He said it's possible to detect not only biosignatures on distant worlds but also "techno-signatures,' including gases unlikely to be produced except through alien technology. That might include chlorofluorocarbons, which started to build up in our atmosphere after we created them to use as refrigerants, propellants for aerosol sprays and other applications. It may take a space telescope more powerful than the James Webb to determine which planets host life. That's why NASA is planning to launch a dedicated instrument called the Habitable Worlds Observatory. Given NASA's budget cuts, the future of this project is unknown, but it would be a shame to give up the search now when we're so close and the universe has produced so many weird and wonderful planets. F.D. Flam is a Bloomberg Opinion columnist covering science. She is host of the "Follow the Science' podcast.
Economic Times
28-04-2025
- Science
- Economic Times
New hope of extraterrestrial life? Scientists cautious about celebrating early, want recheck
Are we alone in this universe? A study led by the University of Cambridge provides a flicker of hope that it may not be so, and the answer may lie 120 light-years from Earth. The study, published in the Astrophysical Journal Letters last week, found hints of life in the distant planet named K2-18b. But astrophysicists are sceptical and say the study's results and the methodology need to be cross-checked by other researchers. According to the research, fingerprints of dimethyl sulphide and dimethyl disulphide molecules have been detected on the exoplanet's atmosphere. On Earth, these molecules are known to be produced by marine organisms. Interestingly, the most common hypothesis is that life on Earth originated in the ocean. The study provides evidence of 'three-sigma' significance -- a 99.7 per cent confidence that the results are not fortuitous -- about the strongest-yet of signs of life outside the Solar System, asserts the research team led by Nikku Madhusudhan, a professor of astrophysics and exoplanetary science. In an interview with PTI Videos last week, he said that given scope of the study's implications, his team was looking to increase the robustness of the results in future researches. Jayesh Goyal, a reader at the School of Earth and Planetary Sciences at the National Institute of Science Education and Research (NISER), Bhubaneswar, feels that the findings of the study are a big step forward and "pushes the limits of our understanding of exoplanet atmospheres and their habitability". "The observations on K2-18b's atmosphere highlight the extent to which this class of sub-Neptune or super-earth exoplanets could be characterised as these targets are extremely challenging to study," he told PTI. The exoplanet is 8.6 times massive than Earth, but smaller and less massive than Neptune. Hence it has been classified as a 'sub-Neptune' exoplanet. Scientists who study exoplanets contest the interpretation of the observations, saying the results are not statistically sound, given the immensity of claims of detecting biological activity outside the Solar System. "It is not a 'detection' according to the usual standards of exoplanet science," Ryan MacDonald, NASA Sagan Fellow at the University of Michigan in the US, told PTI. Data recorded by the James Webb Space Telescope's MIRI instrument was analysed for the study. The infrared facility looked at starlight transmitted through the exoplanet's atmosphere. "The study assumes that half of the new data from the Webb telescope can only be explained by dimethyl sulphide and dimethyl disulphide, neglecting other possible gases, thereby attaching a much higher statistical significance to the claims than the data supports," the astronomer said. Asa Stahl, an astrophysicist whose PhD at the US' Rice University focused on exoplanets, said the study made use of a "hugely powerful tool" for peering into a faraway planet's atmosphere. "It's an immensely difficult task -- trying to piece together what a planet over a hundred light years away is like from how starlight filters through its atmosphere." However, it is also a relatively new method, and astronomers are still figuring out the best practices for this sort of thing, added Stahl, engaged in science communication projects. Madhusudhan, while asserting that the team of researchers would look into fortifying the robustness of the study's results, also said, "When you have big breakthroughs and big paradigm shifts, you want to be really sure because it changes the very fabric of science and society in fundamental ways." "So then, the measure of robustness there is that we want to be sure to a level that there is less than one part in a million chance of a fluke, which is a very, very, very small chance of a statistical fluke or a 'just by chance'. We want to be that robust," he added. However, the currently claimed 'three-sigma' significance -- or a 0.3 per cent of being wrong -- would need to be tested, astrophysicists said. "Using the statistics in the study, the actual probability of the molecules not being present (in K2-18b's atmosphere) is about 28 per cent. Therefore, the announcement projects (a) near-absolute confidence in a result that has a good chance of not being real," MacDonald said. And same is the case with Stahl. "We won't know for sure how robust the finding is until other researchers test it." Astrophysicist Stephen Schmidt, a graduate research fellow at the Johns Hopkins University, US, re-analysed results from a 2023 study, in which Madhusudhan's team, using the James Webb space telescope, found abundant levels of carbon-containing gases -- methane and carbon dioxide -- and potential signs of dimethyl sulphide. Despite replicating the models used in the 2023 study, the results of the re-analysis (currently in a pre-print paper stage) differed from the original. Schmidt's team could not put limits on detectable amounts of carbon dioxide in K2-18b's atmosphere. The result indicated "a lot more methane compared to carbon dioxide" and therefore, "very difficult and unlikely for the exoplanet to have a habitable liquid water surface ocean, and also a biosphere or life", he explained. Schmidt said that while the University of Cambdrige-led study pushes the limits and tests the capabilities of the Webb telescope, which he stresses is important, "this can result in potentially exciting findings that aren't substantiated after further observations." Further, there are questions that need answers, to know for sure what is happening. One of these involves understanding the processes through which dimethyl sulphide and dimethyl sulphide molecules -- considered as predictors of life on exoplanets -- can form. Even as Madhusudhan's team is looking to address this aspect in future research, answers to the origins of the molecules could prove to be especially important as studies have found dimethyl sulphide on a comet and in the space between stars -- both 'lifeless' environments. Goyal said more observations of K2-18b using the Webb telescope, along with a detailed study of laboratory spectra of dimethyl sulphide and dimethyl disulphide, could help tighten or dispute the study's results. Further, a model's ability to detect chemicals accurately should be quoted in a paper, after "considering a wide variety of different molecules, rather than just those one assumes are there," MacDonald said. The astrophysicists said not one chemical or molecule, but a combination of chemicals or gases, produced in significant amounts, along with a deep understanding of the exoplanet's environment, would be needed before being confident of habitability. However, the methods used in the Cambridge-led study could hold promise in these pursuits. Stahl said, "If we ever discover life in another world, this method could be how we find out."
