Evidence of life on an alien planet

  ‘Strongest Evidence’ so far for life beyond our solar system found by Scientists 

In a potential landmark discovery, scientists using the James Webb Space Telescope have obtained what they call the strongest signs yet of possible life beyond our solar system, detecting in an alien planet's atmosphere the chemical fingerprints of gases which on Earth are produced only by biological processes. Astrophysics team say observation of chemical compounds may be ‘tipping point’ in search for extra-terrestrial life. A giant planet 124 light years from Earth has yielded the strongest evidence yet that extra-terrestrial life may be thriving beyond our solar system, astronomers claim. Observations by the James Webb space telescope of a planet called K2-18 b appear to reveal the chemical fingerprints of two compounds that, on Earth, are only known to be produced by life. Following are yhe some of the important points:-

Planet, called K2-18 b, is 8.6 times the mass of Earth.

Scientists do not announce discovery of actual alien life.

K2-18 b is located about 124 light-years from Earth.

Gases found are the same as those produced by algae on Earth.

The two gases, dimethyl sulfide, or DMS, and dimethyl disulfide, or DMDS, involved in Webb's observations of the planet named K2-18 b are generated on Earth by living organisms, primarily microbial life such as marine phytoplankton, algae. Detection of the chemicals, dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) would not amount to proof of alien biological activity, but could bring the answer to the question of whether we are alone in the universe much closer. “This is the strongest evidence to date for a biological activity beyond the solar system,” said Prof Nikku Madhusudhan, an astrophysicist at the University of Cambridge who led the observations. “We are very cautious. We have to question ourselves both on whether the signal is real and what it means.” He added: “Decades from now, we may look back at this point in time and recognise it was when the living universe came within reach. This could be the tipping point, where suddenly the fundamental question of whether we’re alone in the universe is one we’re capable of answering.”

This suggests the planet may be teeming with microbial life, the researchers said. They stressed, however, that they are not announcing the discovery of actual living organisms but rather a possible bio signature, an indicator of a biological process, and the findings should be viewed cautiously, with more observations needed. Nonetheless, they voiced excitement. These are the first hints of an alien world which is possibly inhabited, said astrophysicist Nikku Madhusudhan of the University of Cambridge's Institute of Astronomy, lead author of the study. Others are more sceptical, with questions remaining about whether the overall conditions on K2-18 b, are favourable to life and whether DMS and DMDS, which are largely produced by marine phytoplankton on Earth, can be reliably regarded as bio signatures. K2-18 b, which is found in the Leo constellation, is nearly nine times as massive as the Earth and 2.6 times as large and orbits in the habitable zone of its star, a cool red dwarf less than half the size of the sun. When the Hubble space telescope appeared to spot water vapour in its atmosphere in 2019, scientists declared it “the most habitable known world” beyond the solar system. The supposed water signal was shown to be methane in follow-up observations by Madhusudhan’s team in 2023. But, they argued, K2-18 b’s profile was consistent with a habitable world, covered in a vast, deep ocean, a view which remains contentious. More provocatively, the Cambridge team reported a tentative hint of DMS.

"This is a transformational moment in the search for life beyond the solar system, where we have demonstrated that it is possible to detect biosignatures in potentially habitable planets with current facilities. We have entered the era of observational astrobiology," Madhusudhan said. Madhusudhan noted that there are various efforts underway searching for signs of life in our solar system, including various claims of environments which might be conducive to life in places like Mars, Venus and various icy moons. Planets beyond our solar system are too distant to photograph or reach with robotic spacecraft. But scientists can estimate their size, density and temperature and probe their chemical makeup by tracking the exoplanet as it passes across the face of its host star and measuring starlight that has been filtered through its atmosphere. In the latest observations, wavelengths that are absorbed by DMS and DMDS, were seen to suddenly drop off as K2-18 b wandered in front of the red dwarf. “The signal came through strong and clear,” said Madhusudhan. “If we can detect these molecules on habitable planets, this is the first time we’ve been able to do that as a species … it’s mind-boggling that this is possible.”

K2-18 b orbits in the "habitable zone", a distance where liquid water, a key ingredient for life, can exist on a planetary surface. around a red dwarf star smaller and less luminous than our sun, located about 124 light-years from Earth in the constellation Leo. A light-year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km). One other planet also has been identified orbiting this star. The findings, suggest concentrations of DMS, DMDS or both (their signatures overlap) thousands of times stronger than the levels on Earth. The results are reported with a “three-sigma” level of statistical significance (a 0.3% probability that they occurred by chance) although this falls short of the gold standard for discoveries in physics. “There may be processes that we don’t know about that are producing these molecules,” Madhusudhan said. “But I don’t think there is any known process that can explain this without biology.” About 5,800 planets beyond our solar system, called exoplanets, have been discovered since the 1990s. Scientists have hypothesized the existence of exoplanets called hycean worlds, covered by a liquid water ocean habitable by microorganisms and with a hydrogen-rich atmosphere. Earlier observations by Webb, which was launched in 2021 and became operational in 2022, had identified methane and carbon dioxide in K2-18 b's atmosphere, the first time that carbon-based molecules were discovered in the atmosphere of an exoplanet in a star's habitable zone.

A challenge in identifying potential other processes is that the conditions on K2-18 b remain disputed. While the Cambridge team favour an ocean scenario, others say the data is suggestive of a gas planet or one with oceans made of magma, not water. There is a question of whether DMS could have been brought to the planet by comets, this would require an intensity of bombardment that seems improbable, or produced in hydrothermal vents, volcanoes or lightning storms through exotic chemical processes. “Life is one of the options, but it’s one among many,” said Dr Nora Hänni, a chemist at the Physics Institute of the University of Berne, whose research revealed that DMS was present on an icy, lifeless comet. “We would have to strictly rule out all the other options before claiming life.” Madhusudhan said that with hycean worlds, if they exist, "we are talking about microbial life, possibly like what we see in the Earth's oceans." Their oceans are hypothesized to be warmer than Earth's. Asked about possible multicellular organisms or even intelligent life, Madhusudhan said, "The only scenario that currently explains all the data obtained so far from JWST (James Webb Space Telescope), including the past and present observations, is one where K2-18 b is a hycean world teeming with life," Madhusudhan said. "However, we need to be open and continue exploring other scenarios."

Others say that measuring planetary atmospheres may never yield a smoking gun for life. “It’s under-appreciated in the field, but techno signatures, such as an intercepted message from an advanced civilisation, could be better smoking guns, despite the unlikelihood of finding such a signal,” said Dr Caroline Morley, an astrophysicist at the University of Texas, Austin, adding that the findings were, nonetheless, an important advance. Dr Jo Barstow, a planetary scientist at the Open University, also viewed the detection as significant, but said: “My scepticism dial for any claim relating to evidence of life is permanently turned up to 11, not because I don’t think that other life is out there, but because I feel that for such a profound and significant discovery the burden of proof must be very, very high. I don’t think this latest work crosses that threshold.” DMS and DMDS, both from the same chemical family, have been predicted as important exoplanet bio signatures. Webb found that one or the other, or possibly both, were present in the planet's atmosphere at a 99.7% confidence level, meaning there is still a 0.3% chance of the observation being a statistical fluke. The gases were detected at atmospheric concentrations of more than 10 parts per million by volume. "For reference, this is thousands of times higher than their concentrations in the Earth's atmosphere, and cannot be explained without biological activity based on existing knowledge," Madhusudhan said. At 120 light years away, there is no prospect of resolving the debate through close-up observations, but Madhusudhan notes that this has not been a barrier to the discovery of black holes or other cosmic phenomena.

"The rich data from K2-18 b make it a tantalizing world," said Christopher Glein, principal scientist at the Space Science Division of the Southwest Research Institute in Texas. "These latest data are a valuable contribution to our understanding. Yet, we must be very careful to test the data as thoroughly as possible. I look forward to seeing additional, independent work on the data analysis starting as soon as next week." K2-18 b is part of the "sub-Neptune" class of planets, with a diameter greater than Earth's but less than that of Neptune, our solar system's smallest gas planet. To ascertain the chemical composition of an exoplanet's atmosphere, astronomers analyse the light from its host star as the planet passes in front of it from the perspective of Earth, called the transit method. As the planet transits, Webb can detect a decrease in stellar brightness, and a small fraction of starlight passes through the planetary atmosphere before being detected by the telescope. This lets scientists determine the constituent gases of the planet's atmosphere. “In astronomy, the question is never about going there,” Madhusudhan said. “We’re trying to establish if the laws of biology are universal in nature. I don’t see it as: ‘We have to go and swim in the water to catch the fish.”

Webb's previous observations of this planet provided a tentative hint of DMS. Its new observations used a different instrument and a different wavelength range of light. The "Holy Grail" of exoplanet science, Madhusudhan said, is to find evidence of life on an Earth-like planet beyond our solar system. Madhusudhan said that our species for thousands of years has wondered "are we alone" in the universe, and now might be within just a few years of detecting possible alien life on a hycean world. But Madhusudhan still urged caution. "First we need to repeat the observations two to three times to make sure the signal we are seeing is robust and to increase the detection significance" to the level at which the odds of a statistical fluke are below roughly one in a million, Madhusudhan said. "Second, we need more theoretical and experimental studies to make sure whether or not there is another abiotic mechanism (one not involving biological processes) to make DMS or DMDS in a planetary atmosphere like that of K2-18 b. Even though previous studies have suggested them (as) robust bio signatures even for K2-18 b, we need to remain open and pursue other possibilities," Madhusudhan said. So the findings represent "a big if" on whether the observations are due to life, and it is in "no one's interest to claim prematurely that we have detected life.