K2-18b Offers Strongest Clue Yet of Extraterrestrial Life
Scientists from the University of Cambridge have identified potential biosignatures on K2-18b. This exoplanet lies 124 light-years away in the constellation Leo. The team used NASA’s James Webb Space Telescope for the observations. They found dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) in the planet’s atmosphere. These chemicals are only made by biological life on Earth.
Figure 1: Illustration shows what K12-18b could look like based on science data
Discovery Signals New Era in Astrobiology
Lead researcher Dr Nikku Madhusudhan from Cambridge’s Institute of Astronomy led the study. The findings were published in the Astrophysical Journal Letters. “This is a transformational moment in the search for life beyond the solar system,” Madhusudhan said. He added, “We have demonstrated that it is possible to detect biosignatures in potentially habitable planets with current facilities.” Scientists have entered what he called “the era of observational astrobiology.”
DMS and DMDS Indicate Potential Microbial Life
On Earth, DMS and DMDS are primarily produced by marine phytoplankton. The team estimated their concentrations on K2-18b exceed 10 parts per million. Earth’s atmospheric concentration remains below 1 part per billion by volume. Madhusudhan noted, “For reference, this is thousands of times higher than their concentrations in the Earth’s atmosphere.” He said, “They cannot be explained without biological activity based on existing knowledge.”
Cautious Optimism in Scientific Community
Despite the strong findings, scientists remain cautious about concluding the presence of life. “It is in no one’s interest to claim prematurely that we have detected life,” Madhusudhan said. He stressed the need for more theoretical and experimental studies. The team aims to test if abiotic processes could produce these molecules. “We need to remain open and pursue other possibilities,” he said. The confidence level for detecting these gases stood at 99.7 per cent. This leaves a 0.3 per cent chance the result is a statistical fluke.
Next Steps in Confirming the Signal
Madhusudhan outlined a two-step approach moving forward. First, the team plans to repeat the observations two to three times. This would help confirm the robustness of the signal. Second, they intend to study potential non-biological sources of DMS and DMDS. “We can confirm this signal within one to two years,” Madhusudhan told the BBC.
Planet K2-18b Located in Star’s Habitable Zone
K2-18b orbits a red dwarf star that is smaller and cooler than the Sun. The planet lies in the star’s habitable zone. This is the region where liquid water can exist on the surface. K2-18b is 8.6 times more massive than Earth and 2.6 times its size. It belongs to the “sub-Neptune” class of planets. These planets have a diameter between Earth’s and Neptune’s. The exoplanet was first discovered in 2015.
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Scientists Classify K2-18b as a Hycean World
Earlier observations in 2019 detected water vapour in K2-18b’s atmosphere. This supported the possibility of a “Hycean” world. A Hycean planet is covered by a liquid ocean and has a hydrogen-rich atmosphere. Scientists believe such worlds can host microbial life in their oceans. “The only scenario that currently explains all the data obtained so far… is one where K2-18 b is a hycean world teeming with life,” Madhusudhan said. He noted, “We are talking about microbial life, possibly like what we see in the Earth’s oceans.”
Webb Telescope Advances Exoplanet Research
The James Webb Space Telescope launched in December 2021 and became operational in 2022. It offers the deepest look into space ever captured. It helped detect DMS and DMDS using the transit method. This method analyses starlight filtered through the planet’s atmosphere during transit. Webb previously detected carbon dioxide and methane on K2-18b. These findings were the first to detect carbon-bearing molecules in a habitable zone exoplanet.
Other Experts Urge Thorough Data Validation
External experts welcomed the findings but advised caution. “The rich data from K2-18 b make it a tantalising world,” said Christopher Glein from the Southwest Research Institute in Texas. He said, “These latest data are a valuable contribution to our understanding.” Glein added, “Yet, we must be very careful to test the data as thoroughly as possible.” Independent analyses are expected to begin soon.
Search for Life Beyond Earth Gains Momentum
The detection of possible biosignatures marks progress in astrobiology. “This is the strongest evidence yet there is possibly life out there,” Madhusudhan said. He noted, “We won’t be able to answer this question at this stage,” when asked about intelligent life. The focus remains on microbial organisms. “First we need to repeat the observations… to increase the detection significance,” he said. The scientific community continues to pursue the question of habitability with rigorous scrutiny.
