Scientists using the James Webb Space Telescope have made a potential landmark discovery. They detected in the atmosphere of an alien planet the chemical fingerprints produced by gases on Earth only through biological processes.
Webb’s observations on the planet K2-18 b were based on two gases, dimethyl sulfide (DMS) and dimethyl disulfide (DMDS), which are produced by living organisms. These include marine phytoplankton, also known as algae.
The researchers believe that this suggests the planet is teeming with microbial life. The researchers stressed that their findings are not an announcement of the discovery of living organisms, but rather of a possible biosignature – an indicator of a biological process – and that more observations should be made.
They expressed excitement. Nikku Madhusudhan, astrophysicist at the University of Cambridge Institute of Astronomy and lead author of the Astrophysical Journal Letters study, stated that these are the first signs of a possible alien world.
“This is a momentous occasion in the search for extraterrestrial life, as we have shown that biosignatures can be detected on planets that may have habitable conditions using current technology. We have entered the age of observational Astrobiology,” Madhusudhan stated.
Madhusudhan said that various efforts are underway to search for signs of life within our solar system. This includes various claims that environments on Mars, Venus, and other icy moons might be conducive for life.
K2-18b is 8,6 times the mass of Earth, and its diameter is about 2.6 times that of our planet.
It 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. One other planet has also been identified orbiting this star.
The ‘Hycean World
Since the 1990s, scientists have discovered about 5,800 exoplanets. Scientists hypothesized that exoplanets with hycean atmospheres, which are covered in a liquid ocean habitable by microorganisms, exist.
Webb, launched in 2021, became operational in 2022. Earlier observations had revealed methane in K2-18b’s atmospheric composition. This was the first time carbon-based molecules have been found in an exoplanet’s atmosphere in a habitable zone of a star.
Madhusudhan stated, “The only scenario that can explain all of the data obtained from JWST (James Webb Space Telescope), including past and current observations, is a scenario where K2-18b was a hycean planet teeming a life. We need to remain open to other scenarios and keep exploring them.”
Madhusudhan stated that hycean planets would have microbial life similar to what is found in Earth’s oceans. It is hypothesized that their oceans would be warmer than Earth’s. Madhusudhan replied that he would not be able to answer the question about multicellular life or intelligent life at this time. The assumption is that simple microbial organisms are the norm.
DMS and DMDS are both members of the same chemical family. They have been predicted to be important biosignatures on exoplanets. Webb determined that either one or both could be present in the atmosphere of the planet at a level of 99.7% confidence, which means there is still a 0.3% chance the observation was a statistical accident.
Gases were detected in concentrations greater than 10 parts per billion 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.
Scientists who were not involved in the research urged caution.
Christopher Glein is the principal scientist of the Space Science Division at Southwest Research Institute, Texas. He said, “The rich K2-18b data makes it an exciting world. The latest data makes a valuable contribution to our understanding. We must test data as thoroughly and carefully as possible. I look forward to additional independent work on data analysis beginning as early as next week.
Transit Method
K2-18b belongs to the “sub-Neptune class” of planets. It has a diameter that is greater than Earth’s but smaller than Neptune’s. Neptune is our solar system’s small gas planet.
The transit method is used by astronomers to determine the chemical composition of the atmosphere of an exoplanet. Webb detects a reduction in the brightness of the star as the planet passes by. A small portion of the starlight is then reflected through the atmosphere and detected by the telescope. Scientists can then determine what gases make up the atmosphere of the planet.
Webb’s earlier observations of this world provided a hint that DMS might exist. The new observations were made with a different light wavelength and instrument.
Madhusudhan stated that the “Holy Grail of exoplanet research” is finding evidence of life beyond our solar system on a planet similar to Earth. Madhusudhan stated that for thousands of years, our species has asked, “Are we the only ones” in the universe. Now it may be possible to detect alien life on a hycean planet.
Madhusudhan, however, still urges caution.
Madhusudhan explained that “first we need to repeat our observations two or three times to ensure the signal is robust and increase the detection significance”, to a level where the odds of a statistical fluke being below 1 in a thousand are low.
“Second,” Madhusudhan said, “We need to do more theoretical and experimental studies to determine if there’s another abiotic [abiotic means that doesn’t involve biological processes mechanism to produce DMS or DMDS on a planet with an atmosphere similar to K2-18 b. Even though previous studies suggested that they were robust biosignatures, even for K2-18b, we must remain open and explore other possibilities.”
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,” Madhusudhan said.
