Astronomers yesterday announced that they had detected the most promising “hints” of potential life on a planet beyond our solar system, although other scientists expressed skepticism.
There has been debate in scientific circles about whether the planet K2-18b, which is 124 light-years away in the Leo constellation, could be an ocean world capable of hosting microbial life.
Using the James Webb Space Telescope, a British-US team of researchers detected signs of two chemicals in the planet’s atmosphere long considered to be “biosignatures” indicating extraterrestrial life.
An artist’s impression released on Sept. 11, 2019, by the European Space Agency and Hubble depicts the K2-18b exoplanet, right, orbiting its sun.
On Earth, the chemicals dimethyl sulfide (DMS) and dimethyl disulfide are produced only by life, mostly microscopic marine algae called phytoplankton.
The researchers emphasized caution, saying that more observations were needed to confirm the findings and that they were not announcing a definitive discovery.
However, the implications could be huge, said Nikku Madhusudhan, a University of Cambridge astrophysicist and lead author of the study published in The Astrophysical Journal Letters.
“What we are finding at this point are hints of possible biological activity outside the solar system,” Madhusudhan told a news conference. “Frankly, I think this is the closest we have come to seeing a feature that we can attribute to life.”
However, outside experts pointed to disputes over previous discoveries about the exoplanet, adding that the chemicals could have been created by unknown means having nothing to do with life.
More than eight times the mass of Earth and 2.5 times as big, K2-18b is a rare exoplanet that orbits its star in a habitable or “goldilocks” zone.
This means it is neither too hot nor too cold to have liquid water, considered the most important ingredient for life.
Telescopes observe such far-off exoplanets when they cross in front of their star, allowing astronomers to analyze how molecules block the light streaming through their atmosphere.
In 2023, the Webb telescope detected methane and carbon dioxide in K2-18b’s atmosphere, the first time such carbon-based molecules were detected on an exoplanet in a habitable zone.
It also detected weak signals of DMS, leading astronomers to turn Webb toward the planet again a year ago, this time using its mid-infrared instrument to detect different wavelengths of light.
They found much stronger signs of the chemicals, although still well below the “five sigma” threshold of statistical significance scientists seek for such discoveries.
Even if the results are confirmed, it would not necessarily mean that the planet is home to life.
Last year, scientists found traces of DMS on a comet, which suggested it can be produced in non-organic ways.
However the concentration of the chemical observed on K2-18b appears to be thousands of times stronger than levels on Earth, strongly suggesting a biological origin, Madhusudhan said.
K2-18b has long been considered the premier candidate for a “hycean planet” — an ocean world bigger than Earth with a hydrogen-rich atmosphere.
These planets would not be expected to be home to intelligent alien life, but rather tiny microbes.
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