This article was originally published in English
Astronomers are searching for signs of life elsewhere in the universe, with the planet K2-18 b of particular interest. Researchers remain cautious.
The James Webb Space Telescope may have discovered a molecule in the atmosphere of a distant exoplanet that is only produced by life on Earth, according to NASA.
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The planet K2-18 b has been the subject of extensive study since astronomers announced in 2019 that they had found potential signs of water vapor in its atmosphere.
The planet orbits a red dwarf star in the constellation Leo, about 120 light-years from our solar system, and has a mass 8.6 times that of Earth.
A later study using the same data then suggested that the water vapors could actually be methane.
Now the even more powerful James Webb Telescope has turned its attention to the planet, providing a wealth of new data.
He discovered the presence of carbon-containing molecules, including methane and carbon dioxide, fueling speculation that K2-18 b may have a hydrogen-rich atmosphere and a surface covered by an ocean of water.
These features could be signs that there is life on the planet.
Clues to life?
James Webb’s observations included the possible detection of a molecule called Dimethyl sulfide (DMS), which is only produced by life on our planet.
Most of the DMS in Earth’s atmosphere comes from phytoplankton, microscopic organisms found in the oceans.
In a statement, NASA said the hypothesis about the presence of DMS in the atmosphere was “less robust” than other results and requires further validation.
“The upcoming observations from the Webb spacecraft should help confirm whether DMS is indeed present in significant quantities in the atmosphere of K2-18 b,” says Nikku Madhusudhan, an astronomer at the University of Cambridge and lead author of the paper describing this Results will be announced.
However, the space agency clarified that the abundance of methane and carbon dioxide found in the atmosphere, as well as the lack of ammonia, support the hypothesis of the existence of an ocean of water beneath the hydrogen-rich atmosphere of K2-18 b.
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The planet is believed to be an example of a Hycean planet, a planet larger than Earth but smaller than the gas giants of our solar system and covered by a liquid ocean and a thick nitrogen atmosphere.
There are no planets like K2-18 b in our solar system. They are therefore poorly known, although scientists believe they are common near red dwarfs.
Some astronomers believe Hycaean planets could be promising environments for searching for traces of life.
“Our results underscore the importance of considering different habitable environments when searching for extraterrestrial life,” emphasizes Nikku Madhusudhan.
“Traditionally, the search for life on exoplanets has focused primarily on small, rocky planets, but the larger Hycean planets are much more suitable for atmospheric observations.”
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Exoplanet in habitable zone
Astronomers are particularly interested in studying K2-18 b because it is also in the habitable zone of its host star, meaning it is neither too close nor too far from its sun.
However, NASA points out that despite the apparent composition of its atmosphere and its proximity to its star, the planet’s size means its interior likely contains a vast mantle of high-pressure ice, like Neptune, but with a finer and finer atmosphere rich in hydrogen and a sea surface.
The space agency says that while Hycaean planets are thought to have oceans of water, it is also possible that the ocean is too hot to be habitable or liquid.
“Although this type of planet does not exist in our solar system, sub-Neptunes are the most common type of planet known to date in the galaxy,” says university team member Subhajit Sarkar from Cardiff.
“We obtained the most detailed spectrum to date of a habitable zone beneath Neptune and were able to determine the molecules present in its atmosphere.”
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Measuring the atmosphere
Studying the possible atmospheric composition of an exoplanet is a difficult task, especially since the host star is much brighter than the planet itself.
Astronomers were able to analyze K2-18 b by observing how light from its parent star passed through the planet’s atmosphere. As the planet passes in front of the star, telescopes can detect the drop in brightness that occurs at that time.
This is a common technique for detecting the presence of a planet around a star, but also results in the emission of light through the planet’s atmosphere, light that can also be captured by telescopes as powerful as James Webb.
By studying this light, experts can determine some of the gases that make up the exoplanet’s atmosphere. “This result was only possible thanks to the extended wavelength range and unprecedented sensitivity of the Webb telescope, which enabled robust detection of spectral features with just two transits,” assures Nikku Madhusudhan.
“For comparison, a transit observation with James Webb provided comparable precision to eight Hubble observations carried out over several years and in a relatively narrow wavelength range.”
The researchers added that this is just the beginning of the James Webb Telescope observations and that there are “many more to come.”
Her Results were published in the Astrophysical Journal Letters.
The team now intends to conduct further research using the telescope’s MIRI (Mid-Infrared Instrument) spectrograph. She hopes this research will further validate her results and provide new information about the environmental conditions of K2-18 b.