Webb Space Telescope Detects Key Molecules in Exoplanet K2-18 b

The data suggests that the exoplanet has a possible liquid ocean surface.

Carbon-bearing molecules have been discovered in the atmosphere of the habitable zone extraterrestrial International Group of Astronomers using data from K2-18 b NASAs The James Webb Space Telescope. These results are consistent with an exoplanet having an ocean-covered surface beneath a hydrogen-rich atmosphere. The discovery provides a fascinating glimpse of a planet unlike any in our solar system, and raises interesting possibilities about habitable worlds elsewhere in the universe.

Spectra of K2-18 b, obtained with Webb’s NIRISS (Near-Infrared Imager and Slitless Spectrograph) and NIRSpec (Near-Infrared Spectroscopy), show abundant methane and carbon dioxide in the exoplanet’s atmosphere, as well as a possible detector molecule called dimethyl sulfide (DMS). The detection of methane and carbon dioxide and the lack of ammonia support the hypothesis that K2-18 b may have a water ocean beneath the hydrogen-rich atmosphere. K2-18 b, 8.6 times larger than Earth, orbits the cool dwarf star K2-18 in the habitable zone and is 120 light-years from Earth. Credit: NASA, ESA, CSA, Ralf Crawford (STScI), Joseph Olmsted (STScI), Nikku Madhusudhan (IoA)

K2-18 Webb discovered methane and carbon dioxide in the atmosphere

K2-18b, an exoplanet 8.6 times the size of Earth, was discovered by NASA’s James Webb Space Telescope to reveal carbon-bearing molecules including methane and carbon dioxide. Webb’s discovery adds to recent studies suggesting that K2-18 b may be a Hyssian exoplanet, with a hydrogen-rich atmosphere and a water ocean-covered surface.

The first insight into the atmospheric properties of this habitable-zone exoplanet came from observations by NASA’s Hubble Space Telescope.

K2-18 b orbits the cool dwarf star K2-18 in the habitable zone and is 120 light-years from Earth in the constellation Leo. Exoplanets, such as K2-18 b, are Earth-sized and Neptune, unlike anything in our solar system. Because there are no nearby equivalent planets, these ‘sub-Neptunes’ are poorly understood, and the nature of their atmospheres is the subject of intense debate among astronomers.

Implications for Exoplanet Life

The idea that sub-Neptune K2-18 b might be a Hyssian exoplanet is intriguing, and some astronomers believe these worlds are promising environments for searching for evidence of life on exoplanets.

“Our findings underscore the importance of considering a variety of habitable environments in the search for life elsewhere,” said Nikku Madhusudhan, an astronomer at the University of Cambridge and lead author of the paper announcing these results. are optimal.”

The presence of methane and carbon dioxide and the lack of ammonia support the hypothesis that a water ocean may exist beneath the hydrogen-rich atmosphere in K2-18 b. These early web observations also provided the possible detection of a molecule called dimethyl sulfide (TMS). On Earth, it is produced only by life. Most of the DMS in Earth’s atmosphere is emitted from phytoplankton in the marine environment.

The assumption of DMS is less robust and requires further verification.

“Upcoming web observations could confirm that DMS is indeed present in significant amounts in the atmosphere of K2-18 b,” explained Madhusudhan.

Characteristics of exoplanet atmospheres

K2-18 b is in the habitable zone and is now known to contain carbon-bearing molecules, which do not necessarily mean the planet could support life. The planet’s large size — 2.6 times the radius of Earth — means the planet’s interior may have high-pressure ice like Neptune, but a thin hydrogen-rich atmosphere and oceanic surface. Hyssian worlds are predicted to have oceans of water. However, 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 so far in the galaxy,” explained team member Subhajit Sarkar of Cardiff University. “We obtained the most comprehensive spectrum of habitable-zone sub-Neptune to date, and this allowed us to model the molecules present in its atmosphere.”

Characterizing the atmospheres of exoplanets like K2-18 b — that is, identifying their gases and physical states — is a very active area of ​​astronomy. However, the glare of these planets from their more massive parent stars makes probing exoplanet atmospheres particularly challenging.

The team sidestepped this challenge by analyzing the light from K2-18 b’s parent star as it passes through the exoplanet’s atmosphere. K2-18 b is a transiting exoplanet, which means we can detect a decrease in brightness as it passes across the face of its host star. The exoplanet was first discovered by NASA’s K2 mission in 2015. This means that a small fraction of the starlight during transit passes through the exoplanet’s atmosphere before reaching telescopes like Webb’s. The passage of starlight through an exoplanet’s atmosphere leaves traces that astronomers can piece together to determine the gases of the exoplanet’s atmosphere.

James Webb’s abilities and future research

“This result was only possible due to the extended wavelength range and the unprecedented sensitivity of the web, which enabled robust detection of spectral features with two transits,” said Madhusudhan. “For comparison, one transit observation with Webb provided comparable precision to eight observations conducted with Hubble over a relatively narrow wavelength range.”

“These results are the result of two observations of K2-18 b, with many more to come,” explained team member Savvas Constantino of the University of Cambridge. “Our work here is an early demonstration of what the WEB can observe in habitable-zone exoplanets.”

The results of the panel were accepted for publication in The Astrophysical Journal Letters.

The team now plans to carry out further research with the telescope’s MIRI (Mid-Infrared Instrument) spectrograph, which they hope will further validate their findings and provide new insights into environmental conditions on K2-18 b.

“Our ultimate goal is to identify life on a habitable exoplanet, which will change our understanding of our place in the universe,” concluded Madhusudhan. “Our findings are a promising step in this quest for a deeper understanding of Hyssian worlds.”

NASA’s James Webb Space Telescope is the world’s premier space science laboratory. It solves the mysteries of our solar system, looks beyond to distant worlds around other stars, and probes the mysterious structures and origins of our universe and our place in it. WEB is an international project led by NASA’s partners, ESA.European Space Agency) and the Canadian Space Agency.