An International Team of Astronomers using data from NASA’s James Webb Space Telescope (JWST) discovered carbon-bearing molecules on K2-18b, a potentially habitable exoplanet on 11th September.[1]
Exoplanet K2-18b is about 8.6 times the size of Earth and is a transiting exoplanet, which means that we can detect a drop in brightness as it passes across the face of its host star.
This was how the exoplanet was first discovered in 2015 with NASA’s K2 mission, by the Kepler Space Telescope, and its existence was later confirmed by the Spitzer Space Telescope and Doppler velocity techniques.
Earlier in 2019, observations from the Hubble Space Telescope[2] revealed that the planet orbiting a cool red dwarf star resides in the habitable zone or the Goldilocks Zone, of its red dwarf star and water vapor signatures have been found from its atmosphere.
Findings of the Research on Exoplanet K2-18b
Earlier observations from the Hubble Space Telescope hinted at the possibility that—if confirmed with future studies—this could be the only exoplanet known to have both water in its atmosphere and temperatures that could sustain liquid water on a rocky surface.
Liquid water would only be possible if the planet turns out to be terrestrial, which would imply that it has a solid surface and atmosphere just like Earth, rather than resembling a small version of Neptune, implying a gaseous exoplanet.
The latest observations from NASA’s JWST indicate the presence of carbon-bearing molecules including methane and carbon dioxide.
This also leads to a possibility that K2-18b could be a Hycean exoplanet, which means a hydrogen-rich atmosphere and a water-ocean-covered surface on the planet.
JWST’s current observations reveal the presence of methane and carbon dioxide in abundance and a shortage of ammonia.
Ammonia is produced naturally in the human body and in nature by the anaerobic decay of plant and animal matter, and it’s poisonous, so high amounts of ammonia is toxic for most Earth-based life forms.
So these observations support the hypothesis that there may be a water ocean underneath a hydrogen-rich atmosphere in K2-18b.
These initial Webb observations also provided a possible detection of a molecule called dimethyl sulfide (DMS).
On Earth, this is only produced by life, and most of the DMS in Earth’s atmosphere is emitted from phytoplankton in marine environments, including some bacteria and fungi which can also produce DMS as a metabolic byproduct
On Earth, DMS plays a dual role—it contributes to the sulfur cycle and influences climate.
Produced by marine phytoplankton, DMS gets released into the atmosphere where it oxidizes into sulfate particles.
These particles act as cloud condensation nuclei, influencing cloud formation and, consequently, climate regulation.
What do Experts Say? Is there Life on K2-18b?
K2-18b is now known to house carbon-bearing molecules, but this does not necessarily mean that the planet can support life and not forget the unclear environmental conditions of the planet, it could be hostile as suggested by Hubble’s observations.
With a large size of a radius 2.6 times the radius of Earth, it’s likely that the planet’s interior contains a large mantle of high-pressure ice, like Neptune, but with a thinner hydrogen-rich atmosphere and an ocean surface.
Hycean worlds are predicted to have oceans of water, but it is also possible that the ocean is too hot to be habitable or liquid.
“Although this kind of planet does not exist in our solar system, sub-Neptunes are the most common type of planet known so far in the galaxy,” “We have obtained the most detailed spectrum of a habitable-zone sub-Neptune to date, and this allowed us to work out the molecules that exist in its atmosphere.”
Explains team member Subhajit Sarkar of Cardiff University
The team is aiming to conduct a follow-up research hoping that they will further validate their findings and provide new insights into the environmental conditions on K2-18b.
The next round of Webb observations will use the telescope’s Mid-InfraRed Instrument spectrograph to scour K2-18b’s atmosphere for tell-tale chemical signatures called biomarkers, including DMS, which could potentially indicate the presence of biological activity.
“Our ultimate goal is the identification of life on a habitable exoplanet, which would transform our understanding of our place in the Universe,” “Our findings are a promising first step in this direction.”
Nikku Madhusudhan, Astronomer at the University of Cambridge and lead author of the paper announcing the results.
References
- Nikku Madhusudhan, Subhajit Sarkar et al., Carbon-bearing Molecules in a Possible Hycean Atmosphere, NASA, 11 September 2023, https://www.nasa.gov/goddard/2023/webb-discovers-methane-carbon-dioxide-in-atmosphere-of-k2-18b[↩]
- Hubble Site, NASA’s Hubble Finds Water Vapor on Habitable-Zone Exoplanet for the First Time, 13 September 2019, https://hubblesite.org/contents/news-releases/2019/news-2019-50[↩]
