Using Webb, scientists are discovering carbon dioxide and methane on exoplanets in the habitable zone | Albiseyler

Using the joint NASA/European Space Agency/Canadian Space Agency James Webb Space Telescope, scientists discovered the presence of carbon molecules in the atmosphere of the exoplanet K2-18b. These carbon-bearing molecules include methane and carbon dioxide.

The discovery of the molecules allows scientists to better understand K2-18b. The planet has been the subject of several recent studies and is believed to be a Hycean exoplanet – a planet that could have a hydrogen-rich atmosphere and a water-covered surface.

What’s more, K2-18b orbits in its parent star’s habitable zone, which is the region of space surrounding the star where the conditions are right for liquid water to form and exist. Data from NASA’s Hubble Space Telescope first hinted at the unique properties of an exoplanet’s atmosphere, which then led to multiple teams investigating the exoplanet.

K2-18b orbits the cool dwarf star K2-18 in the constellation Leo, located approximately 120 light-years from Earth and roughly 8.6 times the size of Earth. These types of exoplanets, which are between the size of Earth and Neptune, are not found in our solar system and therefore have not been studied as extensively as gas giant planets like Jupiter and Saturn.

“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. “We have obtained the most detailed spectrum of the habitable zone of the neptune to date, allowing us to detect the molecules that exist in its atmosphere,” said team member Subhajit Sarkar from Cardiff University.

Many astronomers are debating and researching the characteristics of the atmospheres of these sub-Neptunian exoplanets, with some even suggesting that under the right conditions, these planets and their atmospheres could support life.

“Our findings underscore the importance of considering different habitable environments when looking for life elsewhere. “Traditionally, the search for life on exoplanets has focused mainly on smaller rocky planets, but larger Hyckelian worlds are significantly more favorable for observing atmospheres,” said project lead author Nikku Madhusudhan from the University of Cambridge.

So, what exactly makes the K2-18 b so special?

Webb’s data on K2-18b shows the amount of methane and carbon dioxide in the exoplanet’s atmosphere. Interestingly, there is a lack of ammonia, further supporting the idea that K2-18 b could harbor a water ocean beneath its hydrogen-rich atmosphere.

In addition, Webb’s observations indicated the existence of dimethyl sulfide (DMS). Back on Earth, DMS is a molecule that only life can produce. The vast majority of all DMS molecules in the Earth’s atmosphere are formed by phytoplankton in the marine environment. However, more observations and data are needed to confirm the existence of DMS in the atmosphere of K2-18 b.

“Forthcoming Webb observations should be able to confirm whether DMS is indeed present in the atmosphere of K2-18b at significant levels,” said Madhusudhan.

Image of NIRSpec, one of the instruments that helped collect data on the spectra of K2-18b. (Credit: Astrium GmbH)

Looking at the properties and characteristics of K2-18 b, all the conditions look right for life to exist on the planet. From an exoplanet in the habitable zone to the existence of carbon-bearing molecules to the possibility of a liquid ocean on its surface, K2-18b is a perfect candidate for a habitable exoplanet. However, there are some properties of K2-18 b that could prevent it from sustaining life.

One such characteristic is the enormous size of the planet. As mentioned, K2-18b is roughly 8.6 times the size of Earth. The planet’s large size means that its interior most likely contains a large mantle of high-pressure ice, similar to Neptune’s internal structure. Additionally, K2-18b’s ocean may be too warm to be liquid or too hot to support life.

However, obtaining spectrum data on the atmosphere of K2-18 b was not without problems. The exoplanet’s parent star is very bright, meaning that light from K2-18 may have been interfering with some of Webb’s observational data.

To collect the spectral data, Webb observed K2-18 as the exoplanet crossed in front of the star – a phenomenon known as a transit. As the planet passed in front of the star, Webb recorded the star’s brightness decrease and collected data on the planet’s atmosphere as it was illuminated by the star. This data is then sent to scientists, who comb through it for signals that represent certain molecules, such as carbon dioxide.

This method of using exoplanet transits to collect atmospheric data is heavily used by exoplanet researchers. In fact, many scientists use this method of observing transits to discover exoplanets. K2-18b was discovered by NASA’s K2 mission in 2015 via a transit.

Example of a light curve generated by an exoplanet transiting its star. (Credit: NASA Ames)

“This result was only possible due to the extended wavelength range and unprecedented sensitivity of Webb, which allowed robust detection of spectral features with only two transitions. By comparison, one transit observation with Webb provided comparable accuracy to eight observations with HST made over several years and in relatively a narrow range of wavelengths,” said Madhusudhan.

Madhusudhan et al. they were able to obtain atmospheric data from just two transits of K2-18b in front of its star – again highlighting Webb’s true power and ability in exoplanet science. Webb is set to make more observations of K2-18b in the coming weeks, which will give the team even more data to comb through and hopefully discover more molecules. Specifically, the team plans to use Webb’s Mid-Infrared Instrument spectrograph for the observations.

“These results are the result of just two observations of K2-18 b, with many more on the way. This means that our work is only an early sample of what Webb can observe on exoplanets in the habitable zone,” said team member Savvas Constantinou from the University of Cambridge.

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

The results of Madhusudhan et al. were recently published in The Astrophysical Journal Letters magazine.

(Main image: Artist’s illustration of K2-18 ba and its parent star K2-18. Credit: NASA/ESA/CSA/J. Olmsted (STScI), N. Madhusudhan (Cambridge University))