"Super Earth" planet K2-18 b has an ocean and atmosphere that could support life

The James Webb Space Telescope has found evidence of carbon-bearing molecules, specifically methane and carbon dioxide, in the atmosphere of the habitable zone exoplanet K2-18 b. 

This discovery offers a new perspective on a planet that bears no resemblance to any within our own solar system. This hints at the potential for extraterrestrial habitable worlds throughout the universe.

Unique position of K2-18 b

K2-18 b, which weighs 8.6 times Earth’s mass, revolves around the cool dwarf star, K2-18. It is located 120 light-years from our planet in the constellation Leo. 

The exoplanet’s unique position between the size of Earth and Neptune designates it as a “sub-Neptune.”

Hycean exoplanet

The data from Webb suggests that K2-18 b might be classified as a Hycean exoplanet. This is an emerging category that describes planets which potentially possess hydrogen-rich atmospheres and water-covered surfaces.

According to a Webb press release, the suggestion that K2-18 b could be a Hycean exoplanet is intriguing. Some astronomers believe that these worlds are promising environments to search for evidence for life on exoplanets.

Search for alien life

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

“Traditionally, the search for life on exoplanets has focused primarily on smaller rocky planets, but the larger Hycean worlds are significantly more conducive to atmospheric observations.”

Clues in the atmosphere

The news release notes an abundance of methane and carbon dioxide, and shortage of ammonia. This supports the hypothesis that there may be a water ocean underneath a hydrogen-rich atmosphere on K2-18 b. 

The initial observations from Webb also hint at the presence of a molecule called dimethyl sulfide (DMS). On Earth, DMS is predominantly produced by life, mainly emanating from marine phytoplankton. Yet, Madhusudhan suggested that it’s crucial to approach this with caution.

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

K2-18 b is in the habitable zone 

Just because K2-18 b is in the habitable zone and showcases carbon-bearing molecules does not guarantee it can sustain life. Its vast size suggests an interior dominated by high-pressure ice, reminiscent of Neptune.

“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,” explained team member Subhajit Sarkar of Cardiff University. 

“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.”

Atmospheric composition 

The astronomers used a brilliant method to unearth these secrets. Because the parent stars of these exoplanets often outshine their smaller counterparts, it’s challenging to discern the components of these distant atmospheres. 

The team circumvented this problem by studying the light from K2-18 b’s parent star as it shone through the planet’s atmosphere. This transit method yields crucial clues about the atmospheric composition.

Webb’s remarkable precision 

“This result was only possible because of the extended wavelength range and unprecedented sensitivity of Webb, which enabled robust detection of spectral features with just two transits,” said Madhusudhan. 

“For comparison, one transit observation with Webb provided comparable precision to eight observations with Hubble conducted over a few years and in a relatively narrow wavelength range.”

“These results are the product of just two observations of K2-18 b, with many more on the way,” explained Savvas Constantinou of the University of Cambridge. “This means our work here is but an early demonstration of what Webb can observe in habitable-zone exoplanets.”

Future steps to explore K2-18 b

The research team is eager to dig deeper. Their next steps involve the MIRI (Mid-Infrared Instrument) spectrograph, aiming to further validate and enrich our understanding of K2-18 b.

“Our ultimate goal is the identification of life on a habitable exoplanet, which would transform our understanding of our place in the universe,” said Madhusudhan.

While the journey to understanding K2-18 b and other similar exoplanets has just begun, the recent discoveries underscore the importance and potential of the James Webb Space Telescope. JWST is a combined endeavor of NASA, ESA (European Space Agency), and the Canadian Space Agency.

More about the James Webb Space Telescope (JWST)

The James Webb Space Telescope (JWST) stands as humanity’s most ambitious astronomical undertaking to date. It promises to revolutionize our understanding of the universe.

NASA leads the JWST project. They are collaborating closely with the European Space Agency (ESA) and the Canadian Space Agency (CSA). Together, these agencies have developed a telescope that possesses a primary mirror nearly three times larger than Hubble’s. This increased size allows the JWST to collect more light and observe distant, ancient galaxies that have remained elusive to our current instruments.

Different than Hubble

Unlike the Hubble, which orbits Earth, the JWST will sit at the second Lagrange Point (L2), located approximately 1.5 million kilometers away from our planet. This unique position offers a stable environment, free from Earth’s radiative and light interference, enabling more detailed and clearer observations.

The JWST primarily focuses on infrared observations. This capability allows it to peer through cosmic dust clouds and witness the birth of stars and planetary systems. Additionally, by studying infrared light from the universe’s early days, the JWST aims to unravel the mysteries of the period called the “Dark Ages,” shortly after the Big Bang.

One of the JWST’s groundbreaking features is its deployable sunshield, which is the size of a tennis court. This shield protects the telescope from external heat and light, ensuring the instruments remain cool enough for accurate infrared measurements.

The James Webb Space Telescope represents the pinnacle of modern astronomical engineering and ambition. As it ventures into space, it carries humanity’s hopes and curiosities, destined to reshape our understanding of the cosmos.

The study will soon be published in The Astrophysical Journal Letters.

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