Scientists have made an exciting and potentially groundbreaking discovery in the search for alien life. They’ve detected signs of a gas produced only by living organisms on a distant water planet known as K2-18 b.
This exoplanet, over eight times the size of Earth and located 120 light-years away in the Leo constellation, sits within the habitable zone of its cool dwarf star.
It’s classified as a ‘Hycean’ world, a relatively new type of exoplanet with hydrogen-rich atmospheres and water oceans, making it conducive to potential alien life.
Astronomers are even more excited by the presence of a gas “uniquely associated with life” on K2-18 b. This exoplanet, often referred to as a ‘super Earth’ due to its size larger than ours but smaller than Neptune, has this remarkable gas detected in its atmosphere, sparking further intrigue.
The compound dimethyl sulphide (DMS), a complex molecule composed of carbon, hydrogen, and sulfur atoms, was identified in conjunction with two carbon-carrying gases, evoking a blend of astonishment, excitement, and disbelief among researchers.
NASA emphasized that on Earth, DMS is exclusively generated by living organisms, with a significant portion emanating from marine phytoplankton.
Despite the excitement, scientists emphasized the necessity for additional observations by the James Webb Space Telescope to confirm the presence of DMS.
If validated, this discovery would place K2-18b among the most promising candidates for the existence of alien life, alongside celestial bodies such as Mars and the icy moons of Jupiter and Saturn within our own solar system.
Furthermore, K2-18b was found to possess substantial amounts of carbon dioxide and methane in its atmosphere, suggesting potential habitability or even current habitation. While this strongly indicates K2-18b’s classification as a ‘Hycean’ world, it’s essential to note that both gases can also be produced by inorganic processes and do not constitute definitive proof of extraterrestrial life on their own.
Nikku Madhusudhan, the lead author of the study, expressed profound amazement at the prospect of DMS existing on a distant exoplanet, hailing this discovery as a major breakthrough in exoplanetary science. He further underscored the significance of inferring the possibility of an ocean on this distant planet.
‘When we first saw the data it was a very exciting and surreal experience to be making such a fundamental discovery.’
Professor Madhusudhan also noted, ‘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.
‘Upcoming Webb observations should be able to confirm if DMS is indeed present in the atmosphere of K2-18 b at significant levels.’
NASA’s $10 billion observatory has the capability to analyze the chemical composition of a distant planet by capturing the light from its host star as it passes through the planet’s atmosphere on its way to Earth. Gases in the atmosphere absorb specific portions of the starlight, each leaving distinct signatures in the spectrum of light. Astronomers can then decipher these signatures to gather crucial information.
In addition to being referred to as a super Earth, K2-18b is also categorized as a ‘sub-Neptune’ planet.
These types of planets are not present in our own solar system and are defined as planets with a smaller radius than the ice giant farthest from the sun. Sub-Neptunes remain enigmatic due to their considerable distance from us, leading to ongoing debates among astronomers regarding the nature of their atmospheres.
Subhajit Sarkar, a researcher at Cardiff University, remarked, “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.”
K2-18b’s substantial size, with a radius 2.6 times that of Earth, suggests that the planet likely possesses a substantial mantle of high-pressure ice within, akin to Neptune. However, it sports a thinner hydrogen-rich atmosphere and a surface covered by an ocean.
While Hycean worlds are theorized to be covered in water, there is the possibility that the ocean may be too hot to support life or remain in a liquid state.
The discovery of the first exoplanet occurred 30 years ago, and since then, thousands of exoplanets have been detected outside our solar system. Many of these exoplanets fall into the category of super-Earths, mini-Neptunes, or sub-Neptunes, with a wide range of compositions from predominantly rocky to ice giants with hydrogen-rich atmospheres, or something in between.
Previous studies suggested that the high pressure and temperature beneath the hydrogen-rich atmospheres of such planets would make them inhospitable for life. However, in 2021, research indicated that under specific conditions, these worlds could potentially support life.
In addition to confirming the presence of DMS on K2-18b, researchers will also be searching for other biomarkers, such as methyl chloride, which are produced uniquely by living organisms. The discovery of such biomarkers would generate significant excitement and propel K2-18b to the forefront of the search for extraterrestrial life.
Habitable Hycean Worlds: An interview with Dr. Nikku Madhusudhan
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