In an exhilarating leap forward in the quest for extraterrestrial life, scientists have uncovered compelling evidence of a gas that is typically produced exclusively by living organisms. The discovery was made on K2-18 b, a distant exoplanet located 120 light-years away from Earth. This ‘super Earth,’ more than eight times the size of our planet, orbits a cool dwarf star within the habitable zone of the Leo constellation. It has earned the classification of a ‘Hycean’ world due to its hydrogen-rich atmosphere and substantial water oceans, making it an enticing prospect for the search for alien life.
What has truly ignited the scientific community’s excitement is the detection of dimethyl sulphide (DMS) in the planet’s atmosphere. DMS is a complex molecule composed of carbon, hydrogen, and sulfur atoms, and on Earth, it is exclusively produced by living organisms, primarily phytoplankton in marine environments. NASA characterized the revelation as a “mix of shock and excitement and disbelief.” This discovery is indeed tantalizing, but scientists are cautious and emphasize that further observations by the James Webb Space Telescope are necessary to confirm the presence of DMS.
Should this discovery be validated, K2-18 b could rank among the most promising candidates for hosting alien life, alongside celestial bodies like Mars and the icy moons of Jupiter and Saturn within our own solar system. The exoplanet’s atmosphere also contains significant amounts of carbon dioxide and methane, which, while promising, do not independently confirm the presence of alien life as these gases can be generated through inorganic processes.
Lead researcher Nikku Madhusudhan from the University of Cambridge expressed the awe-inspiring nature of this revelation, particularly the potential existence of DMS on a distant exoplanet. He stated, “Our discovery is a major development in exoplanetary science, particularly the demonstration that we can detect carbon-based molecules in low-mass exoplanets in the habitable-zone.” Madhusudhan also highlighted the significance of forthcoming observations from the James Webb Space Telescope in affirming the presence of DMS on K2-18 b.
NASA’s observatory, with a budget of $10 billion (£7.4 billion), possesses the capability to analyze the chemical composition of a distant planet by analyzing the light from its host star as it passes through the planet’s atmosphere and reaches Earth. Gases in the atmosphere absorb specific wavelengths of starlight, leaving distinctive spectral signatures that astronomers can decipher.
K2-18 b, classified as both a ‘super Earth’ and a ‘sub-Neptune,’ offers unique insights into the diversity of exoplanets. Sub-Neptunes, planets that do not exist in our solar system, have a smaller radius than the farthest ice giant from the sun. These intriguing worlds, although poorly understood due to their distance from us, have atmospheres that continue to puzzle astronomers. K2-18 b’s substantial size, with a radius 2.6 times that of Earth, suggests an interior mantle of high-pressure ice akin to Neptune. This, coupled with a thinner hydrogen-rich atmosphere and a water-covered surface, characterizes it as a Hycean world. However, it remains uncertain whether the ocean is hospitable or even liquid due to potential extreme temperatures.
For over three decades, scientists have been discovering exoplanets beyond our solar system, with thousands identified to date. Many of these exoplanets fall into the category of ‘super Earths,’ ‘mini-Neptunes,’ or ‘sub-Neptunes,’ indicating a range of sizes and atmospheres. While initial studies suggested that the high pressure and temperature beneath their hydrogen-rich atmospheres rendered these worlds uninhabitable, recent research has unearthed conditions that could support life under certain circumstances.
In addition to verifying the presence of DMS on K2-18 b, researchers will now explore the potential existence of other biomarkers, such as methyl chloride, which are uniquely generated by living organisms. The confirmation of such biomarkers would propel K2-18 b to the forefront of the search for alien life, marking an exciting new chapter in the quest to answer one of humanity’s most profound questions: Are we alone in the universe?