Science has made significant progress this week. Scientists have discovered that the atmosphere of the far-off planet K2-18b, which is about 124 light years away, has at least one of the two molecules of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS), thanks to the James Webb Space Telescope (JWST). On our home planet, microorganisms and sea phytoplankton produce the DMS and DMDS chemicals that are linked to life.
Professor Nikku Madhusudhan of the University of Cambridge’s Institute of Astronomy, who oversaw the study, told the BBC that he hopes to soon have more solid evidence, even though the discovery has not provided conclusive confirmation of life. Within its star, the red dwarf K2-18, lies the sub-Neptune exoplanet K2-18b. Scientists are considering other non-biological causes, despite the fact that the presence of either DMS or DMDS indicates the planet may host life. To validate these results and rule out alternative origins of these chemicals, researchers believe more observations and analysis are necessary.
The latest development is testament to the remarkable capabilities of JWST in studying exoplanets. It is a significant milestone in the quest seeking life outside Earth. Beyond the recent discovery, here is a list of five notable instances when scientists discovered potential evidence or predicted life outside Earth.
Methane and carbon dioxide in the atmosphere of K2-18 b
Based on a paper published in September 2023, a team of astronomers led by the University of Cambridge spotted methane and carbon dioxide in the atmosphere of K2-18b. This was the first time carbon-based molecules were found in this planet’s atmosphere, and it hinted at a possibility that it could support life. Reportedly, K2-18b is 8.6 times the mass of Earth and lies some 124 light years away in the Leo constellation. This observation followed earlier citations by the Hubble Space Telescope that suggested a hydrogen-rich atmosphere; however, its exact composition was uncertain. According to the data from the paper, JWST confirmed the presence of these gases, also hinting at an ocean-covered surface. Back then too, researchers had found signs of DMS, the molecule linked to life on Earth; however, it was unconfirmed. The K2-18b is a part of a category of planets known as Hycean worlds – planets that are potentially habitable.
Building blocks for life on Saturn’s moon
According to a June 2023 article, NASA’s Cassini mission, which was conducted between 2004 and 2017 to study Saturn and its moons, provided important new information about one of the planet’s moons, Enceladus. According to reports, Cassini found ice and vapor plumes originating from the south pole of Enceladus in 2005. Subsequent flybys detected organic compounds, carbon dioxide, methane, and molecular hydrogen in these plumes, indicating the existence of a subsurface ocean. This indicated hydrothermal activity on the ocean floor, experts said. These all suggested that the ocean on Enceladus might be habitable.
Additionally, phosphates were found in the frozen grains that Enceladus exhaled, bringing the list of necessary ingredients required for life one step closer. The idea that the moon could support life was further supported in December 2023 when hydrogen cyanide and other organic compounds were found in the plumes.
Ancient habitability on Mars
Earlier this year, Nasa’s Curiosity rover offered some convincing evidence of the red planet’s ancient habitability. This was suggested with the discovery of well-preserved wave ripples in the Gale Crater region of the planet. These geological features were formed some 3.7 billion years ago. They indicate the presence of shallow, ice-free lakes on the surface of Mars. Scientists said that the symmetrical ripples found in two distinct rock layers hinted that the lakes were open to the atmosphere and were influenced by waves driven by winds. This also implies that the planet may have had warmer temperatures than previously thought. Incidentally, this discovery also extended the timeline during which liquid water, and potentially life, may have occurred on the red giant. An extension to this, Curiosity rover identified large amounts of the mineral siderite in rock samples from Gale Crater this month. According to scientists, siderite forms in environments that are rich in carbon dioxide, hinting that Mars may have once had a green-gas-enriched atmosphere.
Presence/absence of phosphine on Venus
Scientists from Cardiff University, MIT, and other institutions noted in September 2020 that there might be evidence of life in Venus’ clouds. Astronomers under the direction of Jane Greaves discovered a spectral fingerprint or light-based signature of phosphine, a gas linked to live things, despite the lack of concrete evidence pointing to the presence of living things. The Atacama Large Millimetre Array (ALMA) observatory in Chile and the James Clerk Maxwell Telescope (JCMT) in Hawaii assisted the researchers in making the discovery back then.
Phosphine is a possible biosignature because it is typically formed by anaerobic microbes on Earth. Since Venus was known for having harsh conditions on its surface, this discovery made news. But in November 2022, NASA’s airborne observatory system, the Stratospheric Observatory for Infrared Astronomy (SOFIA), asserted that there is no visible phosphine on Venus. The spectral signals ascribed to phosphine might have been misdiagnosed, according to other research. The existence of phosphine on Venus has not yet been verified.
Jupiter’s moon Europa
As of 2024, Jupiter, the largest planet in our solar system, had 95 moons. The Galilean moons—Io, Europa, Ganymede, and Callisto—are the biggest. For scientists looking for extraterrestrial life in the solar system, Europa has been a serious contender over the years. Some compelling evidence has suggested that beneath Europa’s frozen surface is an ocean. Data from NASA’s Galileo mission indicates that Jupiter’s magnetic field has been disrupted around Europa, suggesting the existence of an electrically conductive layer that is most likely a worldwide ocean of salty water beneath the surface.
Later observations revealed plumes of water vapor emanating from the surface of Europa. In order to investigate if Europa is habitable, the US space agency launched the Europa Clipper mission in October 2024. The mission, which is scheduled to land on Jupiter in 2030, intends to perform a thorough reconnaissance of Europa’s ocean and ice shell, evaluate its composition, and look for indications of geological activity. The mission will assist in determining whether Europa has the necessary ingredients, energy sources, liquid water, and other requirements to support life.