This week has been a big leap for science. With the help of the James Webb Space Telescope (JWST), scientists have detected the presence of at least one of two molecules of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) in the atmosphere of the distant planet K2-18b, located some 124 light years away. DMS and DMDS molecules are associated with life, and on our home planet, these gases are produced by bacteria and marine phytoplankton.
While the discovery has not offered definitive proof of life, Professor Nikku Madhusudhan from the Institute of Astronomy at University of Cambridge who led the research told the BBC that he hopes to obtain more substantial evidence soon. K2-18b is a sub-Neptune exoplanet that is located within its star, the red dwarf K2-18. Even though the presence of either DMS or DMDS suggests the planet could support life, scientists are working through alternative non-biological explanations. Researchers feel that there is a need for further observations and analyses to confirm these findings and rule out other sources of these compounds.
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
In June 2023, it was reported that Nasa’s Cassini mission, carried out to explore Saturn and its moons between 2004 and 2017, gave significant insights about Enceladus, one of the planet’s moons. Reportedly, in 2005, Cassini discovered plumes of vapour and ice particles emanating from Enceladus’s south pole. This indicated the presence of a subsurface ocean; subsequent flybys traced organic molecules, carbon dioxide, methane, and molecular hydrogen in these plumes. According to researchers, this suggested hydrothermal activity on the ocean floor. All of these pointed to the possibility that Enceladus’s ocean may be habitable.
Scientists also reported the detection of phosphates in the icy grains emitted by Enceladus, essentially getting closer to the list of key elements needed for life. In December 2023, the discovery of hydrogen cyanide and other organic molecules in the plumes further backed the claim of the moon’s potential to foster life.
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.
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Presence/absence of phosphine on Venus
In September 2020, scientists at MIT, Cardiff University and others observed that there may be signs of life in the clouds of Venus. Although there was no direct evidence suggesting living organisms, astronomers led by Jane Greaves detected a spectral fingerprint or light-based signature of phosphine, a gas that is associated with living organisms. Back then the researchers had made the detection with the help of the James Clerk Maxwell Telescope (JCMT) in Hawaii and the Atacama Large Millimetre Array (ALMA) observatory in Chile.
Phosphine is usually produced by anaerobic microorganisms on Earth, which also makes it a potential biosignature. This discovery made headlines, as Venus was typically known to have extreme conditions on its surface. However, in November 2022, Nasa’s Stratospheric Observatory for Infrared Astronomy (SOFIA), an airborne observatory system, claimed that Venus does not have any obvious phosphine. Other studies also suggested that the spectral signals attributed to phosphine may have been misidentified. As of now the presence of phosphine on Venus remains unconfirmed.
Jupiter’s moon Europa has oceans?
The largest planet in our solar system, Jupiter, has 95 moons as of 2024. The largest are the Galilean moons – Io, Europa, Ganymede and Callisto. Over the years, Europa has been a strong contender for scientists who have been searching for extraterrestrial life within the solar system. There has been some convincing evidence that Europa is home to a subsurface ocean beneath its icy crust. According to data from Nasa’s Galileo mission, there have been disruptions in Jupiter’s magnetic field around Europa hinting at the presence of an electrically conductive layer which could most likely be a global ocean of salty water under the surface.
Subsequent observations detected water vapour plumes being emitted from Europa’s surface. The US space agency launched the Europa Clipper spacecraft in October 2024 to probe Europa’s habitability. The mission is slated to arrive in Jupiter in 2030 and aims to conduct detailed recce of Europa’s ice shell and underlying ocean, assess its composition and search for signs of geological activity. The mission will help determine if Europa possesses the conditions, such as liquid water, key chemical elements, and energy sources, needed to support life.