2 weeks Ago
“It’s life, Jim, but not as we know it!” is often misattributed to either Mr Spock or Dr Leonard ‘Bones’ McCoy from Star Trek. The idea of intelligent, alien life and the quest to find life beyond Earth has captivated scientists and the public alike for centuries. Recent discoveries have reignited this fascination, particularly with the detection of potential biosignatures on the exoplanet K2-18b.
The planet is approximately 124 light-years away (700 trillion miles) in the constellation Leo. The planet itself is approximately two and a half times bigger than the Earth and it’s being studied in depth to try and ascertain if atmospheric gases detected could only have come from life. Using the James Webb Space Telescope, researchers detected molecules in K2-18b's atmosphere that are associated with life on Earth, such as dimethyl sulphide (DMS), which is primarily produced by marine algae.
This discovery has led to speculation that K2-18b could be an ocean world teeming with microbial and algal life. Scientists have developed several sophisticated methods to detect atmospheric gases on exoplanets, even those located light-years away. These techniques primarily rely on analysing the light from the host star as it interacts with the planet's atmosphere.
Analysing this filtered light, scientists can identify the specific wavelengths of light that are absorbed by different gases in the atmosphere. However, the excitement surrounding these findings is tempered by caution. The detection of DMS was reported with 0.
3% chance of it being due to random chance. This falls short of the standard required for scientific discoveries, which translates to a 0.00003% chance of a statistical fluke.
Despite these caveats, the potential for life on K2-18b remains a tantalizing prospect. Alfred Russel Wallace, a contemporary of Charles Darwin, co-discovered the theory of evolution and also speculated about the possibility of life elsewhere in the universe. Wallace argued that the conditions necessary for life were likely to be found on other planets, given the vastness of the cosmos.
His work laid the groundwork for modern astrobiology, a field that studies the potential for life beyond Earth, encouraging scientists to consider the possibility of alien life forms. The search for life beyond Earth has a rich history, with Mars often at the centre of speculation. In the late 19th and early 20th centuries, astronomers like Percival Lowell popularized the idea of Martian canals, suggesting that intelligent beings might have constructed them to transport water across the planet's arid surface.
Although later observations debunked the existence of these canals, the notion of life on Mars persisted. When Lowell suggested that there was intelligent life on Mars, Wallace wrote his own book entitled ‘Is Mars Habitable?’ to counter the claims of Lowell. In his book, Wallace thoroughly examined Lowell's claims, arguing that the observed "canals" are likely optical illusions caused by the Earth's atmosphere and the limitations of telescopes at the time.
Wallace concluded that Mars is not only uninhabited by intelligent life but also lacked the conditions to support even simpler life forms. He suggested that the planet's thin atmosphere, low gravity, and a lack of water render Mars uninhabitable. More recently however, the discovery of water deposits holds out some hope for simple lifeforms.
Wallace's book was one of the first works in astrobiology. One of the most compelling pieces of evidence for possible life on Mars came from a Martian meteorite, discovered in Antarctica in 1984. It was the first meteorite discovered in the Alice Hills region in 1984 hence it’s designation as ALH84001.
The meteorite contains structures that some scientists interpreted as fossilized bacteria. In 1996, a team led by NASA's David McKay published a paper suggesting that these structures could be remnants of ancient Martian life. While the claim remains controversial, ALH84001 continues to be a subject of intense study and debate.
H.G. Wells' "The War of the Worlds," published in 1898, is one of the earliest and most famous works of science fiction.
Wells' portrayal of Martians as technologically superior beings likely drew inspiration from contemporary astronomical theories, including Lowell's canals. They were defeated in the end by earthly bacteria and viruses. Beyond Mars, the moons of Jupiter and Saturn have also been considered as potential habitats for life.
Europa, one of Jupiter's moons, has a subsurface ocean beneath its icy crust, making it a prime candidate for microbial life. Similarly, Saturn's moon Enceladus has geysers that spew water and organic molecules into space, suggesting the presence of a subsurface ocean that could harbour life. While no Star Trek character ever said ‘it’s life Jim,’ and Kirk never said ‘beam me up Scotty’, we can still hold out hope of finding life elsewhere in the universe.
Dr James Williams is a reader in science education and communication at Sussex University.
