On Exoplanet K2-18b Scientists detect signature of life
Science News, but skepticism clouds global story.
Hello Everyone,
There are times where I really want to write about science news on this channel. While I’m obsessed with emerging tech, the exoplanet aspect of astronomy is seriously fascinating for our civilization’s progress.
Recently K2-18b, located 124 light-years from Earth, could be a Hycean world: a potentially habitable planet entirely covered in liquid water with a hydrogen-rich atmosphere, said lead study author , professor of astrophysics and exoplanetary science at the University of Cambridge’s Institute of Astronomy.
Using the James Webb Space Telescope, the team detected chemical fingerprints within the atmosphere of K2-18b that suggest the presence of dimethyl sulfide or DMS, and potentially dimethyl disulfide or DMDS. On Earth, both molecules are only produced by microbial life, typically marine phytoplankton.
This story is one of the biggest moments in exoplanet cosmology or astrobiology. K2-18b had always been a place we’d turn our most powerful future telescopes on and the JWST has not disappointed.
The K2-18b Dilemma
The technique used called transmission spectroscopy, allows scientists to puzzle out the contents of a planet’s atmosphere by seeing how light gets absorbed by its gases on the way toward us. It’s fascinating too since the announcement has been met with floods of scepticism from other researchers who study such ‘biosignatures’ in exoplanet atmospheres.
“It is not strong evidence,” says Stephen Schmidt, an astronomer at Johns Hopkins University in Baltimore, Maryland. “It’s almost certainly not life,” says Tessa Fisher, an astrobiologist at the University of Arizona in Tucson.
It appears also to be somewhat speculative in that Madhusudhan and his colleagues first theorized the concept of Hycean worlds in 2021 after determining there may be liquid water oceans on K2-18b.
Cambridge University Video
Finding evidence of life in the cosmos is the “holy grail” of exoplanet science, one of the scientists said, but there is still a 0.3% chance that the observation is a statistical fluke.
The findings are "the strongest evidence yet that life may exist on a planet outside our solar system," Cambridge University said in a press statement Thursday.
To reach the accepted classification for scientific discovery, the observations would have to cross the five-sigma threshold, meaning there would be below a 0.00006% probability they occurred by chance.
Yet the JWST last September alone, detected carbon dioxide on Jupiter’s icy moon Europa that appears to come from its potentially life-friendly concealed ocean and, possibly, dimethyl sulphide on exoplanet K2-18b, a chemical produced on Earth only by living things.
Sara Seager, an astrobiologist at the Massachusetts Institute of Technology, urges caution for good reason: when it comes to evidence for extraterrestrial life, the remote detection of molecules tends to be inconclusive. Still I think most humans naturally find this fairly exciting.
The planet under discussion is called K2-18b, and it's what's termed a sub-Neptune. It has a radius of about 2.5 times that of Earth's and is 8.6 times more massive. Its orbit is also within the inner edge of its star's habitable range, meaning it receives enough radiation from its star that water could be liquid on its surface, depending on other factors like its atmosphere's composition.
"Concluding that DMS has been detected appears to be premature," Manasvi Lingam, an astrobiologist at the Florida Institute of Technology, who wasn’t involved in the new research.
When a planet wanders across the face of its star, JWST can detect subtle shifts in the light it gathers, caused by compounds in the atmosphere absorbing starlight. Make enough observations and the measurements can confirm which compounds are abundant in the alien air.
How close are we to finding alien life?
I really enjoyed this Op-ed from BigThink in case you are interested in this topic: People are explorers, map makers and essentially curious creatures. At this extends to space, our urge for expansion might have to do with the connectivity of all life.
It’s possible that the molecules were produced by another unknown chemical process on the planet which does not require life. We have yet to find a great example of an “Earth-Twin” even among the thousands of exoplanets that we have identified.
Madhusudhan and his colleagues are building on their research from 2023, in which they detected carbon-based molecules in the atmosphere of K2-18b using the James Webb Telescope's mid-infrared instrument.
Christopher Glein, a planetary scientist at the Southwest Research Institute in Texas who was not involved with the new study, said his reaction to the announcement "is one of interest but restraint."
"I think this is one of those situations where extraordinary claims require extraordinary evidence," says Laura Kreidberg, an astronomer at the Max Planck Institute for Astronomy in Germany who was not part of the research team. "I'm not sure we're at the extraordinary evidence level yet." So the variety of more cautious scientists on this topic is pretty astounding. Astrobiologists have long had these molecules on their “Most Wanted” lists after all and this is not conclusive evidence.
After all, K2-18b is two-and-a-half times the size of Earth and is 700 trillion miles, or 124 light years, away from us.
I get it you know, Prof Madhusudhan said he was surprised by how much gas was apparently detected during a single observation window. Some outlets have gone into great detail of why we should be skeptical.
Scientists are also at a very early stage in understanding the chemistry of sub-Neptune exoplanets like K2-18b. It may be too close to its start to have liquid water in the first place. 38 parsecs from Earth is a long way. The claims of the Cambridge team also seem exaggerated:
Ocean Worlds Teeming with Life
“The only scenario that currently explains all the data obtained so far from JWST, including the past and present observations, is one where K2-18 b is a hycean world teeming with life,” Madhusudhan said.
I get the excitement, huge water worlds could be a thing. “The sub-Neptune frontier has opened a new window into the rich diversity of planetary environments beyond the solar system. The possibility of hycean worlds, with planet-wide oceans and H2-rich atmospheres, significantly expands and accelerates the search for habitable environments elsewhere.” It would also explain why many UFOs seem to be so good at navigating ocean environments. Rightfully in recent years USOs, that is, unidentified objects submerged in water are the best kept secret about alien activity on Earth.
Hycean worlds
Since its discovery in 2015 by the Kepler spacecraft, K2-18 b has become famous as the poster child for a hypothetical category of planets called “Hycean” worlds.
In terms of where we are with exoplanets, 5,800 planets that have so far been identified throughout the Universe. With AI and better telescopes obviously this number will reach tens of thousands in the decades ahead. We’ll get our confirmation of life on other planets sooner rather than later. But Science is a field of global consensus and empirical proof and these things take time.
Matt Genge, a planetary scientist at the Imperial College London, who was not part of the new research, noted that more context and possible formation pathways are needed to explain the abundance of detected molecules in the planet's atmosphere before scientists can confidently attribute the signal to life rather than non-living chemistry or geology. That statements scientists are making to the media also seem rather obvious:
Dr Subir Sarkar, a lecturer in astrophysics at Cardiff University and part of the research team, said the research suggests K2-18b could have an ocean which could be potentially full of life - though he cautioned scientists "don't know for sure".
Finding more exoplanets in their habitable zone is fair enough, but life could also exist outsides of these zones as well. Some scientists propose that K2-18b might not have a water ocean but could be a mini-Neptune or have a molten surface. These hypotheses arise from the varying interpretations of data influenced by factors such as atmospheric conditions and potential geological activity.
Both dimethyl sulfide and dimethyl disulfide, which are part of the same chemical group, have overlapping characteristics, which is why the results can’t definitively differentiate between the two molecules, but future observations might, the study authors said.
Måns Holmberg, a researcher at the Space Telescope Science Institute who was part of the group announcing the findings, said the data they used would be publicly available within days, and he urged other astronomers to independently analyze it. It’s possible K2-18b isn’t an ocean world.
However the researchers behind the new work favor what's called a hycean planet, a merger of hydrogen and ocean. That's because the initial characterization of its atmosphere suggested that, in addition to copious amounts of hydrogen, it had methane and carbon dioxide present but seemingly lacked ammonia and carbon monoxide. The presence of an ocean can account for those chemical properties.
K2-18b
The planet orbits a red dwarf star named K2-18b every 33 days. It has a radius about 2.6 times larger than Earth and a mass approximately 8.6 times that of Earth, which places it between the size of Earth and Neptune. K2-18b orbits a cool dwarf star that lies about 124 light years away, in the constellation of Leo.
In June 2020, NASA scientists reported that it is likely that exoplanets with oceans may be common in the Milky Way galaxy, based on mathematical modeling studies.
Scientists have argued for years about whether Hycean worlds actually exist, and K2-18 b has been at the center of that debate. There are lots of "ifs" and "buts" at this stage, as Prof Madhusudhan's team freely admits.
These latest results are only three sigma, or 99.7%. Certainly the Cambridge team jumped the gun here, but it’s still intriguing to think about.
Since the 1990s we’ve only confirmed roughly 6,000 exoplanets, but as this number accelerates more rapidly with better technology and AI, we’ll have a clearer picture of planetary science. That will open up new possibilities for our curiosity to take hold in new ways that expands the frontiers of our relationship with physical space, space-time and its quantum properties. While astronomy is in a golden age, our quantum capabilities are becoming more intertwined with our space-technologies. Quantum science is still in its infancy with limited funding and a relatively small PhD level talent pool of physicists and engineers.
Nicholas Wogan at the NASA Ames Research Center in California says the evidence is more convincing than the 2023 results, but it still needs to be verified by other groups. Once the data is made public next week, other researchers can start to confirm the findings, but this could take weeks or months due to the difficulty of interpreting JWST data.
The Quantum Foundry is a newsletter primarily interested in startups, venture capital trends and the evolution of pure-play Quantum computing firms. It is however in the news category (see in the app) of Substack, and therefore a kind of science news publication and science stories that directly or indirectly related may sometimes be covered.
