This artist’s concept shows what exoplanet K2-18 b could look like based on new observation. The exoplanet, of a size between Earth and Neptune, orbits the cool dwarf star K2-18. A new investigation of the planet with the James Webb Space Telescope has revealed the presence of carbon-bearing molecules in the atmosphere, including methane and carbon dioxide. (NASA, CSA, ESA, J. Olmsted (STScI), Science: N. Madhusudhan (Cambridge University)
Beware easy answers to the question of whether life exists beyond Earth.
Be they “alien” skeletons in Mexico City, interstellar probes that briefly pass through our solar system, UFOs of all sorts and claims to have found “biosignature” chemical byproducts of life around planets where many other factors say that life cannot exist — their chances of being meaningful are vanishingly small.
But they make good copy, can bring quick attention and even fame to researchers and sidekicks, and they often cannot be proven 100 percent wrong. Data from planets close and distant, solar systems like ours and stunningly different and faraway galaxies we have only begun to understand are often way too complex to completely dismiss possibilities.
Unless, of course, they can be shown to be entirely different than claimed, as were the two “non-human corpses” put on display this month in Mexico City by a well-known ufologist and debunked as a mash-up of human and animal bones or ancient mummies from Peru.
The real recent astrobiology news came instead from new results featuring the James Webb Space Telescope and its reading of the atmosphere of a large planet (8.6 times more massive than Earth) 120 light-years away. Researchers found methane and carbon dioxide in its atmosphere and possibly a hydrogen-rich atmosphere that surrounds an ocean-covered surface.
The findings, by a team at the University of Cambridge, do not claim to have detected signs of life, although they also reported the possible presence of a molecule called dimethyl sulfide (DMS). On Earth, this is only produced by life, with the bulk of the compound in Earth’s atmosphere coming from phytoplankton in watery environments.
But instead of focusing on a single molecule, Nikku Madhusudhan, an astronomer at the University of Cambridge and lead author of the paper, point elsewhere to the importance of their work — that the planet is large and not necessarily rocky yet it has that interesting suite of chemicals in its atmosphere.
“Our findings,” he said in a release, “underscore the importance of considering diverse habitable environments in the search for life elsewhere.”
“Traditionally, the search for life on exoplanets has focused primarily on smaller rocky planets, but the larger (watery) worlds are significantly more conducive to atmospheric observations.”
The graphic shows Webb’s spectra of the exoplanet K2-18 b. Magenta, red and green vertical columns across the plot indicate signatures of methane, carbon dioxide, and dimethyl sulfide. Behind the graph is an illustration of the planet and its star. (NASA, CSA, ESA, R. Crawford (STScI), J. Olmsted (STScI), Science: N. Madhusudhan (Cambridge University)
The new Webb discovery adds to recent studies suggesting that K2-18 b could indeed be a Hycean exoplanet, one which has the potential to possess a hydrogen-rich atmosphere and a surface covered with ocean water. The first insight into the atmospheric properties of this habitable-zone exoplanet came from observations with NASA’s Hubble Space Telescope, which prompted further studies that have since changed our understanding of the system.
The abundance of methane and carbon dioxide in the atmosphere, and a shortage of ammonia, support the hypothesis that there may be a water ocean on the planet surface. Frequently, a particular combination of atmospheric molecules gives researchers much more important information than the presence of a single chemical element.
Exoplanets such as K2-18 b, which have sizes between those of Earth and Neptune, are unlike anything in our solar system. This lack of equivalent nearby planets means that these “sub-Neptunes” or “super-Earths” are poorly understood, and the nature of their atmospheres is a matter of active debate among astronomers.
The suggestion that the sub-Neptune K2-18 b could be a Hycean exoplanet is intriguing, as some astronomers believe that these worlds are promising environments to search for evidence for life on exoplanets.
Still, many addition observations are needed to move the K-12 b finding beyond intriguing to something more substantial, Madhusudhan said, and that will take time and the power of the Webb.
Nikku Madhusudhan is Professor of Astrophysics and Exoplanetary Science at the Institute of Astronomy of the University of Cambridge. (42Evolution)
“Our findings underscore the importance of considering diverse habitable environments in the search for life elsewhere,” Madhusudhan said.
These initial Webb observations also produced the possible detection of a molecule called dimethyl sulfide (DMS). On Earth, this is only produced through biology, with the bulk of the compound in Earth’s atmosphere emitted from phytoplankton in marine environments.
The inferred presence of DMS is less robust than the detections of other molecules in the K2-18b atmosphere , Madhusudhan said, and requires further validation via Webb observations.
While K2-18 b lies in the habitable zone, and is now known to harbor carbon-bearing molecules, this does not necessarily mean that the planet can support life. The planet’s large size — with a radius 2.6 times the radius of Earth — means that the planet’s interior likely contains a large mantle of high-pressure ice, like Neptune, but with a thinner hydrogen-rich atmosphere and an ocean surface.
Hycean worlds are predicted to have oceans of water. However, it is also possible that these oceans are too hot to be habitable or be liquid.
The team’s results were accepted for publication in The Astrophysical Journal Letters.
Artist’s concept of a Hycean planet, with a global ocean and hydrogen atmosphere. (Amanda Smith/ University of Cambridge)
Characterizing the atmospheres of exoplanets such as K2-18 b — meaning identifying their gases and physical conditions — is a very active area in astronomy, and the Webb telescope is producing results that are more robust than expected or even hoped.
The K2-18 planet was discovered in 2015 with NASA’s K2 mission, an extension of the iconic Kepler mission. K2-18 b is a transiting exoplanet, meaning that it creates a detectable drop in brightness as it passes across the face of its host star.
During these transits, a tiny fraction of starlight will pass through the exoplanet’s atmosphere before reaching the Webb, the first space telescope with the power and scope to identify a range of hitherto hidden atmospheric molecules. The starlight’s passage through the exoplanet atmosphere leaves traces that astronomers can piece together to determine the gases of the exoplanet’s atmosphere.
“This result was only possible because of the extended wavelength range and unprecedented sensitivity of Webb, which enabled robust detection of spectral features with just two transits,” said Madhusudhan. “For comparison, one transit observation with Webb provided comparable precision to eight observations with Hubble conducted over a few years and in a relatively narrow wavelength range.”
Contrast this intensive and pain-staking research with some of the other recent claims of having found signs, or the presence, of extraterrestrial life.
The two alien “remains” were presented by a journalist and ufologist Jaime Maussan at a Mexico City Congressional meeting UFOs and aliens. The alleged remains, which reportedly came from Peru, were dismissed by scientists and other experts as possibly mummified bodies or recently constructed fakes from human and animal bones. But they also became a global sensation despite the lack of any serious scientific research into what they are.
Avi Loeb off Papua New Guinea, with objects found on the ocean floor that he claims came from outside our solar system.(Avi Loeb)
Also winning wide attention, and broad skepticism, have been the extraterrestrial claims of Avi Loeb. He’s a Harvard University theoretical physicist known for his cosmology work, but he now has many in the astrobiology field pulling out their hair in frustration.
This summer, Loeb mounted an expedition to the waters off Papua New Guinea to search for pieces of an object — a meteorite from outside our solar system or something else that he describes as possibly “more exotic.” Loeb had searched the records of NASA’s Center for Near Earth Object Studies and had found reports of what appeared to be a particularly fast-moving asteroid that crashed down through our atmosphere and into the ocean in 2014. For a meteorite to be especially fast-moving as it entered the Earth’s atmosphere could mean it came from outside the solar system.
Loeb’s expedition to the site — funded in large part by a cryptocurrency entrepreneur — dredged the ocean bottom with a magnetic sled equipped to pick up pieces of the objecdt. In two weeks, his team came up with scores tiny (sub-millimeter), rounded beads that contained molecules that Loeb later concluded had to have been formed outside our solar system.
He and colleagues in the Galileo Project at Harvard/Smithsonian Center for Astrophysics, a recently-formed group that focuses on potential signs of extraterrestrial technology, have already written a paper about their findings, but it has not been published so far in a journal. Nonetheless, Loeb has gone unusually public with his views regarding the “spherules” and their claimed interstellar origins, and he had his ocean journey filmed and widely distributed.
The issue of what many in the field see as exaggerated and out-of-context astrobiology claims has been growing for some time.
For instance, a group of senior NASA officials and scientists proposed in Nature last year that scientists working in astrobiology begin to include in their papers a formal confidence scale regarding their research into life beyond Earth. The scale they proposed would make it easier for the pubic, and scientists, to know what bars had been cleared, and not cleared, in making the astrobiological case the scientists putting forward.
The logic behind the proposal is that the issue of possible life beyond Earth is so important and so fraught that guardrails are needed — just as they have been implemented in other space science fields, such as near Earth asteroid detection.
The journal paper proposal, and an ensuing community workshop and white paper, have received some pushback, but the need to pay greater attention to astrobiology claims and how they are being shared with the public has been definitely highlighted.
Also of concern is that the public — and that very much includes the taxpaying pubic — could grow weary of bold claims about the discovery of signs of extraterrestrial life when follow-up work finds no such thing. The funds needed to build future space telescopes that could actually bring us closer to scientific evidence of ET life are enormous; claims about aliens and UFOs, as well as thin “discoveries” of biosignatures and interstellar objects, may in time so confuse people that many will lose patience.
Artist’s concept of interstellar object given the name Oumuamua as it passed through the solar system after its discovery in October 2017. The shape and its ability to pick up great speed is unlike that of any object seen in our own solar system. This led to suggestion the object was a space probe but recent journal articles have provided very different scientific explanations. (European Southern Observatory/ M. Kornmesser)
This confidence scale was proposed well before Loeb’s recent spherule claims, but after a similar earlier controversy about an interstellar object that was known to pass through our solar system in 2017. Loeb argued that the small, thin object, which increased its speed significantly at one point, could well be a probe from a faraway civilization and he wrote a book with that view as a theme.
But scientists have dismissed his speculations and papers in Nature and Science this spring both concluded the object was an unusual comet or a watery planetesimal fragment from outside the solar system, and the pick-up in speed was explained as a function of the object’s make-up.
While science of all kinds, and especially space science, has a long history of being modified or even transformed by seemingly radical new theories and findings, astrobiology is all about the very multi-disciplinary hard work of making new discoveries and then working to understand them in the broadest contexts possible.
The recent University of Cambridge detection of methane and carbon dioxide in the atmosphere of a distant exoplanet, as well as the possible detection of the earthly biosignature dimethyl sulfide, are part of that grand astrobiological effort, and the results were reported with rigor, restraint and care.
Most scientists involved in research into potential life beyond Earth work with a similar sense of responsibility. For those who don’t, some guardrails might be useful.
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