Life on K2-18b increasingly unlikely
Recently, researchers allegedly found signs of life on an exoplanet. New research data now makes this seem very unlikely.
(Image: A. Smith / N. Mandhusudhan)
The probability of life on the exoplanet K2-18b, which was discovered in 2015 with the help of the Kepler space telescope, has fallen sharply due to new research findings. In April, a research team led by Nikku Madhusudhan at the University of Cambridge wrote that they had found the “clearest traces of extraterrestrial life to date” on the exoplanet at a distance of 124 light years.
This was prompted by signatures of the biomarkers DMS and DMDS in the spectrum of the exoplanet's atmosphere recorded by the James Webb Space Telescope (JWST). Various research groups have already expressed doubts about this statement, for example because the signal is not clear enough, DMS and DMDS are not reliable biomarkers, or other models could also explain the signatures in the spectrum.
New research results from a team led by Renyu Hu from the California Institute of Technology (Caltech) now indicate that there is no statistical evidence for biomarkers in the atmosphere. The manuscript has not yet been reviewed by independent experts. The study is based on data from the near-infrared sensor NIRSpec of the JWST – a different sensor than was used for the results from April.
Lifeless water world K2-18b?
To explain the measured spectrum, the researchers tried out various models and compared them with the experimental data. They detected methane and carbon dioxide and provided further evidence that there must be plenty of water on K2-18b, either in the atmosphere or in an ocean.
However, models that assumed the existence of DMS and DMDS in the atmosphere did not necessarily provide better agreement with the data. The claim about extraterrestrial life on K2-18b is therefore not supported, at least based on the current data, the authors write.
“This model dependence suggests that it is a very weak signal, if there is a signal at all,” Hu tells New Scientist. Madhusudhan agrees that there is not enough data for clear evidence. However, he still considers biomarkers to be the most likely explanation for the observed signal.
(olb)
