Evidence that a comet carrying a European spacecraft is home to an abundance of microbial life "is flimsy at best," according to The Guardian.
Astrobiologist Chandra Wickramasinghe said the comet, named 67P/Churyumov-Gerasimenko, had an organic-rich black crust that was most likely explained by organisms living beneath the icy surface, reported The Guardian on Monday.
But The Guardian later reported that the vast majority of experts agreed that there's no evidence of any life on the comet.
“No scientist active in any of the Rosetta instrument science teams assumes the presence of living micro-organisms beneath the cometary surface crust," Uwe Meierhenrich, an analytical chemist at the University of Nice Sophia Antipolis in France, told The Guardian.
“Scientists are rightly fascinated by the search for life elsewhere, and the possibility of the delivery of life to Earth from elsewhere remains an intriguing line of enquiry. However all measurements from Rosetta or by Earth-based telescopes on comets can be explained by much simpler chemical and physical processes than involving extra-terrestrial life," said Professor Alan Fitzsimmons of Queens University, according to the Christian Science Monitor.
“These scientists seem to have forgotten Carl Sagan’s maxim that ‘extraordinary claims require extraordinary evidence’. They don’t have it.”
The European Space Agency landed the Philae spacecraft on the comet in November, and the lander awoke from hibernation last month after recharging its solar panels as the comet approaches the sun.
Meierhenrich disputed claims that neither Philae or Rosetta, a spacecraft orbiting the comet, are equipped to search for direct evidence of life.
"I wanted to include a very inexpensive life-detection experiment, (but) at the time it was thought this was a bizarre proposition,” Wickramasinghe had said.
Meierhenrich, however, said data obtained by the Philae probe could be used to distinguish between biological and non-biological matter on the comet.
The comet’s black hydrocarbon crust overlays smooth icy areas and craters filled with re-frozen water and organic debris -- and Wickramasinghe said evidence suggests that micro-organisms may have helped form the icy structures and the numerous aromatic hydrocarbons detected by scientists.
“These are not easily explained in terms of prebiotic chemistry,” Wickramasinghe said. “The dark material is being constantly replenished as it is boiled off by heat from the sun, (and) something must be doing that at a fairly prolific rate.”
Rosetta has picked up strange “clusters” of organic materials that resemble viral particles, the researcher said, and computer simulations have suggested microbes may inhabit its watery areas.
Wickramasinghe and a colleague believe the comet and others could provide homes to microbes like the “extremophiles” that live in the Earth’s most inhospitable regions.
He believes that comets may have helped sow the seeds of life on Earth and other planets, and the astronomer also has suggested that the SARS virus may have arrived from space.
“Five hundred years ago it was a struggle to have people accept that the Earth was not the center of the universe,” Wickramasinghe said. “After that revolution our thinking has remained Earth-centered in relation to life and biology. It’s deeply ingrained in our scientific culture and it will take a lot of evidence to kick it over.”
But The Guardian noted that "Wickramasinghe has a history of claiming to have detected extraterrestrial microbes" and his work has been rejected by mainstream scientists.
(Note: This story was updated to include information casting serious doubt on Chandra Wickramasinghe's claims.)