Mar 20, 2024 05:37 PM
https://www.quantamagazine.org/doubts-gr...-20240319/
EXCERPTS: A slew of recent papers explore the daunting uncertainties in exoplanet biosignature detection. One key challenge they identify is what the philosopher of science Peter Vickers at Durham University calls the problem of unconceived alternatives. Put simply, how can scientists be sure they’ve ruled out every possible nonbiological explanation for the presence of a gas — especially so long as exoplanet geology and chemistry remain nearly as mysterious as alien life?
“New ideas are being explored all the time, and there could be some abiotic mechanism for that phenomenon that just hasn’t been conceived of yet,” Vickers said. “That’s the problem of unconceived alternatives in astrobiology.”
[...] If or when scientists detect a putative biosignature gas on a distant planet, they can use a formula called Bayes’ theorem to calculate the chance of life existing there based on three probabilities. Two have to do with biology.
The first is the probability of life emerging on that planet given everything else that’s known about it. The second is the probability that, if there is life, it would create the biosignature we observe. Both factors carry significant uncertainties, according to the astrobiologists Cole Mathis of Arizona State University and Harrison Smith of the Earth-Life Science Institute of the Tokyo Institute of Technology, who explored this kind of reasoning in a paper last fall.
The third factor is the probability of a lifeless planet producing the observed signal — an equally serious challenge, researchers now realize, that’s tangled up in the problem of unconceived abiotic alternatives.
“That’s the probability that we argue you can’t fill in responsibly,” Vickers said. “It could almost range from anything from zero to 1.”
[...] Unconceived alternatives have already forced astrobiologists multiple times to revise their ideas about what makes a good biosignature....
[...] Today, astrobiologists have largely abandoned the idea that a single gas could be a biosignature. Instead, they focus on identifying “ensembles,” or sets of gases that couldn’t coexist without life....
[...] So far, scientists haven’t managed to come up with an abiotic explanation for oxygen-methane biosignatures. But Vickers, Smith and Mathis doubt that this particular pair — or perhaps any mix of gases — will ever be convincing... (MORE - missing details)
EXCERPTS: A slew of recent papers explore the daunting uncertainties in exoplanet biosignature detection. One key challenge they identify is what the philosopher of science Peter Vickers at Durham University calls the problem of unconceived alternatives. Put simply, how can scientists be sure they’ve ruled out every possible nonbiological explanation for the presence of a gas — especially so long as exoplanet geology and chemistry remain nearly as mysterious as alien life?
“New ideas are being explored all the time, and there could be some abiotic mechanism for that phenomenon that just hasn’t been conceived of yet,” Vickers said. “That’s the problem of unconceived alternatives in astrobiology.”
[...] If or when scientists detect a putative biosignature gas on a distant planet, they can use a formula called Bayes’ theorem to calculate the chance of life existing there based on three probabilities. Two have to do with biology.
The first is the probability of life emerging on that planet given everything else that’s known about it. The second is the probability that, if there is life, it would create the biosignature we observe. Both factors carry significant uncertainties, according to the astrobiologists Cole Mathis of Arizona State University and Harrison Smith of the Earth-Life Science Institute of the Tokyo Institute of Technology, who explored this kind of reasoning in a paper last fall.
The third factor is the probability of a lifeless planet producing the observed signal — an equally serious challenge, researchers now realize, that’s tangled up in the problem of unconceived abiotic alternatives.
“That’s the probability that we argue you can’t fill in responsibly,” Vickers said. “It could almost range from anything from zero to 1.”
[...] Unconceived alternatives have already forced astrobiologists multiple times to revise their ideas about what makes a good biosignature....
[...] Today, astrobiologists have largely abandoned the idea that a single gas could be a biosignature. Instead, they focus on identifying “ensembles,” or sets of gases that couldn’t coexist without life....
[...] So far, scientists haven’t managed to come up with an abiotic explanation for oxygen-methane biosignatures. But Vickers, Smith and Mathis doubt that this particular pair — or perhaps any mix of gases — will ever be convincing... (MORE - missing details)
