Biosignatures — evidence that says or suggests that life has once been present — are often very hard to find and interpret.
Scientists examining fossilized life on Earth can generally reach some sort of agreement about what is before them, but what about the soft-bodied or even single-celled organisms that were the sum total of life on Earth for much of the planet’s history as a living domain? Scientific disagreements abound.
Now think of trying to determine whether a particular outline on an ancient Martian rock, or a geochemical or surface anomaly on that rock, is a sign of life. Or perhaps an unexpected abundance of a particular compound in one of the water vapor plumes coming out of the moons Europa or Enceladus. Or a peculiar chemical imbalance in the atmosphere of a distant exoplanet as measured in the spectral signature collected via telescope.
These are long-standing issues and challenges, but they have taken on a greater urgency of late as NASA missions (and those of other space agencies around the world) are being designed to actively look for signs of extraterrestrial life — most likely very simple life — past or present.
And that combination of increased urgency and great difficulty has given rise to at least one new way of thinking about those potential signs of life. Scientists call them “agnostic biosignatures” and they do not presuppose any particular biochemistry.
“The more we explore the solar system and distant exoplanets, the more we find worlds that are really foreign,” said Sarah Stewart Johnson, at an assistant professor at Georgetown University and principal investigator of the newly-formed Laboratory for Agnostic Biosignatures (LAB). The LAB team won a five-year, $7 million grant last year from NASA’s Astrobiology Program.
“So our goal is to go beyond our current understandings and find ways to explore the world of life as we don’t know it,” she told me. “That might mean thinking about a spectrum of how ‘alive’ something might be… And we’re embracing uncertainty, looking as much for biohints as biosignatures.”… Read more