Are aliens hiding in plain sight?
I have had a thread or two about the three new missions to Mars that are, for the first time, looking for life or past life on Mars. But would we recognize it if we found it?
Read the rest at the link.
In July, three unmanned missions blasted off to Mars – from China (Tianwen-1), the US (Nasa’s Mars 2020 Perseverance Rover) and the United Arab Emirates (Hope). The Chinese and American missions have lander craft that will seek signs of current or past life on Mars. Nasa is also planning to send its Europa Clipper probe to survey Jupiter’s moon Europa, and the robotic lander Dragonfly to Saturn’s moon Titan. Both moons are widely thought to be promising hunting grounds for life in our solar system – as are the underground oceans of Saturn’s icy moon Enceladus.
Meanwhile, we can now glimpse the chemical makeup of atmospheres of planets that orbit other stars (exoplanets), of which more than 4,000 are now known. Some hope these studies might disclose possible signatures of life.
But can any of these searches do their job properly unless we have a clear idea of what “life” is? Nasa’s unofficial working definition is “a self-sustaining chemical system capable of Darwinian evolution”. “Nasa needs a definition of life so it knows how to build detectors and what kinds of instruments to use on its missions,” says zoologist Arik Kershenbaum of the University of Cambridge. But not everyone thinks it is using the right one.
Astrobiologist Lynn Rothschild of Nasa’s Ames research centre in California sees a cautionary tale in AA Milne’s story from Winnie-the-Pooh, in which Pooh and Piglet hunt a Woozle without knowing what it looks like and mistake their own footprints for its tracks. “You can’t hunt for something if you have no idea what it is,” she says.
The problem of defining life has haunted planetary scientists ever since Nasa’s two Viking landers touched down on Mars in 1976. Since then, rovers have travelled dozens of miles over the Martian plains but found no hint of life. Would we know it if we saw it, though?
Some astrobiologists – scientists who study the possibility of life on other worlds – think our view is too parochial. We only know of one kind of life: the terrestrial sort. All living things on Earth are made from cells adapted to a watery environment, using molecular machinery built from proteins and encoded as genes in DNA. Few scientists think that extraterrestrial life – if it exists at all – would rely on the same chemicals. “It would be wrong to assume that our familiar biochemistry is what we’re going to find on other planets,” says Kershenbaum. Titan’s surface, for example, is too cold (minus 179C) for liquid water, but the Huygens lander mission of 2005 revealed lakes of another kind, made from hydrocarbons like those in petrol, mainly methane and ethane.