"Life is a self-sustained chemical system capable of undergoing Darwinian evolution."
That's the so-called "NASA definition of life."
Or there's Russian-born geneticist Edward Trifonov's take: Life is "self-reproduction with variations."
Or there's "Life is an expected, collectively self-organized property of catalytic polymers." Or "Life is a metabolic network within a boundary."
It's said that, "There are as many definitions of life as there are people trying to define it." And yet, none of those definitions is quite right.
Science writer Carl Zimmer says that's strange behavior for scientists: "It is as if astronomers kept coming up with new ways to define stars."