Curiosity Rover has found new organic molecules on Mars. These aren’t the first organic molecules found on the Red Planet, but they are new on the lengthening timeline of robotic surrogates for humanity there.
Why does this matter? An “organic” molecule is a molecule that contains carbon-hydrogen bonds. All earthly life depends on carbon-hydrogen bonds. The reverse is not true. Not all organic compounds are parts of organisms. So that no amount of organic chemistry by itself establishes the presence of “life on Mars,” that huge-font headline that will make of exobiology a real science.
Still, think of this in Bayesian probability terms. Suppose you had yesterday some reasonable guesstimate as to how likely it is that the planet Mars does or has ever harbored recognizable life. Today you learn a new fact. You learn for the first time that Mars has organic molecules.
It is pretty clear that your guesstimate of that probability will have to increase from its prior.
Strange New Worlds:
Further, with every step in your knowledge of the breadth and complexity of organic chemistry on Mars, reasonable guesstimates again go up. The skeptical priors are left behind on the low side.