And we probably won’t know if it was water, CO2 or dust flow for decades, if not centuries, because what you need on the ground to determine that sort of thing for certain is humans on the surface with instruments, not skateboards with Canons nailed to them or orbiting cameras shooting from a couple of hundred fucking miles away:
Nasa says it has found “compelling” evidence that liquid water flowed recently on the surface of Mars.
The finding adds further weight to the idea that Mars might harbour the right conditions for life.
The appearance of gullies, revealed in orbital images from a Nasa probe, suggests that water could have flowed on the surface in the last few years.
But some scientists think these fresh gullies could also have been cut by liquid carbon dioxide. (Also), further study was needed to determine whether the deposits could have been left there by the flow of dust rather than water…