I have hypothesized in my works that extreme changes in conditions on Mars' surface are correlated
with extreme changes in conditions on Earth's surface - as Earth's surface is becoming sterile
with extinctions, Mars' surface should be increasing habitability, at least partially.
Some evidence for this exists, but new and very strong evidence have recently been revealed.
Water has been
detected
within the top meter of soil in the area of Valles Marineris on Mars.
Under current conditions in Martian atmosphere at the equator (pressure/temperature) water there
cannot be stable - it has to evaporate. Therefore, its presence suggests that, either it is being
replenished or it has been delivered there recently [from the deep].
Of course, if you believe in uniformitarianism (absolute uniformity of nature, constant rates of
geological events), you'll believe in another option - the water is ancient, but it is kept stable
by some unknown special mechanism. While that option cannot be absolutely ruled out, it is the
least probable.
The water might be replenished constantly, but it doesn't make sense that this process started
long time ago - it would imply that Mars is constantly loosing water [to space].
Why would the water that previously existed in atmosphere be compressed and stored into
crust, only to be slowly released into space?
From the perspective of life, that makes sense only if water is going to be replenished
again (ie. with cometary bombardment) or if Mars is dead. While cometary bombardment
of Mars certainly cannot be ruled out, everything suggests that Mars ain't dead (only the surface
is currently devoid of complex life).
Most likely, this water is young and it is part of terraforming of Martian surface, synchronized
with marsforming of Earth's surface.