Today's promised mystery announcement
from NASA has finally been made: dotancohen
writes "A NASA orbiter has found possible evidence for water on the surface of Mars that flows seasonally. The water likely would be salty, in keeping with the salty Martian environment."
Adds an anonymous reader: "Dark, finger-like features appear and extend down some Martian slopes
during late spring through summer, fade in winter, and return during the next spring, NASA says, and repeated observations have tracked the seasonal changes in these recurring features on several steep slopes in the middle latitudes of Mars' southern hemisphere."
You can find more on the claimed find at NASA TV