  Channel networks on the plateau adjacent to Juventae Chasma have the highest
drainage densities reported on Mars.We model frozen precipitation on the
Juventae plateau,finding that the trigger for forming these channel networks
could have been ephemeral lakeshore precipitation,and that they do not require
past temperatures higher than today.If short-lived and localized events explain
some dendritic channel networks on Mars, this would weaken the link between
dendritic valley networks and surface climate conditions that could sustain
life. Our analysis uses MRAMS simulations and HiRISE DTMs.We model localized
weather systems driven by water vapor release from ephemeral lakes during
outflow channel formation.At Juventae Chasma,mean snowfall reaches a maximum of
0.9mm/hr water equivalent on the SW rim of the chasm.Radiative effects of the
thick cloud cover raise maximum (minimum, mean) plateau surface temperatures by
up to 24K(9K, 17K)locally.The key result is that the area of maximum modeled
precipitation shows a striking correspondence to the mapped Juventae plateau
channel networks.Three independent methods show this fit is unlikely to be due
to chance.We use a snowpack energy balance model to show that if the snow has
the albedo of dust(0.28), and for a solar luminosity of 0.8($\equiv$3.0Gya),
then if the atmospheric greenhouse effect is unchanged from(6K warmer
than)today only 0.4%(21%)of lake-induced precipitation events produce snowpack
that undergoes melting.However, warming from associated dense cloud cover would
allow melting over a wider range of conditions.In these localized precipitation
scenarios, global temperatures need not be higher than today, and the rest of
the planet remains dry.
