This is in response to Nick Hoffman's post at http://www.habitablezone.com/space/messages/15609.html

Nick wrote:
As for modern Mars, the concept of liquid water a mere 1 km down is pure pipedream. The heat flow, surface temperature, and the mulling effect of clathrate on brines mean that at the equator one expects liquid water at 7 km.

Alex writes:
A couple of points for the benefit of others who may not follow the peer-reviewed literature closely:

Nick's flat assertion that near-surface liquid H2O on modern day Mars is a "pure pipedream" is certainly an opinionated, if not minority, position. While it is true that the commonly accepted depth to the melting isotherm in the equatorial regions is currently on the order of km's (1-3 km to be precise)

See, for example, http://humbabe.arc.nasa.gov/mgcm/faq/liquid.html

, which implies, due to thermal diffusivity arguments, a desseciated near-surficial environment at these latitudes, one should note, for balance, that the Malin and Edgett seepage gullies (at latitudes polewards of 30 degrees) *are* evidence for near-surface liquid water on Mars today, with *today* being defined in geologic epochs. While many workers (including Nick) have pointed out and/or acknowledged the difficulty in explaining the sequestration of liquid water (presumably in aquifers) in the current cyrogenic Martian environment, one should note a couple of recently published papers that offer *plausible* mechanisms that attempt to reconcile this problem:

Mellon, Michael T. ; Phillips, Roger J. 2001
Recent gullies on Mars and the source of liquid water
J. Geophys. Res. Vol. 106 , No. E10 , p. 23,165 (2000JE001424)

Cryovolcanism and the Recent Flow of Liquid Water on Mars
Eric J. Gaidos
Icarus Vol. 153, No. 1, September 1, 2001, pp. 218-223
Abstract
http://www.idealibrary.com/links/doi/10.1006/icar.2001.6649

Alex R. Blackwell
University of Hawaii