A quote from the article says:

"Modern Mars is cold, desolate, and dry. Its atmosphere contains a mere 0.03% of water vapor. Water can't survive as a liquid. "

The laws of physics dictate that liquid water can exist on Mars for certain lengths of time; consider what the author of the Physics Today article did not:

"Metastability of Liquid Water on Mars" Icarus, Volume 156, Issue 2, pp. 373-386 (2002). Hecht, Michael H.

Abstract:

A simple model of local heat transport on Mars demonstrates that transient melting of ice may occur in depressions and gullies nearly anywhere on the planet where thin ice is illuminated by normal-incidence insolation. An experiment has been performed to confirm the model of evaporation rate at low pressure. Reduction of radiative cooling due to gully geometry is shown to be important. Since appropriate meteorological, topographic, and optical conditions may occur on slopes nearly anywhere on the planet, hydrological features such as gullies would likely form only where such ice might accumulate, notably in sheltered locations at high latitudes. It is suggested that cold-trapping of winter condensation could concentrate a sufficient amount of ice to allow seasonal melting in gullies.

OR:

"The Stability of Liquid-Water Films on the Surface of Mars" American Astronomical Society, DPS meeting #32, #62.08 Quinn, R. C.; Zent, A. P.; McKay, C. P.; Haberle, R. M.

Abstract:

Viking Lander images revealed the existence of water ice (frost) on the Martian surface for extended periods of time during the Martian winter at the VL2 landing site. At the VL2 landing site, and most other locations on Mars, it is expected that water-frost films would completely sublime before liquefaction could occur. While this maybe true for liquefaction of the bulk ice, this process does not necessarily preclude the formation of thin liquid water films at the ice-soil interface in all cases. The formation of such films, even if transient, could play a major role in chemical evolution and weathering on Mars. We present experimentally determined conductance measurements of sublimative loss rates for water ice under Mars-like conditions in the temperature and pressure regimes where thin liquid films exist at the ice-soil interface. A general circulation model is then used to determine the duration and locations where these liquid water films can exist on Mars.

ALSO READ:

"Use of spacecraft data to derive regions on Mars where liquid water would be stable" Proc. Natl. Acad. Sci. USA, Vol. 98, Issue 5, 2132-2137, February 27, 2001 authors Brad Lobitz, Byron L. Wood, Maurice M. Averner, and Christopher P. McKay:

abstract:

Combining Viking pressure and temperature data with Mars Orbital Laser Altimeter topography data, we have computed the fraction of the martian year during which pressure and temperature allow for liquid water to be stable on the martian surface. We find that liquid water would be stable within the Hellas and Argyre basin and over the northern lowlands equatorward of about 40°. The location with the maximum period of stable conditions for liquid water is in the southeastern portion of Utopia Planitia, where 34% of the year liquid water would be stable if it were present. Locations of stability appear to correlate with the distribution of valley networks.