Leonard David's INSIDE OUTER SPACE

NASA 1976 Viking 2 lander image of the Mars Utopian Plain.
Credit: NASA/JPL-CalTech

The idea that modern Mars is entirely devoid of liquid water is being challenged by data gleaned from the 1970s NASA Viking 2 landing site.

These findings provide “a new perspective on the transient presence of liquid water on Mars, a key factor in assessing planetary habitability.”

That’s the view of Vincent Chevrier, an associate research professor at the University of Arkansas’ Center for Space and Planetary Sciences. His case for the existence of liquid brines on Mars was recently published in Nature Communications Earth and Environment.

Frost factoid

Chevrier’s research combined Viking 2 meteorological data and computer modeling.

Image credit: NASA/JPL-Caltech/E. Vandencbulek

“The confirmation that brines can form at the Viking 2 landing site during late winter — albeit for short periods — suggests that similar processes may occur in other frost-bearing regions, especially at mid-to-high latitudes” on the Red Planet, Chevrier’s paper – “Perchlorate brine formation from frost at the Viking 2 landing site” – states, “which could guide the planning of future astrobiological investigations.”

The new looksee into Viking 2 data could mean the planet might have supported life adapted to a much colder, drier planet.

NASA’s Viking 2 landed on Mars in 1976. “It was the only mission that clearly observed, identified and characterized frost on Mars,” Chevrier says in a University of Arkansas research posting.

However, frost on Mars tends to sublimate rapidly, transitioning from a solid to a gas quickly, without spending much time in a liquid state due to atmospheric conditions on the Red Planet.

Image credit: NASA/JPL-Caltech/AndreaLuck

Brief window

In sifting through the Viking 2 meteorological data, combined with data from the Mars Climate Database, Chevrier found there was a brief window in late winter and early spring when the conditions were right for the formation of brines.

That period of time spans one Mars month — roughly equivalent to two Earth months — where the conditions were generally ideal in the early morning and late afternoon.

“Robotic landers equipped with in situ hygrometers [to gauge moisture content in air] and chemical sensors could target these seasonal windows to directly detect brine formation and constrain the timescales over which these liquids persist,” Chevrier’s research paper notes.

Mosaic of the Valles Marineris hemisphere of Mars composed of 102 Viking Orbiter images of this huge feature on the Red Planet.
Credit: NASA, USGS, Viking Project

Brine stability

The research scientist adds that the methodology applied — using Viking 2 meteorological data to reconstruct brine stability – could be extended to datasets from more recent missions, such as NASA’s InSight lander and the Curiosity rover, to appraise whether similar processes occur in different climatic settings.

“Moreover, this work underscores the need for future landers to deploy high-resolution imaging and thermal mapping to track frost evolution in real-time,” Chevrier concludes.

To access the research paper – “Perchlorate brine formation from frost at the Viking 2 landing site” – go to:

https://www.nature.com/articles/s43247-025-02411-0

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