Present-day Mars could yet harbor life -- but it’s a salty tale. And that tale could resolve the question of common versus independent sources for life at Earth and Mars, and lead to the import of Martians to Earth -- a reverse "contamination."

It appears likely that liquid water on Mars is in the form of highly-concentrated brine -- a saturated salt solution.

That’s good news for a "salt-loving" type of bacteria, the halophile, said Geoffrey Landis, a space scientist at the NASA Glenn Research Center in Cleveland, Ohio. Halobacteria, a form of extremophile archaeobacteria, he said, are adapted to surviving in saturated salt solutions.

Landis said that, at certain spots on Mars, the atmospheric pressure is high enough where water has a liquid phase between ice and vapor. Also, at many locations on the planet, the surface is exposed to above freezing temperatures, making it quite possible that liquid water can briefly persist, he said.

All this adds up, Landis said, to the prospect that liquid water might exist for brief periods during the day, at least at selected surface locations on the Red Planet.

Halobacteria on Mars could live in the concentrated brine, busy metabolizing and reproducing when the brine is in a liquid state. During periods between the liquid state and when the pool is dry, the halobacteria survives in dormant form.

If Mars is not mothering present-day life, one possibility is that this ancient bacteria is preserved in salt deposits on the planet, Landis said.

"Such retrieval of ancient life from Mars would answer many questions about the origin of life, and the relationship or independence of Mars and Earth biology," Landis recently reported in the new journal, Astrobiology.

Furthermore, like Chris McKay of NASA, Landis said that these Martian old-timers could be retrieved, then cultivated in a suitable medium for growth back here on Earth.

The continued assault on Mars with robotic spacecraft is on track for numbers of years hence. Whether the collective data from these probes will coax living proof out of the seemingly dead old world remains to be seen.