Mysterious 'Fingers' on Mars May Point Towards Salt Water Presence

Detailed observations near the equator on Mars, have revealed slender, finger-like markings - possibly due to salt water - that appear to expand down the slopes with the seasons.

The dark markings are typically less than 16 feet wide and appear extending down rocky Martian slopes during spring and summer, but fade during wintertime and return the following spring.

Scientists have observed these markings at a number of sites in the Valles Marineris, one of the largest canyon systems in the solar system. At these sites, the dark markings appear on north-facing canyon slopes, becoming apparent when the slopes receive the most sunshine. The slopes' south-facing counterparts seem to expand when the seasons shifts and more sunshine hits their side.

The best explanation scientists have come up with is that the markings are made by water.

"The equatorial surface region of Mars has been regarded as dry, free of liquid or frozen water, but we may need to rethink that," said Alfred McEwen, a principal investigator in the study of the markings.

"The explanation that fits best is salty water is flowing down the slopes when the temperature rises," McEwen said. "We still don't have any definite identification of water at these sites, but there's nothing that rules it out, either."

Dissolved salts can keep water melted at temperatures lower than than the freezing point of pure water. Salts can also slow the evaporation rate of water, which could explain why these thin dark streaks are so long.

Further study of the dark markings will likely paint a clearer picture of the presence of ice or water on Mars.

"The more we find, the more we can fill in a global map of where ice is buried," said Colin Dundas of the US Geological Survey in Flagstaff, Ariz. "We've now seen icy craters down to 39 degrees north, more than halfway from the pole to the equator. They tell us that either the average climate over several thousand years is wetter than present or that water vapor in the current atmosphere is concentrated near the surface. Ice could have formed under wetter conditions, with remnants from that time persisting today, but slowly disappearing."

Click here to see a GIF animation of the Mars fingers expanding with the seasons. 

The results of this study were presented in San Francisco this week at the 46th Annual Fall Meeting of the American Geophysical Union.