Ancient Mars could have been cold and still had flowing liquid water

Presence of Antarctic lakes in spite of freezing temperatures inspired study of early Mars.
By Laurel Kornfeld | Oct 18, 2017
Even if ancient Mars had been cold and icy rather than warm and wet, liquid water could still have flowed on its surface, according to a new study published in the journal Icarus.

While valleys and lakebeds on the Martian surface indicate water once flowed there, scientists continue to debate whether the planet was cold and icy or warm and wet during its ancient days.

Computer models of Mars' early atmosphere suggest its climate was cold and icy.

Based on climate dynamics observed in Antarctica, where temperatures vary seasonally enough to sustain lakes even when mean temperatures are below freezing, three scientists sought to determine whether a similar mechanism could have occurred on ancient Mars.

They hypothesized that liquid water could have formed on Mars during seasonal melting much like it forms in Antarctica, even if the general climate had been icy and cold.

Although the planet could have been completely frozen for most of its year, peak summer temperatures could have melted the edges of glaciers, producing enough liquid water to carve the valleys and lakebeds seen on the planet today.

Other sources of warming, such as volcanoes and impact cratering, could also have melted ice into liquid water.

To test their theory, Ashley Palumbo and Jim Head of Brown University's Department of Earth, Environmental and Planetary Science, and Robin Wordsworth of Harvard University's School of Engineering and Applied Sciences ran state-of-the-art computer climate models for Mars.

The models assumed the composition of ancient Mars' atmosphere to be largely carbon dioxide with small amounts of other greenhouse gases. Mars' atmosphere is known to have been thicker billions of years ago, but how much thicker remains unknown.

To account for this, the researchers ran models with a variety of atmospheric thicknesses and the resulting increases or decreases of greenhouse warming they produced.

The computer models also accounted for the fact that the Sun's output billions of years ago was weaker than it is today--another factor that would account for colder temperatures on Mars.

Other variables were added to the computer models to account for a variety of unknowns regarding early Mars. These included several different axial tilts, which would have altered the amounts of sunlight received by upper and lower latitudes, and various levels of orbital eccentricity, which would have influenced seasonal changes.

Several scenarios in the model showed the area of the valley networks covered with ice and mean temperatures remaining below freezing while at the same time, southern highland summer temperatures warmed above the freezing point.

Palumbo also incorporated data from an earlier study indicating the volume and rate of water runoff needed to have created the valleys and lakebeds.

With that data added, the model that best fit was one in which Mars had an orbit more eccentric than its current one, something entirely plausible in the planet's early history.




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