Water May Have Flowed Intermittently in Martian Valleys for Hundreds of Millions of Years

Category: Cover Story

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Using impact craters as a dating tool, Planetary Science Institute Research Scientist Alexander Morgan has determined maximum timescales for the formation of Martian valley networks shaped by running water.

“Mars today is a global desert, but its surface preserves extensive evidence of past flowing water, including what appear to be river valleys. The timescale over which these valleys formed has big implications for early Mars’ habitability, as long eras with stable liquid water would be more conducive to life,” said Morgan, sole author of “New maximum constraints on the era of Martian valley network formation” that appears in Earth and Planetary Science Letters.

Martian valley networks formed more than 3 billion years ago and have long been considered among the strongest pieces of evidence of liquid water on early Mars. Previous work has found that it took a minimum of tens of thousands of years to erode these valleys, but the frequency of flow events, and thus the total time era over which the valleys formed, has not been constrained.

“In this study, I used craters that predate and postdate valley systems to place maximum bounds of hundreds of millions of years on the era over which these systems formed. Previous work had only determined minimum timescales, so these new results provide an upper bound on the timescale over which Martian valleys were active,” Morgan said. “Given what we know about erosion rates on early Mars, longer timescales imply that conditions permitting rivers were highly intermittent, with long arid periods interspersed with brief episodes of fluvial activity.”

Scientists studying early Mars have historically tended to fall in one of two camps: early Mars was either “warm and wet” with an ocean, or it was “cold and icy” with massive ice sheets.

“Over the past decade or so we’ve come to realize that these descriptors are far too general, and it doesn’t really make sense to try to condense hundreds of millions of years of climate history into a two-word description,” Morgan said. “Like Earth, early Mars was complex, and the conditions permitting surface water likely varied considerably. Earth has undergone massive climatic changes throughout its history – for example, 20,000 years ago the area that is now Chicago was beneath half a mile of ice – and surface conditions permitting rivers on early Mars likewise probably waxed and waned.”