Introduction
Mars is a dry and dusty planet today, but its surface features suggest that it once had abundant liquid water. One of the most striking examples of this ancient water activity are the valley networks, which resemble river systems on Earth. These valleys have been considered as evidence of a warmer and wetter climate on early Mars, and as potential habitats for life. However, the origin and evolution of these valleys remain poorly understood. How long did it take to carve these valleys? How often did water flow on Mars? And what does this imply for the habitability of the red planet?
New Constraints from Crater Dating
A new study by Planetary Science Institute Research Scientist Alexander Morgan has shed some light on these questions by using impact craters as a dating tool. Impact craters are formed when asteroids or comets collide with the surface, and their number and size can be used to estimate the age of a region. Morgan used craters that predate and postdate the valley networks to place maximum bounds on the era over which these systems formed. He found that the valleys could have formed over hundreds of millions of years, much longer than previously thought.
Implications for Mars’ Climate and Habitability
The long timescale of valley formation suggests that water flow on Mars was intermittent, with long dry periods interspersed with brief episodes of fluvial activity. This is consistent with other lines of evidence that indicate that early Mars was not uniformly warm and wet, but rather experienced complex and variable climatic conditions. Morgan also proposed that the erosion rate of the valleys was very slow, similar to parts of the Atacama Desert in Chile. This could be explained by the accumulation of large boulders on the riverbeds, which could not be further broken down by water. Alternatively, it could imply that water flowed very infrequently, perhaps as little as 0.001% of the time.
The new study has important implications for the habitability of early Mars, as it suggests that stable liquid water was rare and transient on the surface. This would make it more challenging for life to originate and persist on the red planet, compared to Earth. However, it does not rule out the possibility of life altogether, as there could have been other sources of water and energy in the subsurface or in impact craters. Future missions to Mars, such as NASA’s Perseverance rover and ESA’s ExoMars rover, will continue to explore the ancient environments and search for signs of past life.