10 Ancient and Recent Lakes on Mars

Abstract

The search for life on Mars is guided by our knowledge of the environments occupied by terrestrial biota. Geology and atmospheric models converge to show that Mars habitability potential was higher during the first 500 Ma of its history. Rivers and lakes, possibly an ocean, started to decline around 3.5 Ga. There is evidence that they may have occurred again in later geological periods but episodically and as lower magnitude events, their formation possibly driven by magmatic pulses and/or obliquity changes. This chapter focuses on Martian lakes and their environmental conditions through time. Paleolakes on Mars were identified first at Viking resolution in basins, impact craters, and volcanic regions. The Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) and Mars Orbiter Laser Altimeter (MOLA) provided additional geological evidence to support the existence of past lakes and showed that the magnitude of the Martian lacustrine activity was much greater than unraveled by Viking. These new data allow the precise definition of watersheds, paleochannel courses and basins and show that lakes abounded on early Mars. Later in the planet’s history, environmental conditions likely included: episodic water supply; increasing evaporation due to the thinning of the atmosphere leading to chemical, pH, and salinity changes in the lakes; high-UV radiation; cool temperatures with seasonal, then perennial icecover; and short to long-term hydrothermal activity for impact and volcanic crater lakes. Evidence for recent water activity through gullies and glaciers opens the possibility for modern short-term ponds as well. Understanding how these conditions could have affected putative life is of paramount importance to assess adaptation and survival potential on a changing Mars.