Since 2012, NASA's Curiosity rover has explored Gale Crater, a site scientists believe once held a vast lake billions of years ago. The mission's core aim: evaluate Mars' habitability in this ancient watery setting. Yet, emerging evidence suggests we may need to reconsider.
Recently, Curiosity marked nine years on the Red Planet, methodically traversing Gale Crater—widely interpreted as the remnants of a lake from over three billion years ago. Through extensive surveys and high-resolution imagery, the rover has gathered compelling data. Layered sediments in the Murray Formation and central Mount Sharp point to deposition by flowing water carrying sand and silt, bolstering the ancient lake theory.
A new study from the University of Hong Kong's Department of Earth Sciences, published in Science Advances, challenges this narrative. The researchers analyzed rover data and conclude that most sediments were wind-deposited sand and silt, not lakebed accumulations. Water played a role—likely as acid rain—but in far smaller volumes, forming shallower, more transient lakes than previously envisioned.
The analysis focuses on elemental mobility: some elements dissolve readily in water (mobile), while others resist (immobile), influenced by the fluid's chemistry (acidic, saline, oxidizing, etc.).
Immobile elements here correlate strongly and enrich at higher altitudes in rock profiles, indicating downward weathering—not lake-bottom deposition, where they'd concentrate lower. Iron depletion with intensifying weathering further signals a reducing (oxygen-poor) atmosphere, not an oxidizing one.
"Their data challenges existing assumptions about both the depositional environment of these unique rock formations and the atmospheric conditions in which they formed," summarizes Dr. Ryan McKenzie of the university. "Specifically, the authors show evidence of weathering processes under a reducing atmosphere in a subaerial desert-like environment, rather than formation in a watery lacustrine environment."
Pinpointing the history of rocks from tens of millions of kilometers away is inherently challenging. Still, this rigorous study refines our understanding of ancient Mars—and offers parallels for early Earth.
