Mars used to be a dramatically different planet before losing its atmosphere. (© IM_VISUALS - stock.adobe.com)
HOUSTON — Four billion years ago, Mars might have looked a lot more like Earth than we thought – not on the surface, where rusty red deserts stretched toward the horizon, but deep underground, where vast bodies of granite may have been forming in much the same way as Earth’s mountain ranges. This fascinating possibility emerges from new research that suggests Mars’ geological history is far more complex and Earth-like than scientists previously believed.
A groundbreaking study published in the journal Earth and Planetary Science Letters reveals that ancient Mars likely harbored massive granite formations beneath its surface, alongside hidden reservoirs of liquid water that could have sustained potential life. The research, led by Cin-Ty Lee of Rice University, challenges our understanding of how granite – the same rock that forms Earth’s majestic peaks like Yosemite’s Half Dome – could have formed on a planet without plate tectonics.
“Our findings indicate that Mars’ crustal processes were far more dynamic than previously thought,” says Lee, who serves as the Harry Carothers Wiess Professor of Geology at Rice University, in a media release. “Not only could thick crust in the southern highlands have generated granitic magmas without plate tectonics, but it also created the thermal conditions for stable groundwater aquifers — reservoirs of liquid water — on a planet we’ve often considered dry and frozen.”
The key to this discovery lies in Mars’ unusually thick crust, particularly in its southern highlands, which reaches up to 80 kilometers thick (roughly 50 miles) – far exceeding Earth’s continental crust. Using sophisticated thermal modeling, the research team demonstrated that this thick crust would have trapped enough heat from radioactive decay to partially melt the lower crust during Mars’ early history, creating conditions perfect for granite formation.
“Granites aren’t just rocks; they’re geological archives that tell us about a planet’s thermal and chemical evolution,” explains Rajdeep Dasgupta, the Maurice Ewing Professor at Rice University. “The fact that we see evidence for similar magmas on Mars through deep crustal remelting underscores the planet’s complexity and its potential for hosting life in the past.”
The same conditions that could have produced granite might also solve one of Mars’ most perplexing mysteries: how liquid water once flowed on its surface despite the planet’s frigid climate. The study suggests that the thick, heat-generating crust in the southern highlands would have maintained liquid water aquifers just two kilometers below the frozen surface, creating underground reservoirs that could burst forth during volcanic eruptions or meteor impacts.
While finding definitive evidence of these granite formations presents a challenge – they would now be buried beneath billions of years of volcanic basalt and dust – the research team suggests that future Mars missions could focus on deep impact craters in the southern highlands, which might expose these hidden layers of granite.
“Every insight into Mars’ crustal processes brings us closer to answering some of the most profound questions in planetary science, including how Mars evolved and how it may have supported life,” notes Kirsten Siebach, one of the study’s co-authors. “Our research provides a roadmap for where to look and what to look for as we search for these answers.”
Paper Summary
Methodology
The researchers used mathematical models to calculate how hot Mars’ crust would have been at different depths and thicknesses billions of years ago. They considered heat coming from two sources: radioactive elements decaying within the crust and heat rising from Mars’ interior. They then used these temperature calculations to determine whether the conditions would have been hot enough to melt rock and form granite.
Key Results
The models showed that any crust thicker than 50 kilometers would have partially melted between 4 and 3 billion years ago. In the southern highlands, where the crust reaches 60-80 kilometers thick, there would have been a 15-30 kilometer thick partially molten zone. This melting would have produced granite-like rocks, while the heat would have maintained liquid water aquifers beneath a relatively thin frozen surface layer.
Study Limitations
The models assume a uniform composition of Mars’ early crust and use estimates of past heat flow that can’t be directly measured. The researchers acknowledge that their one-layer model is simplified compared to Earth’s more complex crustal structure. Additionally, the effects of possible hydrothermal circulation in the predicted water aquifers could have modified the crustal temperatures somewhat.
Discussion & Takeaways
The study suggests that granite formation on Mars was not only possible but inevitable in regions of thick crust, challenging the assumption that granite formation requires plate tectonics and liquid water on the surface. This could mean that Mars’ geology is more Earth-like than previously thought, just hidden from view. The research also provides a mechanism for how liquid water could have existed on Mars without requiring a warm climate, potentially resolving a long-standing paradox in Mars science.
Funding & Disclosures
The research was funded by NASA grant 80NSSC18K0828. The authors declared no conflicts of interest, and no artificial intelligence was used in writing the manuscript. The work represents a collaboration between researchers from Rice University’s Department of Earth, Environmental and Planetary Sciences and the Lunar and Planetary Institute.
