New geochemical models reveal that feldspar-rich Martian rocks interacting with carbon-dioxide-rich groundwater could resolve the planet’s long-standing missing carbonate mystery. Researchers from JAXA and affiliated institutions demonstrate that subsurface percolation efficiently buries carbonates deep underground, pointing future drilling missions toward hidden stores of Mars’ watery history.
Geochemical Simulations and the Feldspar Pivot
For decades, planetary scientists have faced a glaring contradiction in Martian data. Consensus models show that early Mars possessed abundant surface water, flowing rivers, and a thick, carbon-dioxide-rich atmosphere. Yet, orbiters and rovers have mapped only a fraction of the carbonate rocks expected under such conditions. Traditional hypotheses assumed that ancient water interacted primarily with mafic, iron- and magnesium-rich minerals.
A geochemical study led by doctoral student Chang-Chin Wang, alongside Professor Tomohiro Usui of the Institute of Space and Astronautical Science at JAXA and the University of Tokyo, and Associate Professor Mohit Melwani Daswani from the Earth-Life Science Institute (ELSI) at the Institute of Science Tokyo and the SETI Institute, challenges this baseline. Published in the journal JGR Planets, their research explores whether feldspar-rich rocks—which make up 60% of Earth’s crust and appear increasingly in Martian mission data—hold the missing link.
To test this, the team constructed one-dimensional thermochemical models using the PHREEQC Version 3 geochemical code. These simulations tracked aqueous reactions ranging from short bursts to 100,000-year episodes under early Martian parameters. The code evaluated two modes of water movement: static diffusion and downward groundwater percolation.
Unlocking Calcium and Iron-Rich Carbonate Formations
The simulations revealed a distinct behavioral split between mineral types. While mafic rocks produced calcium/iron-rich carbonates only during brief initial alteration phases before shifting entirely to magnesium-rich minerals, feldspar-rich rock reliably generated calcium- and iron-rich carbonates across nearly all tested conditions. This structural divergence explains why surface detections have been scarce and chemically distinct.
More critically, the thermochemical runs demonstrated that percolating groundwater outperformed standing surface water in carbonate generation. As groundwater flowed downward, it dissolved surface carbonates near the upper crust and reprecipitated them deep below the surface. This continuous hydrological cycling suggests that massive stores of carbonate rocks remain hidden beneath the Martian crust, directly mirroring theories regarding the planet’s missing water inventory.
The Jezero Crater Mineral Crossroads
This subsurface geochemical activity aligns closely with on-the-ground discoveries made by robotic explorers. When NASA’s Perseverance rover reached the Margin Unit along the shoreline of an ancient Martian lake inside Jezero Crater in September 2023, mission scientists anticipated layers of sedimentary clay and silt. Instead, they encountered igneous rock that preserved a complex record of water activity across at least three distinct episodes.
Using the mast-mounted SuperCam instrument to fire lasers up to 21 feet away, the rover analyzed the light spectrum of resulting bedrock targets. Candice Bedford, a research scientist at Purdue University and lead author of a related study published in Communications Earth & Environment, noted that the location functioned as a critical crossroads for aqueous systems. At higher elevations, the rover encountered coarse-grained olivine untouched by water, while lower lakebed rocks showed olivine grains fractured and packed with silica and carbonates.
Eleni Ravanis, a planetary scientist at the University of Hawaii at Manoa and coauthor of the Jezero Crater study, highlighted the dual presence of silica and carbonates in these formations. On Earth, such mineral pairings act as vital signposts for tracking ancient life, as water-olivine interactions release hydrogen that can serve as microbial energy sources while locking chemical traces into mineral structures.
Implications for Future Subsurface Exploration
The convergence of JAXA’s geochemical modeling and Perseverance’s in-situ spectroscopy reframes how planetary scientists view the Martian interior. Because groundwater actively dragged and sequestered carbonates deep out of orbital sight, the current barren appearance of the surface is an artifact of downward hydrological transport rather than a total absence of ancient aqueous activity.
Future missions targeting Mars will rely heavily on underground aquifers for sustained exploration and resource utilization. According to the JAXA-led team, drilling operations focused on feldspar-rich terrains will provide the most reliable access point for recovering physical evidence of the planet’s warm, wet youth and locating the water that retreated underground as the climate dried billions of years ago.
