Mars' ancient climate remains one of the most perplexing mysteries in our Solar System. Once known for its warm and wet conditions, the planet has transitioned into a dry and cold environment. Recent research indicates that during its cold, early history, sheets of frozen carbon dioxide played a crucial role in facilitating river flows and creating a sea comparable in size to the Mediterranean.

Understanding Mars' Climatic Shifts

Mars's transition from a hospitable environment to its current state was neither abrupt nor the result of a single catastrophic event. Instead, it underwent a series of gradual climatic episodes, showcasing a complex evolution.

The Martian landscape evidences its watery past, with features such as river channels, impact craters, and basins reminiscent of paleolakes. While Mars exhibits significant differences from Earth, both planets operate under similar physical and geological laws.

In regions experiencing frigid climates, rivers may flow beneath thick ice sheets. Evidence suggests that a parallel phenomenon occurred on Mars. The latest work published in the Journal of Geophysical Research: Planets, titled "Massive Ice Sheet Basal Melting Triggered by Atmospheric Collapse on Mars, Leading to Formation of an Overtopped, Ice-Covered Argyre Basin Paleolake Fed by 1,000-km Rivers," sheds light on this topic with lead author Peter Buhler from the Planetary Science Institute.

The Role of Carbon Dioxide on Ancient Mars

This study examines conditions approximately 3.6 billion years ago during Mars's transition from the Noachian Period to the Hesperian Period. It suggests that during this time, much of the surface water was captured in large ice sheets forming in Mars' southern hemisphere. The atmosphere of Mars underwent periodic collapses, leading to the sublimation of CO2. This process resulted in the formation of a substantial CO2 layer, approximately 650 meters (0.4 miles) thick, acting as a giant ice cap over the south pole. It provided insulation to an underlying layer of frozen water that reached depths of about 2.5 miles (4 km).

A schematic showing the CO2 atmospheric collapse on Mars.

A schematic illustrating how the CO2 atmosphere collapses, forming an insulating layer over the frozen water at Mars' southern polar regions. Meltwater is released, flowing across the surface, insulated by a layer of frozen water. Image Credit: Buhler, 2024.

Mechanism of Water Flow on Mars

Peter Buhler's model demonstrates that the CO2 cap acted as a thermal blanket, releasing immense amounts of meltwater from beneath the polar ice. This meltwater subsequently flowed through channels, the upper layers freezing and monopolizing the liquid water beneath.

“You now have the cap on top, a saturated water table underneath and permafrost on the sides,” Buhler explains. “The only way left for the water to go is through the interface between the ice sheet and the rock underneath it.”

Buhler's research indicates that enough water was released to fill the Argyre Basin, one of the largest impact basins on Mars, measuring approximately 1800 km (1100 mi) in diameter. This ancient impact basin, identified as the second deepest on Mars at about 5.2 km (3.2 mi) below surrounding plains, was long thought to have once contained enough water, similar to the Mediterranean Sea.

Evidence of Subglacial Rivers

Evidence for rivers flowing beneath the Martian ice sheets comes from the presence of eskers—long formations created by meltwater streams flowing beneath glaciers. These geological features mirror formations found on Earth, strengthening the claim that subglacial melt occurred on Mars.

Eskers formed by meltwater streams under a glacier in Sweden.

These are eskers found in western Sweden, created by water flowing under a glacier. When the glacier retreated, these formations remained as evidence of previous meltwater flows. Image Credit: By Hanna Lokrantz - Geological Survey of Sweden, CC BY 2.0

As the subglacial rivers flowed under the ice, they were insulated from the frigid air above. The meltwater would have created extensive river channels spanning thousands of miles, some connecting from the polar ice caps to the Argyre Basin. Buhler’s model suggests that this process likely transpired over ten thousand years, during which the waters would repeatedly fill the basin and later drain, creating a continuous loop of hydrological activity.

Flooding of the Argyre Crater by meltwater channels.

This figure depicts the polar cap, the Argyre Crater, and the intricate channels that conveyed meltwater from the cap to the basin. Image Credit: Buhler 2024.

Addressing Long-standing Mysteries

Previously, hypotheses to explain the water's presence in the Argyre Basin often revolved around global warming events. However, Buhler's model, emphasizing atmospheric collapse and subsequent melting due to the CO2 cap, avoids the need for such explanations.

This theory adds to our understanding of the geological dynamics of Mars. The observed valley networks, evidence of erosion and sedimentation from powerful water flows, coincide with the timelines outlined in Buhler's research. The intense fluvial activity during the Late Noachian/Early Hesperian periods offers clues into Mars' hydrological history.

Modern Observations of Mars' Atmospheric Cycles

Buhler draws from contemporary observations of atmospheric CO2 cycles on Mars to support his hypotheses. Martian CO2 is primarily found frozen and bound to the surface regolith. Furthermore, the planet's axial tilt influences the atmospheric pressure and conditions, akin to mechanisms observed on Earth.

Future Research Directions

Buhler aims to rigorously test his model further, which could potentially revolutionize our understanding of Martian hydrology and climate change. This research reinforces the importance of continued exploration and study of Mars, not only through robotic missions but also with a view toward future human exploration.

Conclusion

Our understanding of Mars has evolved significantly due to this recent research, potentially reshaping our conjectures regarding not only its past and climate but the very processes that sustained its ancient rivers. This paradigm shift underscores the unraveling mystery of Mars—the ancient habitable world that captures our imagination and scientific scrutiny.

References

The link has been copied!