Mars haunts us as a vision of a planet gone wrong. It was once warm and wet, with rivers flowing across its surface and (potentially) simple life residing in its water bodies. Now it's dry and freezing.
Could Earth suffer this fate? Are there innumerable other worlds throughout the Universe that were habitable for a period of time before becoming uninhabitable? To answer those questions, we have to answer one of the big questions in space science: What drove the changes on Mars? New research shows that hydrogen played a critical role in keeping ancient Mars warm for periods of time, as the planet's temperature oscillated between warm and cold.
Introduction to the Study
The research titled "Episodic warm climates on early Mars primed by crustal hydration", published in Nature Geoscience, has been conducted by Danica Adams, a postdoctoral fellow in the Department of Earth and Planetary Sciences at Harvard University. Adams noted,
“Early Mars is a lost world, but it can be reconstructed in great detail if we ask the right questions.”
Evidence for Warm Periods on Mars
There’s ample evidence of flowing surface water on ancient Mars. For instance, NASA's Perseverance rover is currently exploring Jezero Crater, an ancient paleolake with significant sediment deposits indicative of flowing water. Satellite images reveal numerous ancient river channels and clear indications of ancient lakes.
For a long time, the dominant scientific thought was that Mars was once warm and then became cold. Recent evidence, however, suggests that Mars oscillated between being a warm and a cold planet. This leads to the question: What drove those oscillations?
- Evidence of flowing water can be found in ancient river channels and lakebeds.
- NASA rovers have significantly contributed to our understanding of Mars' past climate.
- Research indicates that constancy in atmospheric composition played a role in maintaining or changing the temperature.
The Faint Young Sun Paradox
A critical challenge in explaining early warm periods on Mars lies in what scientists refer to as the faint young Sun paradox. The young Sun is believed to have emitted only 70% of the energy it does presently. So, how could Mars have sustained liquid surface water with such low solar output?
“It’s been such a puzzle that there was liquid water on Mars, because Mars is further from the sun, and also, the sun was fainter early on,” said lead author Danica Adams in a press release.
Prior studies suggest that during the late Noachian period, Mars had enough water potentially to form an equivalent global ocean resulting in depths ranging from 100 meters to 1500 meters. Satellite observations have detected lakebeds from that era that rival the size of Earth's Caspian Sea.
The Role of a Hydrogen-Rich Atmosphere
However, it seems unlikely that Mars could have maintained sufficient liquid water under such conditions without a more efficient heat-trapping atmosphere. Carbon dioxide (CO2) alone couldn't achieve this, but researchers propose that hydrogen-rich atmospheres could have provided the necessary warming effect.
The challenge lies in the fact that hydrogen doesn't tend to persist in atmospheres. As noted in the study,
“Greenhouse gases such as H2 in a CO2-rich atmosphere could have contributed to warming through collision-induced absorption, but whether sufficient H2 was available to sustain warming remains unclear.”
Mars' Climate Cycle
If a consistent source of hydrogen existed, it could explain how Mars transitioned between cold and dry to warm and wet periods. The researchers employed a combined photochemical and climate model to simulate how the Martian atmosphere reacted to these climate variations and its interactions with the planet's rocky crust.
According to Adams and her research team, early Mars exhibited two distinct climate states that endured over long timescales. The warm climate could maintain surface liquid water, lasting between 100,000 to 10 million years. These warm phases are attributed to the hydrogen released by crustal hydration, which is occasionally supplemented by volcanic activity. During crustal hydration, water infiltrates the ground and releases hydrogen into the atmosphere.
Hydro-Chemical Modelling of Early Mars
The research team's models indicate that Mars' climate oscillated for about 40 million years throughout the Hesperian and Noachian periods. Each warm phase persisted for at least 100,000 years, correlating with the time it took to carve Mars' river valleys.
This figure from the paper illustrates Mars' H, C, and O chemistry, including ground sinks and escape processes. Image Credit: Adams et al. 2025.
The atmospheric chemistry also varied throughout these periods. When sunlight struck CO2, it transformed into CO. In warm intervals, CO cycled back into CO2, causing both CO2 and H2 to dominate.
Redox State Fluctuations
In simpler terms, the redox state of the atmosphere fluctuated extensively over time. The study’s authors elaborate,
“We’ve identified the time scales for all of these alternations, and we’ve described all the pieces in the same photochemical model.”
Current Martian conditions reinforce the research team's alternating atmospheric redox theory. The surface showcases a paucity of carbonates, which the study argues can only develop in a CO2-dominated atmosphere with neutral pH water when adequate open-system crustal alterations occur.
The Absence of Carbonates on Mars
Carbonates were first discovered on Mars in 2008, with expectations of extensive deposits; however, these large deposits were never located. The research team questions how Mars could have had ample water for prolonged periods while lacking significant carbonate formations.
Surface Evidence Supporting the Study
Mars' surface rocks contain both oxidized and reduced species of minerals, presenting compelling evidence for significant environmental fluctuations. The authors explain,
“While both oxidized and reduced species may form under one climate, the deposition rate of different species is sensitive to the climate. For example, warm climates preferentially deposit nitrate while cool climates preferentially deposit nitrite.”
The lack of carbonates, combined with observations of oxidized and reduced minerals, supports the theory that early Mars underwent extensive variations in climate and atmosphere. Advanced models are anticipated to shed further light on the evolution of Mars in relation to these findings.
Conclusions and Future Directions
In summary, the interplay between hydrogen emissions from crustal hydration and atmospheric chemistry might well account for the variability in Martian climate over millions of years. Understanding Mars' past strengthens our insight into planetary evolution and π habitability.
Future explorations and sample-return missions will be critical for testing the hypotheses raised in this research. Understanding how planets can evolve while retaining or losing habitability will only enhance our knowledge as we continue to explore the cosmos.
For More Information
To learn more about Mars and the studies being conducted, visit these resources:
- Nature Geoscience - Episodes of Warm Climates on Early Mars
- Mars Category on Universe Today
- Harvard University Press Release on Discovery
- NASA Mars Science Laboratory
- NASA's Eridania Sea Image
Stay tuned to Universe Today for ongoing developments in Mars research and advancements in planetary science.
