early mars

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Mars today shows evidence of flowing water in its past from the presence of delta basins, canyons, and surface mineralogy. The remaining water on Mars today seems to be locked up in ice, but at some point in the early history of the solar system, Mars had flowing rivers, lakes, and even oceans.

The problem with this idea of a warm and wet early Mars is that the sun was fainter in the past, thereby providing even less energy than today to help thaw a frozen planet. One possibility is that early Mars had a much thicker greenhouse atmosphere than today, which could have provided enough additional warming to melt the ice. However, many climate models struggle to provide sufficient warming, even with a dense carbon dioxide atmosphere. Another option is that episodes of volcanic eruptions of meteor impacts could have temporarily warmed Mars long enough for water to flow and carve the fluvial features we see today. However, this type of episodic warming may not provide enough rainfall to carve the martian valleys observed today.

In a recent paper published in Earth and Planetary Science Letters, titled “Climate cycling on early Mars caused by the carbonate-silicate cycle,” my co-authors and I propose that climate cycling between warm and glacial states could have occurred on early Mars, driven by the carbonate-silicate cycle as we discuss in a previous study. For early Mars, the accumulation of greenhouse gases may have risen and fallen in episodic cycles, providing punctuated periods of warmth for carving the martian valleys. Our proposed hypothesis combines the notion of enhanced greenhouse warming with episodic warming, which can potentially be tested by future exploration of the martian surface.

Both Earth and Mars show geologic evidence of flowing liquid water in the distant past, nearly four billion years ago. The presence of liquid water on the surface of these planets is difficult to reconcile with the reduced luminosity of the sun at the time, so scientists have continued to search for possible explanations for the warm climates of early Earth and early Mars. A team of researchers recently suggested that early Earth may have had larger oceans and fewer clouds than today, which would have reflected away less incoming sunlight and might have allowed the planet to remain warm in spite of a fainter sun. Whether or not this solution will pan out for early Earth, it at least suggests the possibility of a similar mechanism on early Mars.

In a recent paper published in Astronomy & Astrophysics, on which I am co-author,
we examine the possibility that reduced reflectivity could have kept early Mars above freezing. We use a computer climate model to calculate the global average temperature at various values of ocean fraction and cloud coverage. We find that our model does indeed produce warm conditions for early Earth, but it fails to do the same for early Mars. In fact, our model can only produce warm conditions if early Mars were nearly entirely covered by oceans and also free of clouds, a result which is unlikely as well as inconsistent with geologic evidence. We conclude that some combination of climate and geochemical mechanisms, as yet unknown, may provide clues for understanding the stability of liquid water on early Mars.

If early Mars did harbor oceans, then the possibility remains that life could have developed. Examining the climates of both Earth and Mars in the past may therefore help in the quest to understand the origin of life. Future Mars exploration missions, as well as continued research on Earth, will slowly shed light on this mystery.

Billions of years ago, the planet Mars appears to have been covered by a liquid water ocean. Geologic evidence of riverbeds, deltas, canyons, and other features in the Martian landscape all suggest that a flowing liquid once meandered on the surface of the red planet. Even so, the fainter young sun at the time, combined with Mars’ orbital distance from the sun, suggests that even a wet early Mars was probably quite chilly.

In a recent paper published in Nature Geoscience, on which I am a co-author, we examine the idea that early Mars featured a cold glacial ocean on its northern hemisphere. This study combines some theoretical climate calculations (which was my contribution) along with a mineralogical analysis to reach this conclusion. In particular, the formation of minerals known as phyllosilicates would have been prevented in a cold ocean, which may explain the scarcity of phyllosilicates observed in the northern martian hemisphere today.

And if oceans did exist on Mars billions of years ago, then perhaps the processes of life also could have arisen in the early history of the red planet. Mars today appears barren and lifeless, but signs of past or present life could very well be lurking beneath the soil. Future Mars missions, and possibly human exploration, will eventually help to uncover this mystery.

Satellites and rovers sent to Mars keep giving us compelling geologic evidence that liquid water flowed on the surface of the red planet in the distant past. Three billion years ago, when oceans may have existed on parts of Mars, the sun was about 30% fainter. Mars today is well below the freezing point of water, so any lakes or oceans would be frozen over. In the distant past, then, this problem is even more pronounced: how was Mars able to stay warm enough to sustain liquid water?

Many attempted resolutions have been proposed to this problem, but none has provided a complete solution for a warm, wet early Mars. In a recent paper published in Earth and Planetary Science Letters, on which I am a co-author, we argue that greenhouse warming by sulfur dioxide could not have kept early Mars warm enough. Sulfur dioxide has been suggested in the literature because it is an effective greenhouse gas, similar to carbon dioxide or methane. However, we show that atmospheric photochemistry with sulfur dioxide leads to the production of sulfate aerosols in the upper atmosphere that absorb incoming sunlight and cool the surface. Thus, sulfur dioxide may have caused net cooling on early Mars, rather than warming.

We’re still trying other mechanisms to explain a warm, wet early Mars. Most likely, it was some combination of processes, including several greenhouse gases and warming by clouds. A negative result for sulfur dioxide is not as exciting as a solution to the early Mars problem, but it’s still a small step forward.

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