Hello everyone! Today we will be looking at the planet Mars–more specifically, the climate of its early history. Modern day Mars shows evidence of past lakes, valley networks, and has minerals and rocks that all point to liquid water on the surface. However, Mars receives less than half the sunlight Earth does, and the sun was not as bright in the past. So how does liquid water occur in such circumstances?
To make inspecting this problem more difficult, there are many unknowns. How long might some sort of warmer episode on Mars have lasted? How much water vapor and carbon dioxide was in the atmosphere? Was early Mars warm and wet, with oceans? Or could Mars have been cold and icy, with seasonal melting?
Enter today’s article: “Comparison of “warm and wet” and “cold and icy” scenarios for early Mars in a 3D climate model” by Robin D. Wordsworth, Laura Kerber, Raymond T. Pierrehumbert, Francois Forget, and James W. Head. Published in the American Geophysical Union’s Journal of Geophysical Research: Planets in 2015, this article uses a 3 dimensional modelling system to look at possibilities for early Mars.
The team ran various simulations of Mars 3.8 billion years ago. While they looked at obliquity angles (the tilt of the north-south line away from the plane of orbit: 23.5 on Earth) from 10 to 55, 41.8 degrees is considered most likely for the time period, and focused on these scenarios when presenting their results.
The warm and wet scenario had an average surface temperature of 282.9 Kelvin–about 50 Fahrenheit, or 8 Celsius. The model showed low precipitation in an area called Margaritifer Sinus. However, this region shows valley networks that suggest erosion by precipitation. The warm and wet scenario was also difficult to obtain in the model–requiring an amount of sunlight that with the fainter, younger sun, Mars should have never seen. The warm and wet scenario, compared to where valley networks are seen on modern Mars, do not match up very well.
In stark contrast, the water-formed features likely from the cold and icy scenario correlate much better with what is seen today, though still imperfect. The average surface temperature in this scenario was 225.5 Kelvin–around -54 Fahrenheit, or -48 Celsius. Most of the snow and ice accumulated in the highlands near the equator (temperature decreases with height, so these regions were some of the coldest on the planet in such simulations). Most of the valley networks are seen in this area. The cold and icy models only showed melting at the equator with obliquity angles greater than 25 degrees–and as mentioned, it is believed to be around 41.8 degrees. The daily maximum temperature was-20 Celsius (-4 Fahrenheit), but effects such as clouds, volcanic, and variations in the orbit could bring it to the freezing point of water. The model has melting estimates lower than what is likely to be needed to produce some of the valley networks, but it is close. A more sophisticated model, especially in terms of clouds and precipitation, may yield a better picture of just how close; the authors call for further study. However, the model results definitely suggest a cold, icy Martian past is much more likely than a warm, wet past.
Bibliography
National Aeronautics and Space Administration. NASA’s Mars Exploration Program: Global Views of Mars. NASA/JPL. 2001. Web.
The source of the image used in today’s article.
Wordsworth, Robin D., et al. “Comparison of “warm and wet” and “cold and icy” scenarios for early Mars in a 3‐D climate model.” Journal of Geophysical Research: Planets 120.6 (2015): 1201-1219.
Today’s main article.
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