They also ran different orbital scenarios, since there isn’t agreement on what the Martian orbit was back then. This includes different axial tilts, which affect the amount of sunlight on the planet’s surface, and eccentricity, which deals with the degree to which a planet’s orbit differs from a perfect circle. A planet with a more eccentric orbit can have more extreme seasons, since it is moving farther from and closer to the sun as it travels along the orbit.
The researchers’ model delivered scenarios showing ice deposits in areas around the valley networks, as well as peak summertime temperatures that were above freezing in the southern highlands region.
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To relate the water runoff to the formation of valley networks, the researchers referred to a 2015 study that Head co-authored with Eliot Rosenberg, an undergraduate at Brown who has since graduated. The study estimated how much water was needed at a minimum to create the valleys. Using that study, along with other researchers’ work on runoff rates and the valley network’s history, Palumbo concluded that Mars would have needed an eccentric orbit to produce enough water for valley network creation.
“This work adds a plausible hypothesis to explain the way in which liquid water could have formed on early Mars, in a manner similar to the seasonal melting that produces the streams and lakes we observe during our field work in the Antarctic McMurdo Dry Valleys,” Head said in a statement. “We are currently exploring additional candidate warming mechanisms, including volcanism and impact cratering, that might also contribute to melting of a cold and icy early Mars.”
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The work appears in the same month that a University of Chicago-led team, which was also trying to figure out how Mars was wet in its ancient past, came up with another explanation: methane. Those researchers suggested that the tilt of the Red Planet’s axis wobbled over time, triggering periods of ice melt and methane release. Over time, enough methane built up in the atmosphere to allow for lake-forming climates.
Separately, NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft is examining another line of evidence for Mars’ wetter days. Some scientists suggest that the atmosphere was thick enough in the ancient past to allow water to flow. Today, water can’t exist at the surface due to the very thin atmosphere. MAVEN is looking at the rate of atmospheric loss over time, which occurs due to processes such as “stripping” — when particles from the sun slam into lighter molecules in the Martian atmosphere, pushing the atmospheric molecules into space.
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