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News — PROVIDENCE, R.I. [Brown University] —A recent study conducted by a team of researchers from Brown University has provided fresh insights into the role of melting ice in the formation of ravine-like channels within impact craters on Mars.

Published in the journal Science, the study focuses on the peculiar gullies found on Mars, which bear a striking resemblance to the gullies formed by water erosion in Antarctica's Dry Valleys due to melting glaciers. Led by planetary scientist Jim Head from Brown University, the researchers developed a model that replicates the favorable conditions on Mars when the planet's temperature rises above freezing point, leading to periods of liquid water as the ice on and below the surface melts.

By analyzing the data from their model, the scientists discovered that when Mars tilts on its axis to an angle of 35 degrees, the atmosphere becomes sufficiently dense for intermittent melting episodes to occur in the gully regions. They then correlated the data with specific periods in Mars' history when the gullies in the Terra Sirenum region experienced rapid expansion downhill from higher elevations. This phenomenon could only be explained by the presence of water at certain intervals.

Jim Head, a geological sciences professor at Brown University, explained, "Through our research and that of other scientists, we have come to understand that Mars once had flowing water on its surface, with river valleys and lakes. However, approximately 3 billion years ago, all of that liquid water was lost, and Mars transformed into what we now refer to as a hyper-arid or polar desert. Nevertheless, our study demonstrates that even after this transition and in more recent times, when Mars tilts to an angle of 35 degrees, it warms up sufficiently to melt ice and snow, reintroducing liquid water until temperatures drop and it refreezes."

The recent findings provide valuable insights into the formation of Martian gullies, shedding light on crucial aspects such as their starting points, erosion intensity, and extent down the crater slopes.

Earlier theories proposed that carbon dioxide frost played a role in carving the gullies. It was believed that the frost evaporated from the soil, causing rocks and debris to slide down the slopes. However, the height and erosion patterns of the gullies led many scientists to speculate that the involvement of meltwater from glaciers was necessary, considering the distance the gullies traveled down the slopes and their eroded appearance. The challenge in confirming the presence of liquid water on Mars stemmed from the extremely cold temperatures, which usually hover around 70 degrees below freezing.

The findings of the new study suggest that gully formation was driven by a combination of ice melting and the evaporation of CO2 frost during different parts of the year. The researchers discovered that this process likely occurred repeatedly over the past several million years, with the most recent occurrence estimated to be approximately 630,000 years ago.

According to the researchers, the presence of ice at the gully locations they examined on Mars, coupled with a tilt of the planet's axis to approximately 35 degrees, created favorable conditions for ice to melt due to temperatures rising above 273 degrees Kelvin (equivalent to about 32 degrees Fahrenheit).

Lead author Jay Dickson, who conducted the study while at Brown University and is currently affiliated with the California Institute of Technology, stated, "Our study demonstrates that the distribution of gullies worldwide is better explained by the presence of liquid water in the past million years. Water provides a more plausible explanation for the elevation distribution of gullies compared to carbon dioxide. This implies that Mars has had sufficient liquid water, within the last million years, to cause channel erosion, which is relatively recent in Mars' geological history."

Despite initial skepticism regarding the possibility of meltwater and the inability to replicate the necessary conditions for ice melting on Mars, the researchers were convinced of the accuracy of the meltwater theory due to their firsthand observations of similar features in Antarctica. Despite the frigid temperatures, the sun's heat is capable of melting ice and triggering gully activity in Antarctica.

This new study builds upon previous research conducted by the team over several decades, focusing on Martian gullies. For instance, in a study from 2015, the researchers demonstrated the potential existence of periods in Mars' history when water could have been present to form gullies, depending on the tilt of Mars' axis. These findings motivated them to model the specific tilt angle and correlate it with the locations and altitudes of the formed gullies.

The research paper raises a fundamental question regarding the possibility of life on Mars, as the presence of liquid water is closely associated with life as we know it on Earth. The researchers note that Mars will eventually tilt to 35 degrees once again.

Jim Head, one of the researchers, poses the question, "Could there be a connection between the early warm and wet Mars and the Mars we observe today, in terms of the presence of liquid water?" Scientists are constantly searching for environments that could support not only the formation of life but also its preservation and continuity. Any microorganisms that might have evolved on early Mars would likely thrive in locations where they can survive comfortably in ice and also prosper in liquid water. In the extreme cold of the Antarctic environment, for instance, the few organisms that exist often remain in a state of stasis, awaiting the presence of water.

Additionally, the study emphasizes the significance of these gullies as potential targets for future exploration missions to Mars.