Researchers from Brown University sheds new light on the role of melting ice in the formation of ravine-like channels on Mars. Published in the journal Science, the study focuses on Martian gullies that bear a striking resemblance to gullies found in the Dry Valleys of Antarctica on Earth. These gullies are created by water erosion from melting glaciers. The scientists, including Jim Head, a planetary scientist from Brown University, developed a model that simulates the conditions necessary for Mars to warm above freezing temperatures, resulting in periods of liquid water as ice on and below the surface melts.
The researchers discovered that when Mars tilts on its axis to 35 degrees, the atmosphere becomes dense enough to permit brief episodes of melting at the locations of the gullies. By comparing the data from their model with periods in Martian history when the gullies in the Terra Sirenum region rapidly expanded downhill from higher elevations, the scientists were able to demonstrate that water must have been present to explain this phenomenon.
While it is well-known that Mars had running water on its surface, including valley networks and lakes, during its early history, approximately 3 billion years ago, all of that liquid water was lost, transforming Mars into a hyper-arid or polar desert. However, this study shows that even after this loss and in more recent times, Mars can heat up sufficiently to melt snow and ice when its axis tilts to 35 degrees. As temperatures drop again, the liquid water freezes once more.
These findings provide valuable insights into the formation of Martian gullies, addressing questions such as their starting heights, the extent of erosion, and the distance they travel down crater slopes. Previously, scientists theorized that Martian gullies were carved by carbon dioxide frost, which evaporates from the soil and triggers rock and rubble to slide down slopes. However, the height and erosion of the gullies led many researchers to propose that meltwater from glaciers must have played a role. Establishing the existence of liquid water on Mars since its disappearance billions of years ago has been challenging due to the planet’s typical sub-freezing temperatures, which hover around 70 degrees below freezing.
According to the latest study, gully formation on Mars was influenced by both periods of melting ice and evaporation of CO2 frost during other parts of the year. The researchers discovered that this process likely occurred repeatedly over the past several million years, with the most recent instance taking place approximately 630,000 years ago.
The study’s lead author, Jay Dickson, who was previously affiliated with Brown University and is now at the California Institute of Technology, explained that if ice was present at the gully locations they examined when Mars’ axis tilted to around 35 degrees, the conditions would have been suitable for the ice to melt due to temperatures rising above 273 Kelvin (equivalent to about 32 degrees Fahrenheit).
Dickson emphasized that the global distribution of gullies on Mars can be better explained by the presence of liquid water within the last million years, in contrast to CO2. He stated that Mars has been capable of producing sufficient volume of liquid water to erode channels in recent geological history, which is relatively recent on Mars’ timescale.
Despite previous doubts and difficulties in modeling the conditions required for ice to melt on Mars, the researchers were convinced of the accuracy of the meltwater theory due to firsthand observations of similar features in Antarctica. Despite the cold temperatures there, the sun can heat the ice just enough to induce melting and gully activity.
This study builds upon previous research conducted by the team over several decades, investigating Martian gullies. Their earlier study in 2015 suggested that there may have been periods in Mars’ history when water was available for gully formation if the planet experienced sufficient tilting on its axis. These findings motivated them to model the specific tilt angles and match them with the locations and altitudes of the formed gullies.
The paper also raises the fundamental question of the potential existence of life on Mars, as liquid water is closely associated with life as known on Earth. The researchers note that Mars will eventually tilt to 35 degrees again, opening up possibilities for environments that could support the formation, preservation, and continuation of life. Exploring these gullies during future missions to Mars is considered crucial, as they present potential targets for investigation.
Source: Brown University