Aug. 3 (UPI) -- The majority of Mars' valleys were carved by ice sheets, not flowing rivers, calling the Red Planet's supposed warm, watery past into question, according to new research published Monday in Nature Geoscience.
"Valley networks on Mars have historically been interpreted as surface water flows, either sourced by surface liquid water or by ground water," study lead author Anna Grau Galofre told UPI.
"The problem is that there are thousands of them and they all have very different morphologies," said Grau Galofre, former doctoral student in the department of earth, ocean and atmospheric sciences at the University of British Columbia.
Earth has similarly diverse valley networks, created by a range of processes. Grau Galofre and her colleagues wondered whether a diversity of processes might be responsible for Mars' varied valley networks, too.
Many of the valleys on Mars reminded Grau Galofre of the subglacial channels found beneath ice sheets on Earth.
"Their patterns, isolation from each other and the fact that some flow uphill, all these are consistent with what we know about subglacial channels on Earth," said Grau Galofre, now a post-doctoral researcher at Arizona State University.
"Introducing this hypothesis then turned out to be a useful perspective to address a longstanding question regarding the climate of early Mars: warm and wet versus cold and icy," she said.
First, Grau Galofre and her research partners performed statistical analysis to identify similarities and differences among valley structures on Mars. After identifying a group of similar-looking valleys not explained by river flows, researchers compared the valleys to subglacial channel patterns found on Devon Island in the Canadian Arctic.
According to researchers, Devon Island -- a cold, dry polar desert -- is as close an approximation of Mars' climate as can be found on Earth.
In total, researchers surveyed more than 10,000 Martian valleys. Only a small percentage of the surveyed valleys featured patterns consistent with surface water erosion, suggesting rivers and lakes were less abundant on early Mars than previously hypothesized.
Though Mars is Earth's closest neighbor, it is considerably farther from the sun. At the time that Mars' valleys were forming, 3.8 billion years ago, the sun was dimmer than it is today. Models suggest Mars would have been quite frigid.
While researchers say evidence suggesting the Red Planet's features were mostly formed by glacial activity isn't surprising, the findings don't preclude freshwater environs, nor the possibility of ancient life.
"I would like to highlight that the study finds both evidence for riverine erosion and subglacial erosion among the valley networks," said Grau Galofre. "Sometimes both origins are represented by channels that are close, implying that the climate on early Mars probably changed considerably through time."
Grau Galofre said she would like to see NASA's Martian rovers take a closer look at the geochemical signatures found in clay found on Mars.
"Clays and other hydrated rocks which have been found on Mars also appear in subglacial environments," she said.
If Mars' ancient climate was erratic, as some evidence suggests, subglacial environs might have offered a haven for microbial life.
"The subglacial environment could provide a stable setting, with readily available water, a temperature without large oscillations, and protection from solar energetic particles and radiation without need for a magnetic field," Grau Galofre said.
Researchers have previously identified microbial communities living in subglacial lakes on Earth.
Grau Galofre said she and her research partners hope further comparisons between valley patterns on Mars and Earth will help more precisely model the Red Planet's ancient climate.