Water may have flowed on ancient Mars in peak summers, even though the red planet was generally frozen over, a study suggests.
For scientists trying to understand what ancient Mars might have been like, the red planet sends some mixed signals.
While water-carved valleys and lakebeds leave little doubt that water once flowed on the surface, climate models for early Mars suggest average temperatures around the globe stayed well below freezing.
The study led by scientists at Brown University in the US offers a potential bridge between the "warm and wet" story told by Martian geology and the "cold and icy" past suggested by atmospheric models.
The study, published in the journal Icarus, shows that it is plausible, even if Mars was generally frozen over, that peak daily temperatures in summer might sneak above freezing just enough to cause melting at the edges of glaciers.
That meltwater, produced in relatively small amounts year after year, could have been enough to carve the features observed on the planet today, the researchers conclude.
"We see this in the Antarctic Dry Valleys, where seasonal temperature variation is sufficient to form and sustain lakes even though mean annual temperature is well below freezing," said Ashley Palumbo, PhD student at Brown University.
"We wanted to see if something similar might be possible for ancient Mars," said Palumbo.
The researchers started with a state-of-the-art climate model for Mars - one that assumes an ancient atmosphere composed largely of carbon dioxide as it is today.
The model generally produces a cold and icy early Mars, partly because the Sun's energy output is thought to have been much weaker early in solar system history.
The researchers ran the model for a broad parameter space for variables that may have been important around four billion years ago when the iconic valley networks on the planet's southern highlands were formed.
While scientists generally agree that the Martian atmosphere was thicker in the past, it is not clear just how thick it actually was.
Likewise, while most researchers agree that the atmosphere was mostly carbon dioxide, there may have been small amounts of other greenhouse gases present.
Researchers ran the model with various plausible atmospheric thicknesses and extra amounts of greenhouse warming.
The model produced scenarios in which ice covered the region near the location of the valley networks.
While the planet's mean annual temperature in those scenarios stayed well below freezing, the model produced peak summertime temperatures in the southern highlands that rose above freezing.
The results offer a potential means of reconciling the geological evidence for flowing water on early Mars with the atmospheric evidence for a cold and icy planet, researchers said. (PTI)
An appeal from Swarajya
At Swarajya, we rely on our readers' support through subscriptions to sustain our media platform. Unlike larger conglomerates, we are unable to relentlessly chase advertising money — our model is largely built on your patronage.
Your support has never been more crucial. We work tirelessly to deliver 10-15 high-quality articles daily, ensuring you receive insightful content from 7 AM to 10 PM.
If you believe India's story has to be articulated in a way it has never been done before without shrugging it off, become a patron (or) subscribe now for ₹̶2̶4̶0̶0̶ ₹1999 and get 12 print issues, unlimited digital access for 1 year, a special India that is Bharat T-shirt (Offer ends soon).
We are counting on you!