A new study suggests that Mars, which is now a cold and dry planet, had rivers flowing some three billion years ago. The findings add on the growing list of evidence verifying the existence of water in the Red Planet. 

NASA scientists announced last month that they have the first solid evidence of briny liquid water flowing on Mars, as HNGN previously reported. The Mars Reconnaissance Orbiter (MRO) detected signatures of hydrated minerals in a region where red streaks, an indicator of water presence, were spotted about five years ago.

The new study used the images captured by Mars Curiosity in 2012. Researchers at the University of Pennsylvania spotted round and smooth pebbles from the images, suggesting that there could be a river that once carried these rocks.

"We believe liquid water is a principal ingredient for life," Douglas Jerolmack, study co-author and a geophysicist at the University of Pennsylvania in Philadelphia, told Space.com. "Knowing whether pebbles in a river moved 1 kilometer or 100 kilometers [0.6 miles or 62 miles] could tell us how stable water was on the surface of ancient Mars."

The team computed the travel distance of the pebbles based on their shapes. They developed the quantitative model using the river systems in Earth, including Puerto Rico and New Mexico. They then made necessary adjustments to make it applicable to the Martian rocks.

Their analysis showed that the pebbles had traveled nearly 50 kilometers 30 miles from the source, losing 20 percent of their volume in the process. The researchers determined that the source is the Gale Crater, believed to be formed when a meteor hit the Red Planet about 3.5 to 3.8 billion years old.

“Now we have a new tool we can use to help reconstruct ancient environments on Earth, Mars and other planetary bodies where rivers are found such as Titan,” Jerolmack said in a university news release.

The findings of the study can also be used by scientists to better understand how rocks, such as gold, in Earth, are transported from the source.

The research was published in the Oct. 13 issue of Nature Communications.