Mars was Warm and Wet 3.7 Billion Years Ago, New Study Suggests

Planetary scientists have discovered more than 15,000 km of ancient rivers beds in Noachis Terra, a Highlands region in the south of March. This discovery suggests that Mars could have been much more humid than we thought before.

This Hrise image shows a strongly eroded river crest on Mars; Sand dunes can be seen migrating above the river winding ridge. Image credit: NASA / JPL / University of Arizona.

The nature of the Martian climate during the Noachian-Hesperian transition, a period of geological and climatic changes around 3.7 billion years, and how surface characteristics such as valley networks and lakes associated with liquid water formed are debated.

There are two theories: the first is that the hot and humid conditions persisted on early Mars long enough for liquid water to be stable on the surface for long periods; The second is that Mars was generally cold and dry, and that geological characteristics indicating flowing water were formed only very sporadically by the cast iron water of the glacial caps during short climatic excursions.

Noachis Terra is a region where “hot and humid” climatic models predict high rates of precipitation.

In new research, Open University PH.D. The student Adam Losekoot and his colleagues examined the winding river ridges, also known as inverted channels, in this region.

“These have formed when sediments deposited by rivers harden and were later exposed as the surrounding material was eroded,” the authors said.

“Similar ridges have been found on a range of land on Mars.”

“Their presence suggests that the flowing water was once widespread in this region, precipitation being the most likely source of this water.”

They found that the winding river ridges were common through Noachis Terra, with a cumulative length of more than 15,000 km.

These are often isolated segments, but some systems measure hundreds of kilometers.

“The Mars study, in particular an under-explored region like Noachis Terra, is really exciting because it is an environment that has been largely unchanged for billions of years,” said Losekoot.

“It is a temporal capsule that records fundamental geological processes in a way that is simply not possible here on earth.”

For the study, the researchers used data from three orbital instruments: the context camera (CTX), the laser altimeter of Mars Orbiter (MOLA) and the Scientific Experience of High Resolution imaging (Hrise).

These data sets have enabled them to map the locations, lengths and morphologies of crest systems in a large area.

“Our work is a new evidence that suggests that Mars was once a much more complex and active planet than now, which is such an exciting thing to get involved,” said Losekoot.

“The fact that the ridges form large interconnected systems suggest that the aqueous conditions must have been relatively long, which means that Noachis Terra has experienced hot and humid conditions for a geologically relevant period.”

“These results question the existing theories according to which Mars was generally cold and dry, with some valleys formed by cast iron water in the sporadic, short periods of warming.”

Scientists presented their results on July 10 at National meeting of astronomy of the Royal Astronomical Society 2025 In Durham, the United Kingdom.

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Adam Lostkoot and al. The river history of Noachis Terra, March. NAM 2025