It has been scientifically proven that Mars was once a very different place with a denser atmosphere, higher temperatures and once water flowing. Evidence of this past is preserved on countless surfaces, from riverbeds and alluvial deposits to lagoon lakes.

However, about 4 billion years ago, the planet began to evolve into what we see today, an extremely cold and dry environment. Also, Mars may have had glacial and interglacial periods, as evidenced by images like the image taken by NASA’s Mars Reconnaissance Orbiter (MRO) shown above.

Evidence of glaciers on Mars includes Earth-like landforms formed by the retreat of ice currents during interglacial periods. While most of the surface ice on Mars is confined to the polar caps, these landforms can be found in nonpolar regions across the planet. This feature was photographed by the High Resolution Imaging Spectroradiometer (HiRISE), the main camera on the MRO. The full-size image (below) offers a wider perspective and shows the glacial deposit flowing downstream.

The black-and-white image is 5 km (3 mi) in diameter and shows linear ridges along the surface, exposed rock debris, and fillings on the floor of nearby craters and valleys. This is similar to what is seen on Earth, where glaciers take rocks and soil from the land and transport them to their surface and below the surface. This allows “rock glaciers” to accumulate material as they gradually retreat and flow downward over thousands of years (or longer). This process creates a network of linear models that scientists use to learn more about the history of ice flows.

These features indicate that Mars, like Earth, experiences periods of cooling and warming that coincide with periodic climate changes. This can coincide with fluctuations in the axial tilt (inclination) of Mars, which is similar to Earth’s orientation – 25° versus Earth’s 23.4° tilt. During colder periods, glacial currents advanced, expanded and collected debris from the land, and then glaciers retreated as ice disappeared through melting and sublimation. Over time, this process left condensed rocks and minerals along long ridges and piles of material in the lowlands.

These images remind us of the highly dynamic climate of Mars, which continues today despite all the changes it has undergone. These changes began about 4 billion years ago, when the core of Mars, which is thought to have stopped its global magnetic field, began to cool rapidly. Since then, Mars’ warmer, denser atmosphere has been gradually destroyed by the solar wind, leading to global cooling and gradual loss of surface water. This resulted in Mars becoming the extremely cold and dry environment we see today.

Ironically, this transit provided excellent preservation of evidence for Mars’ warmer and wetter past. Without precipitation and stronger winds (requiring a dense atmosphere and water circulation), these objects did not undergo weathering and erosion as they do on Earth. Like river channels, clay minerals and alluvial deposits, these preserved ridges prove that glaciers once existed on Mars beyond the polar regions. Source