Frozen clues: Mars’ crater deposits reveal a history of shrinking ice volumes through ages

For decades, scientists have been curious about how much water Mars once had and what led to its gradual transformation into the dry planet we see today. A new study published online on September 2, 2025, in the Geology journal, sheds light on this mystery by looking deep inside martian craters, which act like “ice archives” that store a frozen record of the planet’s past. These craters reveal that Mars went through repeated ice ages over hundreds of millions of years; however, with each cycle, the amount of remaining ice decreased steadily.

The study was led by Associate Professor Trishit Ruj from Institute for Planetary Materials, Okayama University, Japan, along with Dr. Hanaya Okuda from Kochi Institute for Core Sample Research, Japan, Dr. Hitoshi Hasegawa from Kochi University, Japan, and Professor Tomohiro Usui from Institute of Space and Astronautical Science, Japan. By studying the glacial landforms preserved in craters between 20°N and 45°N latitude, the team was able to reconstruct how Mars stored and lost its water through time.

Dr. Ruj explains, “Mars went through repeated ice ages, but the amount of ice deposited in craters steadily shrank over time. These icy ‘time capsules’ not only reveal how Mars lost its water but also mark places where future explorers might tap into hidden ice resources.”

To investigate this, the researchers analyzed high-resolution images from NASA’s Mars Reconnaissance Orbiter. They focused on craters with indicative signs of glaciation, such as ridges, moraines (piles of debris left behind by glaciers), and brain terrain (a pitted, maze-like surface formed by ice-rich landforms). By comparing the shapes and orientations of these features with climate models, they found that ice consistently clustered in the colder, shadowed southwestern walls of craters. This trend was consistent across various glacial periods, ranging from approximately 640 million to 98 million years ago.

The results show that Mars didn’t just freeze once—it went through a series of ice ages driven by shifts in its axial tilt, also known as obliquity. Unlike Earth, Mars’ tilt can swing dramatically over millions of years, redistributing sunlight and triggering cycles of ice build-up and melting. These changes shaped where water ice could survive on the planet’s surface. Over time, however, each cycle stored less ice, pointing to a gradual planetary drying.

The team highlights the significance of these findings: “By tracing how Mars stored and lost its ice, this study guides future explorers to water supplies and offers insights that can be applied to Earth’s changing environment.”

The implications of this work extend far beyond understanding martian climate. Hidden ice deposits could be important for future human missions to Mars. Buried ice can be used for drinking water, converted into oxygen for breathing, and split into hydrogen and oxygen to make rocket fuel—a process known as in-situ resource utilization (ISRU). This would allow astronauts to live off the land rather than carry all their supplies from Earth, making long-term missions more practical and affordable.

“Knowledge of long-lived ice deposits helps identify safe and resource-rich regions for future robotic and crewed landings,” notes Prof. Usui.

Beyond space travel, the study also offers lessons for our own planet. The shrinking ice on Mars is a planetary-scale example of climate change, showing how water systems respond to long-term environmental shifts. The same imaging and modeling tools used in this research can also help scientists monitor glaciers, permafrost, and hidden water reservoirs on Earth, where the effects of climate change are already visible. “Mars serves as a natural laboratory for understanding how ice behaves over vast timescales. The insights we gain here can sharpen our understanding of climate processes on Earth as well,” emphasizes Dr. Hasegawa.

In conclusion, the discovery of multi-stage glaciations paints a picture of Mars as a planet that once cycled through periods of icy abundance, only to see its frozen reserves steadily diminish. These findings not only enrich our understanding of Mars’ past but also help chart a path forward for its exploration. By learning from the red planet’s icy history, humanity may one day unlock the resources needed to survive and thrive on another world.

About Okayama University, Japan

As one of the leading universities in Japan, Okayama University aims to create and establish a new paradigm for the sustainable development of the world. Okayama University offers a wide range of academic fields, which become the basis of the integrated graduate schools. This not only allows us to conduct the most advanced and up-to-date research, but also provides an enriching educational experience.

Website: https://www.okayama-u.ac.jp/index_e.html

About Associate Professor Trishit Ruj from Okayama University, Japan

Dr. Trishit Ruj is an Associate Professor at the Institute for Planetary Materials, Okayama University, Japan. He earned his Ph.D. in 2018 from Università "G. d'Annunzio", Chieti-Pescara, Italy, and holds a Master of Science from Presidency College, University of Calcutta, India. With over 6 years of research experience, Dr. Ruj has authored 13 publications, focusing on planetary surface processes, martian ice deposits, and tectonics. He leads the Planetary Geology & Surface Simulation Lab, employing experimental simulations to study planetary environments. Dr. Ruj is a member of the Japanese Society for Planetary Sciences and the Japan Geoscience Union.