New analysis of glacial deposits within craters on Mars indicates the planet has experienced numerous ice ages over hundreds of millions of years, but with a progressively diminishing volume of ice accumulating during each cycle. These findings, based on observations of craters that serve as natural “ice archives,” offer a detailed record of the planet’s climatic history and provide compelling evidence of Mars’ gradual transformation from a world once richer in water to the arid planet known today.
The research suggests a long-term trend of water loss on the Red Planet. By examining preserved glacial features, scientists have pieced together a history of recurring climate shifts driven by changes in the planet’s axial tilt. While Mars has cycled through multiple periods of glaciation, the total amount of ice deposited in its craters has steadily shrunk over geologic time. This discovery provides crucial insights into how and when Mars lost its water and helps identify potential locations for future resource exploration.
Icy Archives in Martian Craters
A team of planetary scientists focused their research on craters located between 20°N and 45°N latitude on Mars. These mid-latitude craters act as protected environments, preserving frozen records of the planet’s past climate. Led by Associate Professor Trishit Ruj from the Institute for Planetary Materials at Okayama University, Japan, the researchers analyzed high-resolution images captured by NASA’s Mars Reconnaissance Orbiter. They looked for specific glacial landforms, including moraines—piles of debris left by glaciers—and distinct surface patterns like “brain terrain,” which is associated with ice-rich deposits.
The study, published in the journal Geology on September 2, 2025, utilized these features to reconstruct the extent of past glaciations. Unlike the planet’s expansive polar ice caps, which are older and have lost finer details over time, the smaller crater deposits provide a fresher and more detailed record of climate variations. By analyzing the morphology of these deposits, the team could infer the intensity and scale of ice accumulation during different geological periods.
A History of Repeated Ice Ages
The investigation revealed that Mars did not experience a single, prolonged freeze but rather a series of distinct ice ages. These climatic cycles are driven by significant variations in the planet’s axial tilt, or obliquity. Unlike Earth, which has a relatively stable tilt thanks to its large moon, Mars’s axis can wobble dramatically over millions of years. These shifts alter the distribution of solar radiation across the planet’s surface, triggering cycles of ice accumulation and subsequent melting or sublimation.
The Obliquity Effect
During periods of high obliquity, increased sunlight at the poles would have caused polar ice to sublimate and travel through the atmosphere, re-depositing as snow and ice in the mid-latitudes, including within craters. As the planet’s tilt decreased, these mid-latitude glaciers would have retreated. The researchers found that ice consistently accumulated in the colder, shadowed southwestern walls of the craters. This pattern was observed across glacial periods spanning from approximately 640 million to 98 million years ago.
Evidence of a Drying Planet
A key finding of the study is the clear trend of diminishing ice volumes with each successive ice age. By comparing the extent of glacial features from different eras, the team determined that the amount of water available to form these glaciers steadily decreased over time. This observation points to a continuous process of water loss from the Martian system, contributing to the planet’s gradual aridification. The research provides a timeline for this drying process, showing that with each climate cycle, less water returned to the craters.
Advanced Methodologies
To reach their conclusions, the researchers combined detailed observations with sophisticated climate models. They analyzed images from the Context Camera (CTX) aboard the Mars Reconnaissance Orbiter, which provides wide-area, high-resolution views of the Martian surface. These images allowed for the identification of subtle glacial features such as ridges, flow patterns, and moraines within numerous craters. The team categorized the crater deposits based on their size and complexity, distinguishing between thin, restricted fills and thicker, more extensive glacial formations.
By comparing the physical evidence with models of past Martian climates, the scientists could correlate the observed glacial deposits with specific periods of the planet’s orbital history. This integrated approach confirmed that the placement and size of the ice deposits matched the expected patterns driven by changes in Mars’ axial tilt. The consistency between the geological evidence and climate simulations strengthens the conclusion that obliquity cycles were the primary driver of Martian ice ages.
Implications for Future Exploration
The study’s findings have significant implications beyond understanding Mars’s ancient climate. Identifying the locations of these long-lived ice deposits is crucial for planning future robotic and human missions. Water is a critical resource for any sustained presence on Mars, and these crater “time capsules” mark potential sites where future explorers might access hidden ice reservoirs. As Professor Usui, a contributor to the study, noted, a detailed knowledge of these deposits can help pinpoint safe and resource-rich landing sites.
Furthermore, the research offers a planetary-scale case study in climate change. Observing the long-term response of Mars’ water systems to environmental shifts can provide valuable insights for understanding similar processes on Earth. The same remote sensing and modeling techniques used to study Martian glaciers can be applied to monitor glaciers, permafrost, and hidden water sources on our own planet, where climate change is an increasingly urgent concern.
