Hello and welcome back, Earthlings!
Glaciers on Mars were quite similar to those of Earth:
-Glaciers are not pure water ice. Many have large amounts of debris and are considered rock glaciers. As glaciers skid across the valleys, they leave rock debris trails behind, like breadcrumbs.
-Formations of moraines are similar in that when a glacier stops movement and potentially melts away, it leaves behind a moraine, or pile of debris and rocks. From the rocky concentrations, we could study how large and direction of the past glacier.
-Formations of valleys. If the glacier is wide enough, it can carve out a traveling valley!
How do we know? Context clues! We look for geologic clues, such as how the terrain has changed, when a glacier has come and gone. We do this on Earth as well- we look for valleys and changes in terrain that a glacier may have once roamed!
Why are there no glaciers present (or at least large ones)? It has been researched that Mars used to have a tilt of 45 degrees, not the present-day 25 degree angle. This would have stabilized larger regions of ice. However, its two small asteroid-like moons do not stabilize its axial tilt and instead wobbles over time. This drastic change, from 45 degrees to 25 degrees, completely sublimated most of the ice regions, leaving Mars with seasonal ice growth and polar concentrations of ice.
Thank you for reading and a surprise awaits next time!