Short answers, pulled from the story.
Each Martian polar cap holds roughly 1.6 million cubic kilometers of water ice. Radar measurements of the north polar layered deposits put that cap's ice volume at 821,000 cubic kilometers, equal to 30 percent of Earth's Greenland ice sheet.
Each spring, sunlight warms the ground beneath transparent 1-meter-thick slabs of dry ice near the south pole. Pressure from subliming carbon dioxide builds until the slab ruptures, producing geyser-like eruptions of gas mixed with dark basaltic sand. The process can unfold over just a few days, weeks, or months.
In 2018, Italian scientists reported that radar reflections from Mars Express may indicate a subglacial lake about 1.5 kilometers below the surface of the southern polar layered deposits and roughly 20 kilometers across. The finding is unconfirmed; the reflections may come from solid minerals or saline ice rather than liquid water.
An international team measured the ratio of deuterium-bearing water to ordinary water in the Martian atmosphere above the north polar cap over a six-year period using three observatories. Results published in March 2015 showed the polar ice is about eight times as enriched with deuterium as Earth's ocean water, indicating Mars has lost a volume of water 6.5 times greater than what remains in the polar caps today.
The southern residual cap is displaced from the geographic pole because a low-pressure weather system generated by the Hellas Basin causes significantly more snow to fall on one side of the pole than the other. Snow reflects more sunlight and sublimates less, while rougher frost on the opposite side absorbs more sunlight and sublimates faster, creating an asymmetric cap.
The layered deposits record alternating periods of dust and ice accumulation driven by changes in Mars's axial tilt over time. Radar data from NASA's Mars Reconnaissance Orbiter correlated the pattern of high- and low-reflectivity layers with climate models. A paper published in Nature in 2023 identified an abrupt brightness change in the northern cap layers dating to roughly 0.4 million years ago, linked to a shift in wind direction recorded in dune patterns studied by the Zhurong rover.