What is the composition of Mars's polar ice caps?
Mars's polar ice caps consist of permanent features made of water ice and dry carbon dioxide. Above kilometer-thick layers of water ice permafrost, slabs of dry ice deposit during a pole's winter.
Questions about Martian polar ice caps
Short answers, pulled from the story.
How large are the northern and southern polar ice caps on Mars?
The northern cap spans about 1000 km in diameter during summer and holds roughly 1.6 million cubic kilometers of ice. The southern cap measures 350 km across with a thickness of 3 km and also reaches a total volume of 1.6 million cubic kilometers including adjacent layered deposits.
When did scientists discover evidence of liquid salt water under Mars's south pole?
In July 2018, ESA discovered indications of liquid salt water buried under layers of ice and dust using radar pulses from Mars Express. Measurements taken in 2018 suggested a subglacial lake exists below the southern polar layered deposits rather than directly under the visible permanent ice cap.
Why do geyser-like eruptions occur at the Martian south pole?
Sunlight warms subsurface layers during spring causing pressure from subliming CO2 to build up under slabs. This process elevates and ruptures the ice creating geyser-like eruptions of gas mixed with dark basaltic sand within days, weeks, or months.
What does the deuterium ratio reveal about Mars's past water history?
Evidence obtained from measuring HDO to H2O ratios over the north polar cap suggests Mars once held enough water to create a global ocean at least 137 meters deep. An international team published results in March 2015 showing polar cap ice is about eight times as enriched with deuterium as Earth's oceans.