Polar regions

Lore & Background

The polar regions receive less intense solar radiation than other parts of Earth because the Sun's energy arrives at an oblique angle, spreading over a larger area and traveling a longer distance through the atmosphere. The axial tilt of Earth (23.5°) has the most effect on polar climate, but because these regions are farthest from the equator, they remain frigid year round. Ice and snow further reflect and weaken the already weak sunlight, contributing to the cold.

Reader's Guide

The polar regions are significant as Earth's coldest and most extreme climatic zones, influencing global climate patterns and hosting unique ecosystems. The Arctic region contains diverse human settlements and cultures, with countries such as the United States, Canada, Denmark, Norway, Finland, Sweden, Iceland, and Russia claiming territories. In contrast, the Antarctic has no permanent human habitation but supports a complex ecosystem, particularly along coastal zones where upwelling provides nutrients for krill, which in turn feed penguins and blue whales. These regions are also critical for scientific research, with stations like McMurdo Station (US), Esperanza Base (Argentina), and Vostok Station (Russia) operating in Antarctica.

Did You Know?

• The Arctic has various definitions, including north of the Arctic Circle (66°33'44" N) or north of 60° north latitude.
• The Antarctic is usually defined as south of 60° south latitude or the continent of Antarctica.
• McMurdo Station is the largest research station in Antarctica, run by the United States.
• Coastal upwelling in Antarctica provides nutrients that feed krill, which in turn feed penguins and blue whales.

The Great Seasonal Breathing

The most dramatic feature of Mars's polar regions is the annual cycle in which a substantial fraction of the planet's entire atmosphere literally freezes out and then returns. During each winter, roughly 3 to 4 trillion tons of carbon dioxide condense onto the pole facing away from the Sun, representing 12 to 16 percent of the total atmospheric mass. The frozen CO2 settles as a thin slab—about a meter thick over the northern cap—resting atop kilometer-deep water ice permafrost in continuous darkness. When sunlight returns in spring, the dry ice sublimates directly back into gas, and the atmosphere re-inflates. This cycle also drags along vast quantities of dust and water vapor, producing frost patterns and cirrus-like clouds that give Mars a fleeting resemblance to Earth's weather. Scientists have even detected minute shifts in Mars's gravity field caused by this seasonal mass transfer between the poles.

Architecture of the Caps

Both Martian polar caps are built primarily from water ice, yet they differ markedly in scale and elevation. The northern cap, spread across a diameter of roughly 1,000 km during its summer, holds an estimated 1.6 million cubic kilometers of ice—comparable to the 2.85 million cubic kilometers stored in Earth's Greenland ice sheet. Its base sits at about minus 5,000 meters, making it a low-lying, relatively warm feature where all seasonal dry ice vanishes each summer. The southern cap is far more compact, only 350 km across but 3 km thick, perched at elevations between 1,000 and 3,500 meters, and retains a permanent dry ice blanket roughly 8 meters thick. Both caps display striking spiral troughs. Radar data from the SHARAD instrument revealed that these spirals are carved by katabatic winds flowing downhill from the cap's center, deflected by the Coriolis Effect into a rotating pattern. Layered deposits of ice and dust, laid down seasonally over geological time, record past climate in a manner analogous to tree rings or terrestrial ice cores.

Geyser Eruptions and Spider Patterns

Near the southern cap, a process unlike anything commonly seen in planetary geology unfolds each spring. During winter, transparent slabs of dry ice up to a meter thick form over the ground. As sunlight returns, it warms the subsurface, and pressure from subliming carbon dioxide builds beneath the slab until it lifts and ruptures. The result is a geyser-like burst of CO2 gas mixed with dark basaltic sand and dust, erupting from beneath the ice. What makes this phenomenon especially remarkable is its speed: the entire cycle can occur over just days, weeks, or months—a rate of change that is extraordinary by geological standards, particularly on a planet where most surface processes unfold over millions of years. The gas rushing beneath the slab toward the eruption site carves a distinctive spider-like network of radial channels in the terrain below. These patterns, observed by orbiting spacecraft, provide a vivid record of a rapid, seasonal, and entirely reversible geological process unique to the Martian south polar region.

Whispers of Ancient Oceans

The polar ice of Mars may hold the key to the planet's wettest past. In March 2015, an international team using ESO's Very Large Telescope, the W. M. Keck Observatory, and NASA's Infrared Telescope Facility mapped isotopic signatures of water in the Martian atmosphere over six years. Their findings revealed that the north polar cap ice is roughly eight times more enriched in deuterium—a heavier hydrogen isotope less susceptible to escape into space—than Earth's ocean water. This implies Mars has shed a volume of water 6.5 times greater than what remains in its present-day polar caps, enough to have filled a global ocean at least 137 meters deep, potentially covering 20 percent of the planet's surface in places nearly a mile deep. Adding to this picture, in 2018 Italian researchers reported radar reflections suggesting a subglacial lake 1.5 km beneath the southern polar layered deposits, roughly 20 km across. If confirmed, it would be the first stable body of liquid water identified on Mars, though the reflections could equally indicate solid minerals or saline ice.