Martian polar ice caps

Mars has ice at its ends.

This ice is made of water and frozen air.

In the winter, the cold air turns into ice. This makes the ice caps grow.

In the summer, the sun warms the ice. The frozen air turns back into gas.

The ice has many layers. These layers hold dust from storms. They tell us about the past.

Some parts look like Swiss cheese.

These are pits and bumps on the ice. It is a very interesting place.

Mars has two large ice caps at its poles.

These caps are made of water ice. They also have dry ice. Dry ice is frozen carbon dioxide, which is a gas in the air.

In the winter, the poles get very cold. Much of the air freezes onto the ground. This makes the ice caps grow.

In the summer, the sun warms the ice. The dry ice undergoes sublimation. This means it turns directly from a solid into a gas.

The ice caps have many layers. These are called polar-layered deposits. They are made of ice and dust from storms. These layers help us learn about the past climate of Mars.

Sometimes, gas builds up under the ice. This gas can burst out like a geyser. It carves strange, spider-like patterns in the ground.

Scientists think Mars once had a very large ocean. The ice caps hold clues to that lost water.

Mars has two permanent ice caps at its north and south poles.

These caps are made mostly of water ice. They also have layers of dry ice, which is frozen carbon dioxide. The north cap is much larger than the south cap.

It has a diameter of about 1,000 kilometers. This cap contains about 1.6 million cubic kilometers of ice. The south cap is smaller, with a diameter of 350 kilometers. It has a thickness of about 3 kilometers. These ice caps are very important for understanding the planet.

The way these caps change depends on the seasons. Mars has seasons because its axis is tilted.

During the winter, the poles stay in darkness. This causes carbon dioxide to freeze out of the air. About 25% to 30% of the atmosphere settles onto the poles each year. This adds a layer of dry ice about one meter thick in the north. In the south, the dry ice layer is much thicker at 8 meters. When summer arrives, the sunlight warms the surface. The dry ice then undergoes sublimation, which means it turns directly from a solid into a gas.

Scientists have used many tools to study these icy areas.

For 16 years, researchers tracked changes in the orbits of spacecraft. They found that trillions of tons of gas freeze onto the poles every winter. In 2015, a team used the Very Large Telescope and other observatories. They studied the ratio of different types of water in the atmosphere. They found the ice is eight times richer in deuterium than Earth's oceans. This suggests Mars once had a huge ocean that was 137 meters deep. This ocean might have covered 20% of the planet.

The ice caps also have many interesting shapes and patterns.

Both poles have layers called polar-layered deposits. These layers are made of ice and dust from storms. They are like the rings in a tree that show the past. Sometimes, gas builds up under slabs of dry ice in the south. This pressure causes the ice to rupture and create geyser-like eruptions.

These eruptions carve spider-like patterns into the ground. The gas moves under the ice to reach the surface. This happens very quickly, sometimes in just a few days.

You can think of these layers like a history book of Mars.

Just as ice cores on Earth tell us about old weather, these layers show Martian climate changes. The amount of dust in the layers also matters. Darker dust absorbs more light and causes more melting. The Zhurong rover even found dunes that show how winds changed over time. These winds were likely caused by changes in the planet's tilt. By studying the ice, we learn how the whole world has shifted. This helps us understand how Mars became the dry planet we see today.

Mars features two permanent polar ice caps composed of water ice and dry ice, which is frozen carbon dioxide (CO2). These caps are vital for understanding the history and climate of the Red Planet.

While both poles contain water ice, they differ significantly in size and structure. The northern polar cap is much larger, with a diameter of approximately 1,000 km during the northern summer. It holds about 1.6 million cubic kilometers of ice, which would create a layer 2 km thick if spread evenly.

In contrast, the southern polar cap is smaller, with a diameter of about 350 km and a thickness of 3 km. The total volume of the southern cap and its adjacent layered deposits is also estimated at 1.6 million cubic kilometers.

The seasonal changes on Mars are driven by the planet's axial tilt, which is 25.19 degrees. This tilt is similar to Earth's 23.44-degree tilt and creates distinct seasons.

During the winter, a pole faces continuous darkness. This causes a massive amount of carbon dioxide to freeze out of the atmosphere. Each winter, between 3 trillion and 4 trillion tons of CO2 settle onto the polar caps. This represents about 12 to 16 percent of the entire Martian atmosphere's mass. In the north, this adds a seasonal layer of dry ice about one meter thick. In the south, the seasonal dry ice layer can reach about 8 meters in thickness.

When summer arrives, the sunlight warms the polar regions and triggers sublimation. Sublimation is the process where a substance turns directly from a solid into a gas.

As the dry ice sublimates, it releases large amounts of gas and dust into the atmosphere. This process creates Earth-like frost and large cirrus clouds. In the north, the seasonal dry ice disappears completely each summer, leaving behind the north residual cap. This residual cap is made of water ice and can be as much as three kilometers thick. The northern cap is also warmer and sits at a lower elevation than the southern cap.

The southern polar cap exhibits unique and violent geological activity. During the spring, sunlight warms the subsurface layers beneath the ice. This causes the frozen CO2 to sublime, building up pressure under transparent, one-meter-thick slabs of dry ice. Eventually, the pressure causes the slabs to rupture, resulting in geyser-like eruptions of CO2 gas mixed with dark basaltic sand or dust.

These eruptions are remarkably rapid, occurring within days, weeks, or months. As the gas rushes toward the rupture sites, it carves radial, spider-like channels into the ground.

These features are a striking example of how seasonal atmospheric changes can drive rapid geological transformations on Mars.

Both poles feature polar-layered deposits, which are visible as distinct stripes in the ice. These layers consist of alternating seasonal accumulations of ice and dust from Martian dust storms.

Scientists view these layers much like tree rings or ice cores on Earth. They provide a record of the planet's past climate and atmospheric conditions. The amount of dust in a layer affects its color; darker surfaces absorb more light energy, which can lead to more melting. Researchers use the SHARAD ice-penetrating radar on the Mars Reconnaissance Orbiter to study these layers. This tool allows them to see the contrast in electrical properties between different layers and even find buried craters.

Evidence from the ice caps suggests that Mars was once a much wetter world. By measuring the ratio of deuterium, a heavy isotope of hydrogen, to protium, scientists have studied the history of Martian water. In 2015, researchers found that the polar cap ice is eight times more enriched with deuterium than Earth's oceans. This indicates that Mars has lost a volume of water 6.5 times larger than what is currently stored in its polar caps. This lost water might have once formed a global ocean in the low-lying Vastitas Borealis region. Such an ocean could have covered 20% of the planet and reached depths of nearly a mile.

Changes in the planet's tilt, or obliquity, also influence the size and shape of the ice caps. When the tilt is at its highest, the poles receive more sunlight for longer periods. This extra energy can cause significant melting and the formation of glaciers. The Zhurong rover has provided further clues by finding dunes that suggest the wind patterns changed by about 70 degrees. These shifts in wind direction likely occurred when the planet's tilt changed, marking the end of an ice age. By studying the ice, the dust, and the winds, scientists continue to piece together the complex history of Mars.