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Is water locked in polar caps?

The Ice on Mars Shrinks and Grows


NASA image of Mars with prominent surface features called out
Polar ice caps are among the prominent surface features of Mars
NASA illustration
A century ago, astronomers became intrigued by Mars' regularly-changing polar caps, dust storms and surface markings. Those changes were attributed to the planet's inclined axis, which gave it seasons. In fact, they thought the seasonal Mars looked so much like Earth that it might be inhabited.

Today, we don't see any native martians, but there is evidence that water on Mars may be locked in polar ice caps buried under the two large carbon dioxide frost caps.

The NASA orbiter 2001 Mars Odyssey, searching for water ice beneath the surface, reported that in the regions of the planet north and south of 60 degrees latitude, the surface is well over 50 percent water ice by volume.

If it were to melt, along with some water frozen in the Martian soil, the liquid water might be enough to form an ocean several miles deep on the low-lying northern hemisphere.

Or, as one scientist put it, "If just the top meter of ice deposits around the martian north pole were melted, there would be enough liquid water to fill Lake Michigan."

Seasonal changes. The planet's rotation axis is tilted with respect to the orbital plane by almost 24 degrees, so Mars does experience significant seasonal differences in the amount of sunlight falling on a hemisphere during a year.

The difference between winter and summer is more extreme on Mars than on Earth, due to the greater eccentricity of the Martian orbit.

The Red Planet receives 40 percent more sunlight during its southern summer, when nearest the Sun, than during its southern winter, when the Sun is most distant. That makes for relatively hot southern summers and mild northern winters, but cool northern summers and cold southern winters.

Polar regions. The regions around the planet's north pole and south pole show evidence of the martian climate change. The pattern suggests varying amounts of dust and ice were deposited over long time spans in response to slow changes in the polar climate.

How cold is it? Mars has a very thin atmosphere, mostly carbon dioxide. The surface temperature varies from –194° to 80° Fahrenheit.

Ice. Ice usually is water frozen to a solid state when its temperature drops to or below 32° Fahrenheit or 0° Celsius. Water expands when it freezes.

Planetary scientists use the word ice to refer to water, methane, and ammonia when they occur as solids.

Frost. Frost is a covering of ice crystals that are deposited on the ground or on an exposed surface when water vapor in the atmosphere condenses as the air temperature reaches down to or is below 32° Fahrenheit or 0° Celsius.

Ice cap. An ice cap is a mass of ice covering a large area of land. For instance, polar regions of a planet. The area of ice is smaller than what might be called an ice sheet.

The land around Mars' north and south poles – the polar terrain – is covered with frost caps over top of ice caps. Some of the frost caps are frozen carbon dioxide. Dust in the cap makes the ice look reddish.

Melt-and-freeze cycle. Astronomers have watched the annual shrinkage and expansion of Mars' polar caps for the past two centuries.

The caps on Mars expand outward from the poles to cover up to 30 percent of the planet's surface area during the martian winter, but shrink to smaller caps covering only one percent of the planet's surface in summer.

Snow. Scientists now suspect that during some past climate eons ago there was enough moisture in the martian atmosphere that snow actually fell on the surface. If so, it probably was mixed with a small amount of wind-blown dust.

Ice flows. It is not known whether the ice on Mars flows. There is no evidence for glacial erosion on Mars.

Is there water today? We don't know how much water there is today on Mars. The nearest thing on Earth to the dry martian landscapes are the cold, dry valleys of Antarctica. There is seasonal frost in those Antarctic valleys.

Clouds and fog. Although there is not much water, it still can condense out of the atmosphere forming clouds high in the atmosphere. There are fogs in valleys, and thin layers of frost in winter.

A long time ago. There is evidence of water and water ice in the deep past.

Patterns on the northern plains suggest there may have been a cycle of freezing and thawing with widespread creeping of frost in the past when average temperatures were higher and there was more surface water.

Water features. The planet displays many physical features that on Earth would be explained either by heavy floods or by the slow movement of groundwater. Without water, you would not expect to see features, such as outflow channels and valley networks, that look like rivers and floods carved them. However, they seem to be almost everywhere on Mars. Of course, younger and older are relative terms when we say outflow channels seem younger than valley networks. Both are very old.

How old is it? Scientists date the surfaces of Mars by their records of cratering. That makes it difficult to determine the ages of things after the period of heavy bombardment that created most of the craters on Mars 3.8 billion years ago and earlier.

The uplands of Mars are saturated with craters. Scientists think the Martian surface is extremely ancient.

Floods. Where could floods come from? There might not be much living in the ground on Mars. The soil sterilizes itself because it is so dry, its chemistry is oxidizing, and ultraviolet (UV) radiation kills organisms that may try to grow there.

Learn more:
Human Exploration of Mars:
There have been three stages of exploration so far
Sand dunes: Dust Storms: Air: Carbon Dioxide: Outflow Channels: Valley Networks: Rift Valley: Ice: Ice caps: Frost: Water: Artesian Water: Mars Weather: Mars Photo Galleries: Planet features: Canals: Rocks: Mountains: Dating and aging: Seasons:
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Artist conception of Mars with water four billion years ago
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