Polar ice cap

Polar ice cap

Overview

A polar ice cap is a high latitude region of a planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...

 or natural satellite
Natural satellite
A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets....

 that is covered in ice
Ice
Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...

. There are no requirements with respect to size or composition for a body of ice to be termed a polar ice cap, nor any geological requirement for it to be over land; only that it must be a body of solid phase matter in the polar region
Polar region
Earth's polar regions are the areas of the globe surrounding the poles also known as frigid zones. The North Pole and South Pole being the centers, these regions are dominated by the polar ice caps, resting respectively on the Arctic Ocean and the continent of Antarctica...

. This causes the term 'polar ice cap' to be something of a misnomer, as the term ice cap
Ice cap
An ice cap is an ice mass that covers less than 50 000 km² of land area . Masses of ice covering more than 50 000 km² are termed an ice sheet....

 itself is applied with greater scrutiny as such bodies must be found over land, and possess a surface area of less than 50,000 km²: larger bodies are referred to as ice sheets.

The composition of the ice will vary.
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Encyclopedia

A polar ice cap is a high latitude region of a planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...

 or natural satellite
Natural satellite
A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets....

 that is covered in ice
Ice
Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...

. There are no requirements with respect to size or composition for a body of ice to be termed a polar ice cap, nor any geological requirement for it to be over land; only that it must be a body of solid phase matter in the polar region
Polar region
Earth's polar regions are the areas of the globe surrounding the poles also known as frigid zones. The North Pole and South Pole being the centers, these regions are dominated by the polar ice caps, resting respectively on the Arctic Ocean and the continent of Antarctica...

. This causes the term 'polar ice cap' to be something of a misnomer, as the term ice cap
Ice cap
An ice cap is an ice mass that covers less than 50 000 km² of land area . Masses of ice covering more than 50 000 km² are termed an ice sheet....

 itself is applied with greater scrutiny as such bodies must be found over land, and possess a surface area of less than 50,000 km²: larger bodies are referred to as ice sheets.

The composition of the ice will vary. For example Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

's polar ice caps are mainly water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 ice, while Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...

's polar ice caps are a mixture of solid phase carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 and water ice.

Polar ice caps form because high latitude regions receive less energy in the form of solar radiation from the sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

 than equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

ial regions, resulting in lower surface temperatures.

The Earth's polar ice caps have changed dramatically over the last 12,000 years.
Season
Season
A season is a division of the year, marked by changes in weather, ecology, and hours of daylight.Seasons result from the yearly revolution of the Earth around the Sun and the tilt of the Earth's axis relative to the plane of revolution...

al variations of the ice caps takes place due to varied solar energy absorption as the planet or moon revolves around the sun. Additionally, in geologic time scales, the ice caps may grow or shrink due to climate
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...

 variation. Ice caps are generally in the negative in temperature.

North Pole



Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

's north pole
North Pole
The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is, subject to the caveats explained below, defined as the point in the northern hemisphere where the Earth's axis of rotation meets its surface...

 is covered by floating pack ice (sea ice
Sea ice
Sea ice is largely formed from seawater that freezes. Because the oceans consist of saltwater, this occurs below the freezing point of pure water, at about -1.8 °C ....

) over the Arctic Ocean
Arctic Ocean
The Arctic Ocean, located in the Northern Hemisphere and mostly in the Arctic north polar region, is the smallest and shallowest of the world's five major oceanic divisions...

. Portions of the ice that don't melt seasonally can get very thick, up to 3–4 meters thick over large areas, with ridges up to 20 meters thick. One-year ice is usually about a meter thick. The area covered by sea ice ranges between 9 and 12 million km². In addition, the Greenland ice sheet
Greenland ice sheet
The Greenland ice sheet is a vast body of ice covering , roughly 80% of the surface of Greenland. It is the second largest ice body in the world, after the Antarctic Ice Sheet. The ice sheet is almost long in a north-south direction, and its greatest width is at a latitude of 77°N, near its...

 covers about 1.71 million km² and contains about 2.6 million km³ of ice.

According to the National Snow and Ice Data Center
National Snow and Ice Data Center
The National Snow and Ice Data Center, or NSIDC, is a United States information and referral center in support of polar and cryospheric research...

, "since 1979, winter Arctic ice extent has decreased about 4.2 percent per decade." Both 2008 and 2009 had a minimum Arctic sea ice extent somewhat above that of 2007. At other times of the year the ice extent is still sometimes near the 1979-2000 average, as in April 2010, by the data from the National Snow and Ice Data Center
National Snow and Ice Data Center
The National Snow and Ice Data Center, or NSIDC, is a United States information and referral center in support of polar and cryospheric research...

.

South Pole



The land mass of the Earth's south pole
South Pole
The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is one of the two points where the Earth's axis of rotation intersects its surface. It is the southernmost point on the surface of the Earth and lies on the opposite side of the Earth from the North Pole...

, in Antarctica, is covered by the Antarctic ice sheet
Antarctic ice sheet
The Antarctic ice sheet is one of the two polar ice caps of the Earth. It covers about 98% of the Antarctic continent and is the largest single mass of ice on Earth. It covers an area of almost 14 million square km and contains 30 million cubic km of ice...

. It covers an area of about 14.6million km² and contains 25-30 million km³ of ice. Around 70% of the fresh water
Fresh Water
Fresh Water is the debut album by Australian rock and blues singer Alison McCallum, released in 1972. Rare for an Australian artist at the time, it came in a gatefold sleeve...

 on the Earth is held in this ice sheet. See Climate of Antarctica
Climate of Antarctica
The climate of Antarctica is the coldest on the whole of Earth. Antarctica has the lowest naturally occurring temperature ever recorded on the ground on Earth: −89.2 °C at Vostok Station. It is also extremely dry , averaging 166 mm of precipitation per year...

.

Data from the National Snow and Ice Data Center
National Snow and Ice Data Center
The National Snow and Ice Data Center, or NSIDC, is a United States information and referral center in support of polar and cryospheric research...

 shows that the sea ice coverage of Antarctica has a slightly positive trend over the last three decades (1979–2009).

Mars




The planet Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...

 also has polar ice caps, but they consist of frozen carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 as well as water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

. The ice caps change with the Martian seasons-the carbon dioxide ice sublimes
Sublimation (physics)
Sublimation is the process of transition of a substance from the solid phase to the gas phase without passing through an intermediate liquid phase...

 in summer, uncovering a surface of layered rocks, and then reforms in winter.

Data collected in 2005 from NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

missions to Mars show that the carbon dioxide "ice caps" are melting to reveal the majority of the cap is water ice. The most widely accepted explanation is that fluctuations in the planet's orbit are causing the changes.