Geology. the icecap situated at either end of the earth's poles.
Astronomy. either of the two bright areas around the poles of the planet Mars, consisting of water ice and frozen carbon dioxide.
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Origin of polar cap
First recorded in 1890–95
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Science definitions for polar cap
The mass of ice that covers either of the Earth's polar regions year-round.
The mass of frozen carbon dioxide and water that covers either of Mars's polar regions.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.