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Used by planetary scientists to refer to water, methane, and ammonia which usually occur as solids in the outer solar system. This is why when scientists find ice on Mars they refer to is was 'water ice.'

ice as rock

Water-ice (frozen H20) is an important geologic material on many of the outer planet satellites. Under various conditions ice can have viscosities and flow properties similar to different types of molten rock (basaltic - rhyolitic), and therefore may also result in the formation of similar geologic structures.

ice volcanism

The eruption of molten ice or gas-driven solid fragments onto the surface of a planetary body.

ice-volcanic melt

The semi-fluid or fluid material associated with ice volcanism, and like molten rock, can have a wide variety of viscosities and other flow properties.

impact crater

A crater formed on a surface by the collision of a projectile.


An object which strikes the surface of a celestial body.


The inclination of a planet's orbit is the angle between the plane of its orbit and the ecliptic; the inclination of a moon's orbit is the angle between the plane of its orbit and the plane of its primary's equator.

inferior planets

The planets Mercury and Venus are called inferior planets because their orbits are closer to the Sun than is Earth's orbit. (The other planets are called "superior planets.)


Light that is so red humans cannot see it. A band of the electromagnetic spectrum between the visible and the microwave. Photons of infrared light are less energetic than photons of visible light.

interplanetary magnetic field (IMF)

The magnetic field carried with the solar wind.


A region of charged particles in a planet's upper atmosphere; the part of the Earth's atmosphere beginning at an altitude of about 25 miles and extending outward 250 miles or more.

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Last Updated: 25 Oct 2013