Astro- Ch. 21 The Moon and Mercury: Comparing Airless Worlds

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Manheim Township Astronomy: The Solar System and The Universe

tidally coupled

The locking of the rotation of a body to its revolution around another body through gravitational forcing. (also known as spin orbit lock)

terminator

The dividing line between daylight and darkness on a planet or a moon.

limb

The edge of the apparent disk of a body, as in "the limb of the moon."

maria

The lunar lowlands filled by successive flows of dark lava; from the Latin word for sea. (singular "mare").

sinuous rille

A narrow, winding valley on the moon caused by ancient lava flows along narrow channels.

ejecta

Pulverized rock scattered by meteorite impacts on a planetary surface.

rays

Ejecta from a meteorite impact, forming white streamers radiating from some lunar craters.

secondary crater

A crater formed by the impact of debris ejected from a larger crater.

multiringed basins

Very large impact basin in which there are concentric rings of mountains.

micrometeorites

Meteorite of microscopic size. These meteorites are especially important for airless worlds as they produce regolith (ex: the moon).

relative age

The age of a geological feature referred to other features. For example, relative ages reveal that the lunar maria are younger than the highlands.

absolute ages

An age determined in years, as from radioactive dating.

vesicular basalt

A porous rock formed by solidified lava with trapped bubbles.

anorthosite

Rock of aluminum and calcium silicates found in the lunar highlands. Also known as the genesis rock, the oldest known rock in the solar system at 4.1 billion years old.

breccia

A rock composed of fragments of earlier rocks bonded together.

regolith

Dirt made up from crushed rock fragments.

jumbled terrain

Strangely disturbed regions of the moon opposite the locations of the Imbrium Basin and Mare Orientale.

capture hypothesis

The theory that the moon formed elsewhere in the solar system and was later captured by Earth.

large impact theory

The theory that the moon formed from debris ejected during a collision between earth and a large planetesimal.

resonance

The coincidental agreement between two periodic phenomena; commonly applied to agreements between orbital periods, which can make orbits more stable or less stable.

lobate scarps

A curved cliff such as those found on Mercury.

intercrater plains

The relatively smooth terrain on Mercury.

smooth plains

Apparently young plain on Mercury formed by lava flows at or soon after the formation of the Caloris Basin.

Flickr Creative Commons Images

Some images used in this set are licensed under the Creative Commons through Flickr.com. Click to see the original works with their full license.

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