The locking of the rotation of a body to its revolution around another body through gravitational forcing. (also known as spin orbit lock)
The dividing line between daylight and darkness on a planet or a moon.
The edge of the apparent disk of a body, as in "the limb of the moon."
The lunar lowlands filled by successive flows of dark lava; from the Latin word for sea. (singular "mare").
A narrow, winding valley on the moon caused by ancient lava flows along narrow channels.
Pulverized rock scattered by meteorite impacts on a planetary surface.
Ejecta from a meteorite impact, forming white streamers radiating from some lunar craters.
A crater formed by the impact of debris ejected from a larger crater.
Very large impact basin in which there are concentric rings of mountains.
Meteorite of microscopic size. These meteorites are especially important for airless worlds as they produce regolith (ex: the moon).
The age of a geological feature referred to other features. For example, relative ages reveal that the lunar maria are younger than the highlands.
An age determined in years, as from radioactive dating.
A porous rock formed by solidified lava with trapped bubbles.
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.
A rock composed of fragments of earlier rocks bonded together.
Dirt made up from crushed rock fragments.
Strangely disturbed regions of the moon opposite the locations of the Imbrium Basin and Mare Orientale.
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.
The coincidental agreement between two periodic phenomena; commonly applied to agreements between orbital periods, which can make orbits more stable or less stable.
A curved cliff such as those found on Mercury.
The relatively smooth terrain on Mercury.
Apparently young plain on Mercury formed by lava flows at or soon after the formation of the Caloris Basin.