Albedo the relative amount of sunlight reflected by a planetary surface. Low-albedo objects are dark and absorb most incident sunlight.

Anti-Jovian hemisphere the side of a satellite always facing away from Jupiter (see Synchronous rotation).

Apex (and antapex) the point (or region) on a planet or satellite that is most forward as it orbits (usually centered at 0°N, 90°W).

Basalt a common silicate volcanic rock formed from cooled lavas. Lower in silica than granite, basalts tend to be enriched in magnesium, iron and calcium, and include minerals such as pyroxene, olivine and plagioclase.

Breccia a rock formed during impact or volcanic eruption consisting of broken fragments of older rocks and refrozen melt, reaggregated to form a new unit of rock.

Caldera a circular, oval, or polygonal volcanic depression formed by collapse due to eruption. Often forms a walled depression, which can sometimes be filled by lava or lava flows.

Catena see Crater chain.

Central dome a mound of fractured deep-crustal material in the center of a crater uplifted during the impact event. This distinct variation on icy satellites takes the form of a broad rounded mound in larger craters.

Central peak a mound of fractured deep-crustal material in the center of a crater uplifted during the impact event. Usually takes form of conical peak(s).

Chaos a region of disrupted crust on Europa, often formed from fragmented remnants of the original crust as well as new material.

Comet a small (<100 km across) irregularly shaped object orbiting the Sun, usually at great distances, and composed of ices, organic (carbon-rich) materials, and silicates.