planetary features

Planetary nomenclature is handled by the International Astronomical Union (IAU) according to a set procedure and rules. When images are first obtained of the surface of a planet or moon, a theme for naming features is chosen and a few important features are labeled, usually by members of the appropriate IAU task group. Later, as higher resolution images and maps become available, suggested names for additional features go to the task group and, if successfully reviewed, are submitted to the IAU Working Group for Planetary System Nomenclature (WGPSN). Upon successful review by the members of the WGPSN, names are considered provisionally approved and can be used on maps and in publications as long as the provisional status is clearly stated. Provisional names only become official if they are approved by the IAU's General Assembly, which meets triennially. Names for most planetary features include a term that describes the type of feature; for example, Ithaca Chasma (on Saturn's moon Tethys).


Types of planetary feature
feature description example
catena A crater chain or line of (usually overlapping) craters Gipul Catena, Callisto
chasma A steep-walled trough or large canyon Diana Chasma, Venus
dorsum A meandering, elongated elevation or ridge, also known as a wrinkle ridge Antoniadi Dorsum, Mercury
farrum A pancake-like feature when see from above. Applied especially to flat-topped volcanoes on Venus Aegina Farrum, Venus
fluctus Terrain resulted from the flow of molten material Tung Yo Fluctus, Io
fossa A long, straight, narrow depression (literally, 'ditch') Isbanir Fossa, Enceladus
labes A landslide or structure caused by a landslide Candor Labes, Mars
labyrinthus An intersecting valley complex Noctis Labyrinthus, Mars
lacus A small plain (literally, lake') Lacus Somniorum, Moon
macula A dark round or irregular spot Tyre Macula, Europa
mare A lava-flooded impact basin on the Moon Mare Tranquilitatis
mensa A small flat-topped prominence with cliff-like edges Cydonia Mensa, Mars
mons A mountain or volcano Maxwell Montes, Venus
palus A small plain (literally, 'swamp') Palus Somnii, Moon
patera A shallow crater with a scalloped or complex edge Orcus Patera, Mars
planitia A broad low-lying plain Borealis Planitia, Mercury
planum A large plateau or smooth high plain Lakshmi Planum, Venus
regio A large area marked by reflectivity or color distinctions from adjacent areas, or a broad geographic region Beta Regio, Venus
rupes A scarp or line of cliffs produced by faulting or erosion Rupes Recta, Moon
scopulus An irregular, degraded scarp Eridana Scopulus, Mars
sinus An indentation at the edge of high ground (literally, 'bay') Sinus Iridum, Moon
sulcus An intricate network of linear furrows and ridges Kishar Sulcus, Ganymede
terra A large highland region Roncevaux Terra, Iapetus
tessera Polygonally patterned, tile-like terrain Fortuna Tessera, Venus
tholus A small dome-shaped mountain or hill Apis Tholus, Io
vallis A sinuous channel, often with tributaries Valles Marineris, Mars
vastitas A widespread lowland plain Vastitas Borealis, Mars


See also:

impact feature
multiringed basin
rift valley
shatter cone
shield volcano