Tholus

In planetary nomenclature, a tholus /ˈθoʊləs/ (pl. tholi /ˈθoʊlaɪ/) is a small domical mountain or hill.[1][2] The word is from the Greek θόλος, tholos (pl. tholoi),[3] which means a circular building with a conical or vaulted roof.[4] The Romans transliterated the word into the Latin tholus, which means cupola or dome.[5] In 1973, the International Astronomical Union (IAU) adopted tholus as one of a number of official descriptor terms for topographic features on Mars and other planets and satellites.[6][7] One justification for using neutral Latin or Greek descriptors was that it allowed features to be named and described before their geology or geomorphology could be determined.[8] For example, many tholi appear to be volcanic in origin, but the term does not imply a specific geologic origin.[9] Currently (March 2015), the IAU recognizes 56 descriptor terms.[1] (See Planetary nomenclature.) Tholi are present on Venus, Mars, asteroid 4 Vesta, dwarf planet Ceres, and on Jupiter's moon Io.

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  Map of the Tharsis quadrangle showing major features, several of which are tholi. Tharsis contains many volcanoes, including Olympus Mons, the tallest known volcano in the Solar System.
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  2001 Mars Odyssey THEMIS mosaic of Ceraunius Tholus (lower volcano) and Uranius Tholus (upper volcano). Ceraunius Tholus is about as high as Earth's Mount Everest.
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  Western part of Jovis Tholus, as seen by THEMIS on Mars Odyssey spacecraft. Jovis Tholus is in the Tharsis quadrangle.