Planetary Nomenclature:
A Brief History and Overview

Note from the Editors:  This issue’s lead article is the ninth in a series of reports describing the history and current activities of the planetary research facilities partially funded by NASA and located nationwide. This issue provides a brief history and overview of planetary nomenclature, an important activity that provides structure and coordination to NASA’s planetary exploration program and the scientific analysis of planetary data. — Paul Schenk and Renée Dotson

Humans have been naming the stars and planets for thousands of years, and many of these ancient names are still in use. For example, the Romans named the planet Mars for their god of war, and the satellites Phobos and Deimos, discovered in 1877, were named for the twin sons of Ares, the Greek god of war. In this age of orbiters, rovers, and high-resolution imagery, modern planetary nomenclature is used to uniquely identify a topographical, morphological, or albedo feature on the surface of a planet or satellite so that the feature can be easily located, described, and discussed by scientists and laypeople alike.

History of Planetary Nomenclature

With the invention of the telescope in 1608, astronomers from many countries began studying the Moon and other planetary bodies. Some of these astronomers began to apply names to the features they observed, creating several different systems of nomenclature. Most of these naming systems were applied to the Moon because it was close enough for its surface features to be seen clearly. In particular, Giovanni Riccioli (Italian astronomer, 1598–1671), Johann Schröter (German astronomer, 1745–1816), and Johann Mädler (German astronomer, 1794–1874) created and distributed lunar maps showing three different sets of nomenclature. By the early 1900s, many of the prominent features on the Moon’s nearside were known by at least three different names, leading to the need for a single system of lunar nomenclature.

C:\Users\dotson\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.Word\Figure_1_Riccioli1651MoonMap.jpg

Map of the Moon from G. B. Riccioli’s 1651 Almagestum Novum, showing some of the first lunar nomenclature. Some of these names, such as Mare Frigoris, Mare Serenitatis, and Mare Tranquilitatis, are still in use today.

In 1905, British astronomer Samuel Arthur Saunder (1852–1912) drew the attention of the International Association of Academies to this unsatisfactory state of lunar nomenclature and set in motion the concept of international cooperation in the standardization of lunar nomenclature:

“If a remedy is to be found which will meet with universal assent — and nothing short of this would be a remedy at all — it is obvious that it must be the work of an international committee.” — Monthly Notices of the Royal Astronomical Society, Vol. LXVI, No. 2

In 1907, a Committee on Lunar Nomenclature was established by the Association, and charged with the task of standardizing lunar nomenclature. Saunder enlisted the help of English astronomer Mary Blagg (1858–1944) in the task of preparing a collated list of lunar nomenclature. While a succession of deaths of committee members, including Saunder in 1912, resulted in a final Association report never being published, Blagg’s collated list was published in 1913. This list included multiple discrepancies that the Association needed to resolve. When the International Astronomical Union (IAU) was founded in 1919, one of its first actions was to form a committee to regularize lunar nomenclature. The IAU appointed Blagg and several other astronomers to the newly created nomenclature committee, chaired by H. H. Turner.

The IAU nomenclature committee presented its recommendations in 1932 in the form of the classic publication Named Lunar Formations by Blagg and Müller (published in 1935). The IAU adopted the names included in this publication in 1935. Because this was the first systematic listing of lunar nomenclature, it set the stage for future systems that would be adopted by the IAU for names on other planets and satellites in our solar system.

Later, The System of Lunar Craters, quadrants I, II, III, IV was published by D. W. G. Arthur and others (1963, 1964, 1965, 1966), under the direction of Gerard P. Kuiper. These catalogues listed the names (or other designations) and coordinates of features in the current, greatly expanded lunar nomenclature; the accompanying map (also in four parts) showed their locations. These works were adopted by the IAU and became the recognized sources for lunar nomenclature.

Martian nomenclature was similarly clarified in 1958, when an ad hoc committee of the IAU chaired by Audouin Dollfus recommended for approval the names of 128 albedo features (bright, dark, or colored) observed through groundbased telescopes (IAU, 1960). These names were based on a system of nomenclature developed in the late nineteenth century by the Italian astronomer G. V. Schiaparelli (1879) and expanded in the early twentieth century by E. M. Antoniadi (1929), a Greek-born astronomer working at Meudon, France.

Albedo map of Mars, by Eugène Michel Antoniadi, 1900. Like Riccioli’s lunar map, many of the names on this map are still in use today. Classical albedo names are now used, in conjunction with a descriptor term, to provide new names for morphological features identified by modern planetary scientists in spacecraft images. For example, the albedo name Argyre is used in the IAU-approved feature names Argyre Cavi, Argyre Mons, Argyre Planitia, and Argyre Rupes.

The requirements for extraterrestrial nomenclature were dramatically changed in 1957 when the age of space exploration was inaugurated by the successful flight of Sputnik and by America’s consequent determination to land a man on the Moon in the 1960s. As detailed images became available for one newly discriminated extraterrestrial surface after another, the need to name features on these surfaces became evident. With each Soviet and American mission to the Moon, additional lunar features required names. As a result, the IAU was presented with several problems concerning contested and duplicated names. The international community recognized the need for an objective group to arbitrate and referee the naming process, and the Working Group for Lunar Nomenclature was established by the IAU in 1967 to serve this purpose.

In the mid to late 1960s, planetary scientists were turning their attention to Mars. As the Mariner spacecraft returned photographs of the heavily cratered martian surface, it became apparent that the existing nomenclature for Mars, based on albedo features, was inadequate for the individual topographic features (such as craters, mountains, and valleys) that now needed names. In addition, as was the case for the Moon, several systems of martian nomenclature were in use; the two systems most widely known were developed independently by Schiaparelli and Antoniadi. The IAU was asked to approve one nomenclature system for Mars. In response to this request, a Working Group for Martian Nomenclature was established in 1970, chaired by Gerard de Vaucouleurs. The group was also asked to designate names for the topographic features shown in the new spacecraft images (de Vaucouleurs and others, 1975). At about the same time, Donald H. Menzel chaired an ad hoc lunar committee that suggested names for features discriminated by the Soviet Zond and American Lunar Orbiter and Apollo cameras (IAU, 1971).

The Working Group for Martian Nomenclature presented its recommendations to the IAU at its 1973 meeting in Sydney, Australia, thus setting the stage for a single recognized system of names for Mars. At this same IAU meeting, participants recognized that the nomenclature systems for planets other than the Moon and Mars would benefit from oversight to prevent inconsistencies, contradictions, and application of inappropriate and contentious names. As a result, a new set of nomenclature committees was established to address these solar-system-wide needs. Task Groups comprising an international mix of members were created for the Moon, Venus, Mercury, Mars, and the outer solar system. A Small Bodies Task Group was formed in 1984 to name surface features on small primitive bodies (asteroids and comets).

The Task Groups were formed to conduct the preliminary work of choosing themes and proposing names for features on each newly discriminated planet and satellite. The Working Group for Planetary System Nomenclature (WGPSN), composed mainly of the chairs of the Task Groups, was also formalized at this 1973 meeting. The main functions of the WGPSN were determined to be the oversight and confirmation of the work of the Task Groups, and to set policy. The necessary governing committees were now in place. (See for a list of the current members of the Task Groups and the WGPSN.)

An approval process for naming features was also formalized at the 1973 meeting. New name proposals were first reviewed by the relevant Task Group, and then by the WGPSN. After the WGPSN approved the proposals, names were considered provisionally approved and could be used in publications. Names were fully approved by the IAU at their triennial General Assembly. This approval process is still in use today, except that it has been streamlined. Provisional nomenclature was abolished in 2007, and names are now considered fully approved immediately after WGPSN approval.

In 1982 at Patras, Greece, Harold Masursky of the United States became president of the WGPSN; he was succeeded in 1991 by Kaare Aksnes of Norway, and Kaare was succeeded in 2006 by Rita Schulz of Germany.

As space exploration expanded, so did the database of planetary names. It became apparent that the database needed to reside and be maintained at one location to ensure its accuracy. For many years, Masursky, president of the WGPSN and branch chief for the United States Geological Survey (USGS) Astrogeology Team (now the Astrogeology Science Center), along with his assistant, Mimi Strobell, oversaw the development of the nomenclature database and ensured the correct use of names on maps and in publications. In 1990, after Masursky became ill and could no longer attend to these duties, a meeting was held in Flagstaff during which the new president of the IAU WGPSN and Flagstaff Astrogeology representatives agreed that the maintenance of the nomenclature database should continue in Flagstaff. This decision fosters continuity and accuracy, timely responsiveness to the NASA-funded planetary science community, and the systematic advancement of planetary nomenclature with international cooperation. The IAU agreed to provide approval of names in a timeframe that meets the publication schedules of NASA-funded scientists, while the USGS agreed to adhere to IAU conventions and rules, ensuring that new names will continue to be fair and objective.

C:\Users\dotson\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.Word\Figure_3_28whitaker-obit-1-master768.jpg

Ewen A. Whitaker, left with Gerard P. Kuiper and Raymond Heacock at the University of Arizona’s Lunar and Planetary Laboratory. Whitaker was a British-born astronomer who made enormous contributions to lunar nomenclature and mapping in the Apollo era.

Planetary Nomenclature Today

Today, the six Task Groups and the WGPSN are composed of 38 volunteer members, representing 14countries:  China, Finland, France, Germany, Japan, New Zealand, Norway, Russia, Spain, Switzerland, Vatican City State, Ukraine, the United Kingdom, and the United States. This international composition supports the equitable distribution of names from different ethnic groups, countries, and gender on each planetary body.

There are currently 15,433 IAU-approved surface feature names on 42 planetary bodies, including moons and asteroids. The Gazetteer of Planetary Nomenclature ( contains the database of all names of topographic and albedo features on planets and satellites (and some planetary ring and ring-gap systems) that the IAU has named and approved from its founding in 1919 through the present time.

The Gazetteer of Planetary Nomenclature database and website are maintained by the database manager at the USGS Astrogeology Science Center in Flagstaff. The database manager responds to requests from researchers for new names through the Gazetteer website, and works with researchers to refine and create their name proposals, including images and database information. The database manager tracks proposals through the IAU approval system, working with Task Group chairs and the WGPSN chair to move proposals through the system in a timely manner.

How Names Are Approved

Planetary nomenclature, like terrestrial nomenclature, is used to uniquely identify a topographical, morphological, or albedo feature — not geological features or units — on the surface of a planet or satellite, so that the feature can be easily located, described, and discussed. A distinction is made between topographical, morphological, or albedo features and geological features to avoid assigning names based on scientific interpretations, which may change over time.

When the first images of the surface of a planet or satellite are obtained, themes for naming features are chosen and names of a few important features are proposed, usually by the appropriate IAU Task Group. Recent NASA mission teams have worked with the appropriate Task Group to establish themes and compile name banks. Later, as higher-resolution images and maps become available, names for additional features may be requested by investigators mapping or describing specific surfaces or topographic formations.

Planetary scientists preparing manuscripts for peer-reviewed journal articles or maps (or students, with a letter of support from the advisor) may request a planetary feature be named. Features are named only when they have special scientific interest, and when the naming of such features is useful to the scientific and cartographic communities at large. Requestors submit a short justification describing why the feature needs to be named, and a timeline for publication of the work in which the name will appear. Also required are images of the feature, along with basic data about the feature (location, size, etc.). Name suggestions for specific features, submitted during the proposal process, will be considered, but final selection of the names is the responsibility of the IAU.

Image result for planetary nomenclature

The Gazetteer of Planetary Nomenclature can help identify a feature on the surface of a planet or satellite so that the feature can be easily located, described, and discussed. The Gazetteer contains detailed information about all names of topographic and albedo features on planets and satellites (and some planetary ring and ring-gap systems) that the IAU has named and approved from its founding in 1919 through the present time.

The request is reviewed by the appropriate Task Group. Names approved by a Task Group are then submitted by the Task Group chair to the WGPSN. Upon successful review by vote of the members of the WGPSN, names are considered approved as official IAU nomenclature, and can be used on maps and in publications. Approved names are immediately entered into the Gazetteer of Planetary Nomenclature, and posted on its website.

The WGPSN and Task Groups follow certain established rules and conventions when approving names:

  • Nomenclature is a tool and the first consideration should be to make it simple, clear, and unambiguous.
  • Where appropriate, the WGPSN strongly supports an equitable selection of names from ethnic groups, countries, and gender on each map; however, a higher percentage of names from the country planning a landing is allowed on landing site maps.
  • Duplication of the same surface feature name on two or more bodies, and of the same name for satellites and minor planets, is discouraged.
  • No names having political, military, or religious significance may be used, except for names of political figures prior to the nineteenth century.
  • Commemoration of persons on planetary bodies should not normally be a goal in itself, but may be employed in special circumstances and is reserved for persons of high and enduring international standing. Persons being so honored must have been deceased for at least three years.
  • Names for all planetary features include a descriptor term, with a few exceptions. For craters, the descriptor term is implicit. Names and their descriptor terms are based solely on the morphology (shape) of a feature, and explicitly do not indicate geological origin.
  • Additional rules and conventions are added as the IAU formulates an interesting and meaningful nomenclature for individual planetary bodies.

Descriptor Terms and Naming Categories (Themes)

The Gazetteer lists 56 descriptor terms, or feature types, that are used to describe named planetary features. Determining the most appropriate descriptor is one of the critical initial steps in the naming process, and is usually, but not always, straightforward. For example, the descriptors vallis (valley, canyon-like, often sinuous trough) and fossa (long, narrow depression; ditch; narrow, linear trench) may seem distinct, and most morphological features fit one description or the other very neatly, but some individual features may have characteristics of both descriptors. Nature does not always produce features that fit tidily into our little boxes!

Many feature types are common to several planetary bodies (such as crater or mons), and some are applied only on single bodies. For example, a flumen (plural flumina) is a channel on Titan that may carry liquid.

Once the feature has been assigned a descriptor, a name is chosen that fits the naming category (theme) assigned to that descriptor. Naming categories allow for a large number of potential names to be in reserve for future name requests. For example, small (60 kilometers or smaller) craters on Mars are named for small towns and villages of the world — no commemoration of specific modern towns or villages is intended; this category is simply a large source of international names. Likewise, craters on Mercury are named for deceased artists, musicians, painters, and authors who have made outstanding or fundamental contributions to their field, and have been recognized as historically significant figures for more than 50 years.

In Conclusion

The IAU’s WGPSN, and its Task Groups, has worked for almost a century to build and maintain a clear, simple, unambiguous system of nomenclature for our solar system. This nomenclature system aims to preserve many of the naming themes used by early astronomers, while adapting to the needs of modern planetary science and space missions. We look forward to upcoming missions that will provide high-resolution imagery of Jupiter’s icy moons Ganymede, Callisto, and Europa (the JUICE and Europa Clipper missions, set to launch in 2022) and as-yet unexplored planetary bodies, such as the Lucy mission to explore six Jupiter Trojan asteroids (launch date in October 2021) and the metallic asteroid Psyche (launch date in October 2023).

About the Authors

C:\Users\dotson\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.Word\Gaither_bio_pic_LPI_2.jpg Tenielle Gaither is a geologist at the USGS Astrogeology Science Center in Flagstaff, Arizona. She is the assistant database manager for the Gazetteer of Planetary Nomenclature and project chief for the Astrogeology Geologic Materials Collection. She received an M.S. in Geology in 2011 from Northern Arizona University for her research on silicic magma geochemistry. Gaither joined USGS Astrogeology in 2010, and works on a variety of projects including impact crater studies, planetary geologic mapping, and education and public outreach.


C:\Users\dotson\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.Word\rhayward_photo.jpg Rosalyn Hayward is a geologist at the USGS Astrogeology Science Center in Flagstaff, Arizona. She is the Project Chief for the Nomenclature project and the database manager for the Gazetteer of Planetary Nomenclature, helping researchers to navigate the IAU name-approval process. Hayward is also PI for a Mars analog project doing dune field research on the Navajo Nation, near Grand Falls, Arizona. Her research interests include planetary aeolian processes and she has been active in the series of International Planetary Dune Workshops that began in 2008.