Exoplanets, celestial bodies orbiting stars beyond our solar system, represent a vast and diverse population of worlds. With thousands confirmed and countless more awaiting discovery, a standardized approach to identifying them is necessary for astronomers worldwide. This systematic method prevents confusion and allows for efficient cataloging and communication within the scientific community.
Standard Scientific Designations
The primary method for naming exoplanets involves a systematic extension of the convention used for multiple-star systems. An exoplanet’s designation typically begins with the name of its parent star, followed by a lowercase letter. The first planet discovered in a system receives the designation ‘b’, the second ‘c’, the third ‘d’, and so on, regardless of its orbital distance from the star. If multiple planets are discovered simultaneously, the one closest to the star is designated ‘b’, with subsequent letters assigned to planets farther out.
The parent star itself often derives its name from established astronomical catalogs or specific survey projects. For instance, stars from the Henry Draper (HD) Catalogue or projects like Kepler and TESS contribute the initial part of an exoplanet’s name. An example is HD 209458 b, where “HD 209458” identifies the star from the Henry Draper Catalogue, and “b” indicates it was the first planet found orbiting that particular star. Similarly, Kepler-186f refers to the sixth planet discovered around the 186th star identified by the Kepler space telescope, and WASP-12b is the first planet found by the Wide Angle Search for Planets (WASP) project around its twelfth identified star.
The Role of the International Astronomical Union (IAU)
The International Astronomical Union (IAU) serves as the globally recognized authority for assigning official designations to all celestial objects, including exoplanets and their host stars. This organization is responsible for establishing and maintaining the guidelines for exoplanet nomenclature, ensuring consistency across the scientific community. The IAU’s Working Group on Exoplanet Names, among other committees, plays a significant role in this process.
While astronomers typically assign the initial provisional scientific designations upon discovery, the IAU formalizes and approves these names. This oversight prevents duplication and maintains a cohesive system for tracking the thousands of known exoplanets. The IAU’s involvement ensures that the nomenclature remains standardized and accessible for researchers worldwide.
Public Naming Campaigns and Historical Context
Beyond the formal scientific designations, the IAU has introduced initiatives allowing public participation in naming a select few exoplanets and their host stars. These “NameExoWorlds” campaigns offer unique opportunities for the public to propose proper names, which then supplement the standard alphanumeric designations. Such campaigns are infrequent and do not replace the scientific naming system, but rather add more memorable and culturally significant names to specific systems.
For example, the IAU launched its first NameExoWorlds contest, followed by the IAU100 NameExoWorlds project, which allowed countries worldwide to name a planetary system. These public names often follow specific rules, such as being pronounceable, non-offensive, and not subject to copyright. The naming of 51 Pegasi b, the first exoplanet discovered around a Sun-like star in 1995, holds historical significance. While its official designation followed the star-plus-letter format that became standard, it was later given the proper name “Dimidium” through a public campaign, reflecting its status as a pioneering discovery that set a precedent for future exoplanet nomenclature.