Naming of exoplanets 

The IAU fully supports the involvement of the general public in the naming of astronomical objects, whether directly or through an independent organised vote, in the naming of planetary satellites, newly discovered exoplanets, and their host stars. This follows a well-established tradition for naming Solar System objects.

The IAU does not consider itself as having a monopoly on the naming of celestial objects — anyone can in theory adopt names the way they choose. However, given the publicity and emotional investment associated with these discoveries, worldwide recognition is important and the IAU offers its unique experience for the benefit of a successful public naming process (which must remain distinct, as in the past, from the scientific designation issues)

The process for naming exoplanets is organised by the IAU Executive Committee Working Group Public Naming of Planets and Planetary Satellites.

Scientific designations

The scientific nomenclature for the designations of exoplanets usually consists of two elements: 1) a proper noun or abbreviation, sometimes with associated numbers 2) followed by a lowercase letter.

The first element can derive from a number of sources. A common source is an exoplanet's host star's widely recognized, common or astronomical catalogue name. Alternatively, exoplanets are often named after the scientific instrument or project that discovered the exoplanet.

We'll look at several examples of the first element of exoplanetary naming. 51 Pegasi b, for instance, is an exoplanet around the star 51 Pegasi in the constellation Pegasus. The star received this particular catalogue designation by English astronomer John Flamsteed in his 1712 star atlas. Another common star catalogue used for exoplanet names is GJ, from a 1970 expansion of German astronomer Wilhelm Gliese's 1957 index. (A handful of Gliese exoplanets also exist as well.) An example world with this naming is GJ 1214 b, meaning it is the 1,214th entry in the star catalogue. Still other examples include the HD and HIP exoplanets. An example of an exoplanet named after its star's common name is Fomalhaut b, derived from an Arabic name originally used at least 2,000 years ago.

Exoplanets that are named after their discovering instrument include the Kepler planets, for the National Aeronautical and Space Administration's (NASA) Kepler space telescope. Another instance is the CoRoT planets, for the French Space Agency's (CNES) and the European Space Agency's (ESA) spacecraft, COnvection ROtation and planetary Transits. Example planets are Kepler-186 f and CoRoT-7b, respectively. The number in each name refers to the order of the exo-solar system's detection or identification in the instrument's data.

Exoplanets that are named after astronomical or planet-searching projects include the HAT planets, via the Hungarian Automated Telescope Network (HATNet), and the WASP planets, from the SuperWASP project, both of which are ground-based efforts. Numerous other examples exist. The nation of Qatar funds an exoplanet-hunting project, and its planets follow the naming scheme of Qatar-1b, and so on. The MOA and OGLE exoplanets were discovered through a particular observation technique, called gravitational microlensing, by the Microlensing Observations in Astrophysics (MOA) and the Optical Gravitational Lensing Experiment (OGLE) projects, respectively.

We'll now address the second letter element appearing in exoplanet scientific designations. Unlike the proper noun, the letter term applies universally in almost all nomenclature styles. The letter indicates the order of the planet's discovery around its host star. The first exoplanet discovered in another solar system is designated b; the second, c; the third d; and so on. The letter does not indicate the planet’s orbital placement around its host star, so Exoplanet-c can be closer to, or farther away from, the star that it co-orbits with Exoplanet-b.

The lowercase lettering style is drawn from the IAU-established rules for naming binary and multiple star systems. A primary star, which is brighter and typically bigger than its secondary or tertiary companion stars, is designated by a capitalized A. Its companions are labelled B and C, and so on. Sirius, the brightest star in the sky, demonstrates this nomenclature. Actually a double star, the bright star we see in Canis Major is Sirius A, and its dim companion is Sirius B. The first exoplanet tentatively identified around the second brightest star in the triple star system, Alpha Centauri, is accordingly called Alpha Centauri Bb. If an exoplanet orbits both of the stars in a binary system, its name can be, for example, Kepler-34(AB) b.

Public naming campaigns

In order to assist in the selection process while avoiding mistakes due to incomplete information, the IAU asks organizations planning to issue a public naming campaign to do so in association with the IAU, and inform its General Secretary of their intentions and proposals. The IAU is ready to assist in resolving problems and providing relevant information. More precisely, the IAU will welcome proposals from organizations, provided the following rules are followed:

  1. Prior to any public naming initiative, often a vote (hereafter "the process”), the IAU should be contacted from the start by a Letter of Intent sent to the IAU General Secretary by an organization. Scientists or science communicators may be involved in the process;

  2. The organization should list its legal or official representatives and its goals, and explain the reasons for initiating the process for naming a particular object or set of objects;

  3. The process should not involve any financial payment between any parties, for any purpose;

  4. The process must guarantee a wide international participation;

  5. The public names proposed in naming campaign should follow the naming rules and restrictions adopted for Minor Bodies of the Solar System, by the IAU and by the Minor Planet Center (see http://www.iau.org/public/naming/#minorplanets, or, for more details, http://www.minorplanetcenter.net/iau/info/Astrometry.html#nametype).
    In particular:

    Proposed names should be:

    • 16 characters or less in length;
    • Preferably one word;
    • Pronounceable (in some language);
    • Non-offensive;
    • Not too similar to an existing name of an astronomical object. Names already assigned to astronomical objects can be checked using the links http://cds.u-strasbg.fr/cgi-bin/sesame (for galactic and extragalactic names), and the MPC database http://www.minorplanetcenter.net/db_search (for names).

In addition it is not allowed to propose:

   • Names of pet animals;
   • Names of a purely or principally commercial nature;
   • Names of individuals, places or events principally known for political, military or religious activities;
   • Names of living individuals.

  1. the process must be respectful of intellectual property:

    • When starting a campaign involving a list of exoplanets to be named, organisations should first obtain the formal agreement of the discoverers of the listed exoplanets; the discoverers may then participate in the process.
    • These organisations must guarantee that the adopted names resulting from their campaign are free for public use (i.e., for instance, not subject to copyright royalties, as could be the case for names created in fiction works, like books, plays, movies, etc.).

Note that organizations not prepared to follow the abovementioned rules cannot be supported by the IAU, and the names resulting from their process will not be recognized by the IAU. In particular, petitions are not considered an appropriate naming process.

Until the proposal is finalized and the process publicly started with the agreement of the IAU, the discussions between the proposing organization and the IAU must be kept strictly confidential for both parties. After concluding any public consultation, the final submission of the selected names to the IAU, and subsequent discussions with the IAU, must also be kept confidential.. 

When the organization recommends a name, or names, to the IAU, the Executive Committee Working Group Public Naming of Planets and Planetary Satellites will solicit the expertise of the relevant IAU bodies (typically, specialized Commissions and/or Working Groups), and accept input from the organization, to select the name(s) that will constitute the official IAU sanctioned name(s). The selected name(s) will be publicly announced by the IAU. 

It is understood that, if a scientific designation for the object(s) already exists, the public name will not replace it, but will be recognized by the IAU as the appropriate publicly used name for the object(s), and be publicized as such, along with due credit to the organization or individual that proposed it. This public name may then be used internationally along with, or instead of, the scientific designation, permanently and without restrictions.

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