K2-138
star in the constellation Aquarius
K2-138, also designated EPIC 245950175 or EE-1, is a K-type main-sequence star with a system of six exoplanets discovered by citizen scientists. Four were found in the first two days of the Exoplanet Explorers project on Zooniverse in April 2017, while two more were revealed in further analysis. The system is about 660 light-years (200 parsecs) away in the constellation Aquarius, within K2 Campaign 12.
Planetary system
K2-138 is notable for its large number of planets, all found through the efforts of citizen scientists. They are designated K2-138b, c, d, e, f, and g in order from their host star. The first five were validated by Christiansen et al., while K2-138g was noted as being a likely candidate. However, since there were only two transits of it, K2-138g could not be validated. There was a possibility that the two transits for this candidate were from two individual long-period planets. K2-138g was confirmed by follow-up studies in 2019 and 2021.
All six planets are within the super-Earth and sub-Neptune categories, with radii between about 1.6 R🜨 to 3.3 R🜨.
The public source identifies “K2-138” as star in the constellation Aquarius. This brief keeps that definition visible, then builds a research path around K2-138, star and constellation.
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Vocabulary and entity names are the principal evidence signals here, because they determine the precision of every later search. The source revision retrieved here is dated Sep 12, 2026. The linked authority identifier is Q47471235. None of the 0 selected statements returned an explicit reference. The first chronological checks are 2017, 2019 and 2021.
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This entry incorporates text from “K2-138” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.