, there have been no positive confirmations of satellites of extra-solar planets (exomoons); however, some evidence in favour of their existence has been produced.
Timeline
— It has been surmised that J1407b, a possibly planetary-mass object that eclipsed the star V1400 Centauri (aka. J1407) in 2007, may have a few moons based on gaps observed in its circumstellar disk or ring system. Later studies have since found that J1407b is most likely a free-floating sub-brown dwarf or rogue planet, possibly less than 6 Jupiter masses. — The confirmed hot Jupiter planet WASP-12b may also possess a moon.Российские астрономы впервые открыли луну возле экзопланеты (in Russian) – "Studying of a curve of change of shine of WASP-12b has brought to the Russian astronomers unusual result: regular splashes were found out.<...> Though stains on a star surface also can cause similar changes of shine, observable splashes are very similar on duration, a profile and amplitude that testifies for benefit of exomoon existence." , — A candidate exomoon of a free-floating planet MOA-2011-BLG-262L, was announced, but due to degeneracies in the modelling of the microlensing event, the observations can also be explained as a Neptune-mass planet orbiting a low-mass red dwarf, a scenario the authors consider to be more likely. In 2024 the latter scenario was confirmed. — researchers using the Hubble Space Telescope published observations of the candidate exomoon Kepler-1625b I, which suggest that the host planet is likely several Jupiter masses, while the exomoon may have a mass and radius similar to Neptune. The study concluded that the exomoon hypothesis is the simplest and best explanation for the available observations, though warned that it is difficult to assign a precise probability to its existence and nature. — reanalysis concluded that the data was fit better by a planet-only model. According to this study, the discrepancy was an artifact of the data reduction, and Kepler-1625b I likely does not exist. – A hypothesis involving potential transits of large exomoons being detached from their planets (see ploonet) was posited to explain the light flux-variations of the Tabby's Star, which were identified from the data collected by Kepler space telescope. — A paper by Chris Fox and Paul Wiegert examined the Kepler dataset for indications of exomoons solely from transit timing variations. Eight candidate signals were found that were consistent with an exomoon, however the signals could also be explained by the presence of another planet. Fox and Wiegert's conclusion was more and higher quality transit timing data would be required to establish whether these are truly moons or not. David Kipping re-derived the timings of six of the eight targets (based on a pre-peer review version) and evaluated the TTV evidence as uncompelling. The same study finds that Kepler-1625b I remains an exomoon candidate. — astronomers reported an habitable-zone 1.7 exomoon candidate transiting one of the components in the planetary-mass binary 2MASS J1119-1137AB. — an exomoon candidate was reported around the planet Kepler-1708b, and because it is orbiting a planet at approximately 1.6 AU from a star that is slightly more luminous than the Sun, it too could be within the habitable zone. However, this candidate is based on limited observations (only two transits) and some consider the data to be non-convincing. — another exomoon candidate was reported around the planet Kepler-1513b (KOI-3678.01). Unlike the previous giant exomoon candidates of Kepler-1625 and Kepler-1708, this exomoon would be terrestrial-mass, ranging from 0.76 Lunar masses to 0.34 Earth masses depending on the planet's mass and moon's orbital period. — a follow-up study by the same team found that the observed TTVs are caused by a second planet in the system, and not by a moon. — The exomoon candidate around Kepler-1625b was again challenged, along with the Kepler-1708b candidate. This study argues that the statistical significance of these exomoon candidates is lower than previously claimed (with false positive probabilities of 10.9% and 1.6%, respectively) and that true giant exomoons would have stronger evidence. Evidence for exomoon transits may be caused by stellar activity in the Kepler light curves. Kipping's team published a response arguing that these exomoon candidates remain possible. — New measurements with the Very Large Telescope of the star WASP-49 gave more evidences favoring the presence of a possible volcanically active-moon around the hot Jupiter WASP-49b. A similar study in 2025 with JWST suggested that the sulfur dioxide detection in the atmosphere of WASP-39b is due to the presence of a volcanically active-exomoon. 2025 — While investigating HD 206893 B with the GRAVITY instrument at the Very Large Telescope (VLT), signs of a potential very massive exomoon was detected around HD 206893 B. If confirmed, the exomoon's mass should be 40% of Jupiter's mass. — The European Southern Observatory's Very Large Telescope reported evidence of a possible exomoon-like object orbiting the brown dwarf CD-35 2722 B in the CD-35 2722 system, in a study published in the Nature journal.https://www.space.com/astronomy/exoplanets/astronomers-may-have-discovered-the-1st-moon-outside-of-our-solar-system-or-is-it-something-weirderhttps://phys.org/news/2026-07-jupiter-mass-exomoon-orbiting-brown.html
Table
Host starof thehost planet(s) Planet designation Planet mass Planetsemimajoraxis(AU) Exomoonsemimajoraxis Exomoonmass () Notes N/A J1407b N/A 0.396–0.421 AU <0.8 One possible exomoon residing in a 4 million km-wide gap in J1407b's circumplanetary disk. Other ring gaps in J1407b's disk may also contain exomoons. J1407b may not actually exist and might just be a large dust cloud.N/A2MASS J1119-1137A or B3.7 3.6 ± 0.9separation from each other0.004 - 0.009 AU0.5 - 1Found using the transit method. A habitable-zone exomoon candidate transiting a directly imaged free-floating planet or isolated planetary-mass object.N/A2MASS J2117-29407 N/A0.005 AU~0.5Candidate exomoon transit detected in Spitzer observations of 2MASS J21171431-2940034. DH Tauri DH Tauri b 10.6 330 10 AU 317.827 Candidate Jupiter-mass satellite from direct imaging. If confirmed, it could also be considered a planet orbiting a brown dwarf. HD 189733 HD 189733 b 1.13 0.031 0.0087 AU ? Found by studying periodic increases and decreases in light given off from HD 189733 b. Outside of planet's Hill sphere. <0.00112 AU ~ 0.015 Exo-Io candidate; The sodium and potassium data at HD 189733b is consistent with evaporating exomoons and/or their corresponding gas torus. Kepler-409 Kepler-409b 1.00 0.320 0.222 RHill 0.300 Possible exomoon from transit timing variations, since deemed unlikely. Kepler-517 Kepler-517b 7.59 0.298 0.278 RHill 0.499 Possible exomoon from transit timing variations, since deemed unlikely. Kepler-809 Kepler-809b 38.02 0.308 0.289 RHill 2.931 Possible exomoon from transit timing variations. Kepler-857 Kepler-857b 14.13 0.376 0.208 RHill 1.636 Possible exomoon from transit timing variations. Kepler-1000 Kepler-1000b 19.95 0.534 0.235 RHill 1.551 Possible exomoon from transit timing variations, since deemed unlikely. Kepler-1326 Kepler-1326b 24.55 0.2691 0.295 RHill 6.057 Possible exomoon from transit timing variations, since deemed unlikely. Kepler-1442 Kepler-1442b 14.13 0.405 0.208 RHill 1.586 Possible exomoon from transit timing variations, since deemed unlikely. Kepler-1625 Kepler-1625b 0.98 0.022 AU 19.0 Name: Kepler-1625b I. Possible Neptune-sized exomoon or double planet, indicated by transit observations. Kepler-1708 Kepler-1708b 1.64 0.005 AU (11.7 RP) Name: Kepler-1708b Possible Neptune-sized exomoon or double planet, indicated by transit observations. KOI-868 KOI-868.01 0.689 0.6534 0.0221 AU 0.31 Possible exomoon from transit timing variations. Potentially habitable exomoon with a radius of 1.23 . KOI-268 KOI-268.01 9.33 0.47 0.217 RHill 0.817 Possible exomoon from transit timing variations, since deemed unlikely. N/A MOA-2015-BLG-337L 9.85 N/A 0.24 AU 33.7 Found by microlensing; however it is unknown if the system is a super-Neptune-mass planet orbiting a free-floating planet, or a binary brown dwarf system.WASP-12WASP-12b1.465 0.0232 – (radius)Российские астрономы впервые открыли луну возле экзопланеты (in Russian) - "Studying of a curve of change of shine of WASP-12b has brought to the Russian astronomers unusual result: regular splashes were found out.<...> Though stains on a star surface also can cause similar changes of shine, observable splashes are very similar on duration, a profile and amplitude that testifies for benefit of exomoon existence." 6 RP – Found by studying periodic increases and decreases in light given off from WASP-12b. Outside of planet's Hill sphere.WASP-39WASP-39b0.275 0.0486 –~ 0.015 WASP-49 WASP-49b 0.37 0.0379 < 1.74 RP ~ 0.015 Exo-Io candidate; The sodium exosphere around WASP-49b could be due to a volcanically active Io-like exomoon. WASP-76 WASP-76b 0.92 0.033 1.125 RP ~ 0.015 Exo-Io candidate; Sodium detected via absorption spectroscopy around WASP-76b is consistent with an extrasolar toroidal atmosphere generated by an evaporating exomoon. WASP-121 WASP-121b 1.184 0.02544 ~ 1.9 RP ~ 0.015 Exo-Io candidate; The sodium detected via absorption spectroscopy around WASP-121b is consistent with an extrasolar gas torus possibly fueled by a hidden exo-Io. HD 206893 HD 206893 B ~ 0.22 AU ~ 130 Very large mass (around 40% of Jupiter's mass). CD-35 2722 CD-35 2722 B AU ≥ (≥ ) First unambiguous exosatellite or exomoon candidate detected though it is uncertain whether this exosatellite would fulfil the presently undefined criteria for qualifying as an exomoon given that CD-35 2722 B is likely to be brown dwarf based on its mass and the exosatellite is massive enough to be a planet.
See also Exomoon Exoplanet Star Lists of stars Lists of exoplanets
References