Kepler-1625 is a 14th-

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

solar-mass

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

located in the constellation of Cygnus approximately away. Its mass is within 5% of that of the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

, but its radius is approximately 70% larger reflecting its more evolved state. A candidate

gas giant A gas giant is a giant planet composed mainly of hydrogen and helium. Jupiter and Saturn are the gas giants of the Solar System. The term "gas giant" was originally synonymous with "giant planet". However, in the 1990s, it became known that Uranu ...

exoplanet was detected by the

Kepler Mission The Kepler space telescope is a defunct space telescope launched by NASA in 2009 to discover Earth-sized planets orbiting other stars. Named after astronomer Johannes Kepler, the spacecraft was launched into an Earth-trailing heliocentric orb ...

around the star in 2015, which was later validated as a real planet to >99% confidence in 2016. In 2018, the Hunt for Exomoons with Kepler project reported evidence for a Neptune-sized

exomoon Artist's impression of candidate exomoon Kepler-1625b I orbiting its planet. An exomoon or extrasolar moon is a natural satellite that orbits an exoplanet or other non-stellar extrasolar body. Exomoons are difficult to detect and confirm us ...

around this planet, based on observations from NASA's

Kepler mission The Kepler space telescope is a defunct space telescope launched by NASA in 2009 to discover Earth-sized planets orbiting other stars. Named after astronomer Johannes Kepler, the spacecraft was launched into an Earth-trailing heliocentric orb ...

and the

Hubble Space Telescope The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...

. Subsequently, the evidence for and reality of this exomoon candidate has been subject to debate.

Stellar characteristics

Kepler-1625 is an approximately solar-mass star and yet is 1.7 times larger in diameter. Its effective temperature is around 5,550 K, slightly lower than that of the Sun. These parameters suggest that Kepler-1625 may be a yellow

subgiant A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution ...

nearing the end of its life, with an age of approximately 8.7 billion years. The star has been observed to be photometrically quiet, with periodic variability below 0.02%. Kepler-1625 is located approximately 7,200 light-years away in the constellation Cygnus.

Planetary system

The star is known to have one validated planet. Designated Kepler-1625b, it is a Jovian-sized planet orbiting its star every 287.3 Earth days. No other candidate transiting planets have been found around the star.

Potential exomoon

The

recorded three planetary transits of Kepler-1625b from 2009 to 2013. From these, anomalous out-of-transit flux decrements indicated the possible existence of a

Neptune Neptune is the eighth and farthest known planet from the Sun. It is the List of Solar System objects by size, fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 t ...

-sized

, as first reported by the Hunt for Exomoons with Kepler project in 2018. The Kepler data were inconclusive and so the planetary transit was re-observed by the

in October 2018. The light curve from Hubble exhibited evidence for both a moon-like transit and a

transit timing variation Transit-timing variation is a method for detecting exoplanets by observing variations in the timing of a transit method, transit. This provides an extremely sensitive method capable of detecting additional planets in the system with masses potent ...

, both of which were consistent as being caused by the same Neptune-sized moon in orbit of Kepler-1625b. The transit timing variation has been independently recovered by two teams analyzing the same data. One of these teams also independently recovered the moon-like transit, but suggest that

radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity ...

measurements are needed to exclude the possibility of a close-in masquerading planet. The other team are unable to recover the moon-like transit and suggested it may be an artifact of the data reduction. This conclusion was challenged by the original team soon after, who showed that the other analysis exhibits larger systematics that may explain their differing conclusion.

References

{{Sky, 19, 41, 43.04, +, 39, 53, 11.6 Planetary systems with one confirmed planet Planetary transit variables 5084 J19414304+3953115 Cygnus (constellation) G-type subgiants

Stellar characteristics

Planetary system

Potential exomoon

See also

References