| Discovery | |
|---|---|
| Discovery site | Kepler Space Observatory |
| Discovery date | May 10, 2016 |
| Transit (Kepler Mission) | |
| Orbital characteristics | |
| 0.98 ± 0.14AU | |
| Eccentricity | - |
| 287.378949d | |
| Inclination | 89.97 ± 0.02 |
| Knownsatellites | Kepler-1625b I? |
| Star | Kepler-1625 |
| Physical characteristics | |
| 1.18+0.18 −0.32RJ[1] | |
| Mass | ≤11.60MJ[2] |
Kepler-1625b is a super-Jupiterexoplanet orbiting theSun-like starKepler-1625 about 2,500parsecs (8,200light-years) away in theconstellation ofCygnus.[3] The large gas giant is approximately the same radius asJupiter,[4] and orbits its star every 287.4 days.[5] In 2017, hints of a Neptune-sizedexomoon in orbit of the planet was found usingphotometric observations collected by theKepler Mission.[6][7] Further evidence for a Neptunian moon was found the following year using theHubble Space Telescope, where two independent lines of evidence constrained the mass and radius to be Neptune-like.[4] The mass-signature has been independently recovered by two other teams.[8][9] However, the radius-signature was independently recovered by one of the teams[9] but not the other.[8] The original discovery team later showed that this latter study appears affected by systematic error sources that may influence their findings.[10]
Kepler-1625b is aJovian-sizedgas giant, a type of planet several times greater in radius than Earth and mostly composed of hydrogen and helium. It is 11.4 times Earth's radius, approximately equal to that of the planetJupiter. However, it is up to 11.6 times more massive (about 3,700Earth masses), based on radial velocity observations.[2] This puts it just below thedeuterium-fusing limit, which is around 13Jupiter masses. Any more massive and Kepler-1625b would be abrown dwarf. However, this mass value only corresponds to an 3-sigma upper limit and the mass of the planet remains undetected at this time.[2]
Unlike the gas giants in our Solar System, Kepler-1625b orbits much closer, slightly closer than the orbital radius as the Earth around the Sun.[4] The planet takes 287days (0.786years; 9.43months) to orbitKepler-1625, as a result of the star's slightly greater mass than theSun. Kepler-1625b receives 2.6 times more insolation than the Earth,[4] meaning it lies at the inner edge of thehabitable zone.[11] However, as the planet has likely no solid surface, bodies of liquid water are impossible.
In July 2017, researchers found signs of aNeptune-sizedexomoon (a moon in another solar system) orbiting Kepler-1625b using archivalKepler Mission data.[6][7]
In October 2018, researchers using theHubble Space Telescope published new observations of the starKepler-1625 which revealed two independent lines of evidence indicative of a largeexomoonKepler-1625b I.[4][13] These were a 20-minuteTransit Timing Variation signature that indicated an approximately Neptune-mass moon, and an additional photometric dip that indicated a Neptune-radius moon.[4] The relative phasing of the two signatures was also consistent with that which a real moon would cause, with the effects in anti-phase.[4] The study concluded that theexomoon hypothesis is the simplest and best explanation for the available observations, though warned that it is difficult to assign a precise probability to its reality and urged follow-up analyses.[12][4]
In February 2019, a reanalysis of the combined Kepler and Hubble observations recovered both a moon-like dip and similartransit timing variation signal.[9] However, the authors suggested that the data could also be explained by an inclined hot-Jupiter in the same system that has gone previously undetected, which could be tested using futureDoppler spectroscopy radial velocity measurements. A second independent reanalysis was published in April 2019, which recovered one of the two lines of evidence, the transit timing variation, but the not the second, the moon-like dip.[8] The original discovery team responded to this soon after, finding that this re-analysis exhibits stronger systematics in their reduction which may be responsible for their differing conclusion.[10]