Kepler-90g
A super-puff exoplanet with an unusually inflated atmosphere.
Kepler-90g is a super-puff exoplanet orbiting the early G-type main sequence star Kepler-90, one of eight planets in that system discovered by NASA's Kepler space telescope. It is located about 2840 light-years from Earth in the constellation Draco. The planet was detected via the transit method, measuring the dimming of starlight as it crosses in front of its star.
Quick Facts
- Extrasolarplanet
- yes
- Apsis
- astron
- Discoverer
- Cabrera et al.
- Discovered
- October 2013
- Discovery Method
- Transit
- Semimajor
- 0.71 · 0.08 AU
- Eccentricity
- 0.049 · 0.011 · 0.007
- Star
- Kepler-90
Facts from the source article.
Lore & Background
Kepler-90g orbits its parent star every 210.5 days at a distance of 0.71 astronomical units. Its orbital period changes by 25.7 hours between two consecutive transits, a variation caused by gravitational perturbations from other planets in the system. Changes in the depth and duration of transit events initially led to a hypothesized exomoon orbiting this planet, but that candidate moon was later found to be a false positive. A 2020 analysis of transit-timing variations of Kepler-90g and Kepler-90h yielded a best-fit mass for planet g that falls between the masses of Uranus and Neptune. Combined with a transit-derived radius, the planet was found to have an extremely low density, unusually inflated for its mass and insolation. Several possible explanations for its apparently low density include a puffy planet with a dusty atmosphere or a smaller planet surrounded by a tilted wide ring system, though the ring option is considered less likely due to the lack of evidence for rings in transit data.
Reader's Guide
Kepler-90g is notable as one of eight planets in the Kepler-90 system, a rare example of a star with as many planets as the Solar System. Its super-puff nature—extremely low density despite a mass between Uranus and Neptune—makes it a key object for studying planetary atmospheric inflation mechanisms. The detection of transit-timing variations caused by gravitational interactions with other planets in the system highlights the dynamical complexity of multi-planet systems. The initial exomoon hypothesis, later refuted, illustrates the challenges of interpreting subtle transit signals. The planet's low density, possibly due to a dusty atmosphere or a ring system, remains an open question, underscoring the diversity of exoplanet compositions. Its study contributes to understanding how planets can retain or acquire extended atmospheres under moderate insolation.
Did You Know?
- Kepler-90g is one of eight planets orbiting the star Kepler-90.
- Its orbital period changes by 25.7 hours between consecutive transits due to gravitational perturbations.
- Its mass is between that of Uranus and Neptune.
More in Transiting Exoplanets, Part 4 1-24
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