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Solar System and KOI-351 system comparison.jpg
Solar System and KOI-351 system comparison
Spectral type Late F/Early G
Observation data
Epoch {{{epoch}}}      Equinox
Constellation Draco
Right ascension 18h 57m 44s
Declination +49° 18′ 19″
Apparent magnitude (V) 14
Distance 2500 ly
(765 pc)
Mass 1.13 M
Radius 1.2 R
Temperature 5930 K
Metallicity −0.17 ± 0.21
Other designations

Kepler-90 (also KOI-351) is a main-sequence star with a planetary system that has the second-largest number of observed exoplanets in the Milky Way. It is approximately 2,500 light years from Earth.

Kepler-90 is notable for the configuration of its planetary system, which has similarities to the Solar System in which the rocky planets are nearer and gas giants further away. The five inner planets are either super-Earths or mini-Neptunes due to their size. The two outer planets are gas giants. The outermost known planet orbits its host star at about the same distance as Earth from the Sun.

Kepler-90 is designated as KOI-351. During its observation from 2008–2013 it provided evidence for the existence of exoplanets using the transit method, which shows the size of a planet but not its mass. The planets are named based on their distance to the star. Kepler-90b is the innermost and Kepler-90h the outermost of the seven known planets.

Kepler-90 was used to test "validation by multiplicity" confirmation method for Kepler planets. Six inner planets met all the requirements for confirmation. The outermost planet showed transit timing variations indicating that this is a real planet as well.[1]

Planetary system[edit]

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The seven planets are divided to two inner rocky Earth-sized planets, three middle mini-Neptunes and two outer gas giants. Some of these planets show significant transit-timing variations.

The Kepler-90[2] planetary system
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b 0.074 7.008151 89.4° 1.31 R
c 0.089 8.719375 89.68° 1.18 R
d 0.32 59.73667 89.71° 2.88 R.
e 0.42 91.93913 89.79° 2.67 R
f 0.48 124.9144 0.01 89.77° 2.89 R
g 0.71 210.60697 89.8° 8.13 R
h 1.01 331.60059 89.6° 11.32 R

Kepler-90b and c[edit]

Kepler-90b is 31% larger than Earth and Kepler-90c is 19% larger. Kepler-90b and c orbit in a 5:4 mean-motion resonance. This means that in the time it takes Kepler-90b to orbit the star five times, Kepler-90c orbits the star exactly four times so that the planets always meet at the same positions. Similar resonances also exist in the inner moons of Jupiter.

Kepler-90d, e and f[edit]

Planet Kepler-90d orbits the star with a period of 60 days. This is comparable to the orbital period of Mercury around the Sun. It is 2.9 times the size of Earth, making it a super-Earth or a mini-Neptune. Since the mass is only estimated, it is not yet possible to decide which of the two classes this planet belongs to. The planet Kepler-90e is the same size as Kepler-90d (2.7 times Earth's radius). Kepler-90f is 2.9 times Earth's size. These three planets are in 2:3:4 resonance with circular orbits.[3]

Kepler-90g and h[edit]

Kepler-90g and Kepler-90h are gas giants with 8 times and 11 times the diameter of Earth, and have orbital periods of 211 and 331 days, respectively. Kepler-90g could be orbited by a moon.[3] The distance of the outermostplanet Kepler-90h, to its star is about 1.01 AU, or about the average distance between Earth and the Sun. Kepler-90h is on the inner edge of the habitable zone with an equilibrium temperature of 292 K (19 °C, 66 °F)

According to the German news website The Local, the astrophysicists at the German Aerospace Centre (DLR) said on 28 October 2013, that they have discovered "the most extensive planetary system to date".

See also[edit]