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Kepler-89 is a planetary system about 1600 light-years away in the constellation Cygnus. With a visible magnitude of 12.6, it is too faint to be visible with the naked eye. It consists of at least one star and four planets.

The star is a yellow-white main-sequence star (F8V) 3~4 billion years old. It is 65% larger, 25% more massive and about 340 degrees hotter (6116 K, 5843 °C) than the Sun. Its metallicity (relative content of elements heavier than hydrogen and helium) is about 5% larger than that of the Sun.

Kepler-89 b is about twice as dense as the Earth so it is probably made mostly of rocks and metals. Next door, Kepler-89 c is similar in size and mass to Uranus and Neptune. Kepler-89 d is as large as Jupiter but only half as massive as Saturn, so it is probably made mostly of light gases such as hydrogen and helium. Finally, Kepler-89 e is a little less massive but larger than Kepler-89 c, so it has certainly a larger proportion of light elements. The four planets are between 0.05 and 0.3 au from the star (1 au = Sun-Earth distance).

In addition, a low-mass (~0.1 solar mass) stellar companion around 300 au away may complete the system, but its membership remains to be confirmed.


Name Mass(MJ) Radius(RJ) Period(days) Discovery(date)
Kepler-89b 0.033 0.153 3.74 2013
Kepler-89c 0.049 0.386 10.42 2014
Kepler-89d 0.164 0.980 22.34 2015
Kepler-89e 0.041 0.550 54.31 2014





Categories: Planet of the month

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