Kepler-90h is an extrasolar planet orbiting the star Kepler-90, located within the habitable zone of the G-type main-sequence star Kepler-90, the outermost of eight such planets discovered by NASA's Kepler spacecraft. It is located about 2,545 light-years (780 parsecs) away from Earth in the constellation Draco. This extrasolar planet was found using the transit method, in which the dimming effect that a planet causes as it crosses in front of its star is measured.
Characteristics[]
Mass, radius, and temperature[]
Kepler-90h is a gas giant, a planet which has a radius and mass around the same as that of the planets Jupiter and Saturn. It has a temperature of 292 K (19 °C; 66 °F), close to that of Earth. It has a mass around 1.2 Jupiter mass, and a radius less than or equal to around 1.01 Jupiter mass. This makes it very similar to Jupiter, in terms of mass and radius.
Host star[]
The planet orbits a G-type main-sequence star named Kepler-90. The star has a mass of 1.2 Solar masses and a radius of 1.2 Solar radii. It has a surface temperatures of 6080 K and has an estimated age of around 2 billion years. In comparison, the Sun is about 4.6 billion years old and has a surface temperature of 5778 K.
The star's apparent magnitude, or how bright it appears from Earth's perspective, is 14, so it is too dim to be seen with the naked eye.
Orbital characteristics[]
Kepler-90h orbits its host star about every 331.6 days at a distance of 1.01 AU, very similar to Earth's orbital distance from the Sun (which is 1 AU).
Habitability[]
Kepler-90h resides in the circumstellar "habitable zone" of its star. The planet has a radius of 1.01 Jupiter radius, which makes it too large to be rocky, and is instead likely to be a gas giant. Because of this, the planet itself is probably not be habitable, although some scientists such as Stephen Hawking and Carl Sagan have theorized that lifeforms could evolve in the atmospheres of gas giants.
Hypothetically, large enough moons, with a sufficient atmosphere and pressure, may be able to support liquid water and potentially life. However, such moons do not usually form around planets, they would likely have to be captured from afar; e.g., a protoplanet running astray. A Jupiter-sized planet would likely form moons similar in size to Jupiter's Galilean Moons or Saturn's moon Titan. However, we know that even moons of this size can hold on to atmospheres and have magnetic fields, since Titan has an atmosphere thicker than Earth's and has stable bodies of liquid on its surface. A moon of similar size, Jupiter's Ganymede, has its own magnetic field.
For a stable orbit the ratio between the moon's orbital period Ps around its primary and that of the primary around its star Pp must be < 1/9, e.g. if a planet takes 90 days to orbit its star, the maximum stable orbit for a moon of that planet is less than 10 days. Simulations suggest that a moon with an orbital period less than about 45 to 60 days will remain safely bound to a massive giant planet or brown dwarf that orbits 1 AU from a Sun-like star. In the case of Kepler-90h, this would be practically the same to have a stable orbit.
Tidal effects could also allow the moon to sustain plate tectonics, which would cause volcanic activity to regulate the moon's temperature and create a geodynamo effect which would give the satellite a strong magnetic field.
To support an Earth-like atmosphere for about 4.6 billion years (the age of the Earth), the moon would have to have a Mars-like density and at least a mass of 0.07 Earth mass. One way to decrease loss from sputtering is for the moon to have a strong magnetic field that can deflect stellar wind and radiation belts. NASA's Galileo's measurements hints large moons can have magnetic fields; it found that Jupiter's moon Ganymede has its own magnetosphere, even though its mass is only 0.025 Earth masses.
Discovery[]
In 2009, NASA's Kepler spacecraft was completing observing stars on its photometer, the instrument it uses to detect transit events, in which a planet crosses in front of and dims its host star for a brief and roughly regular period of time. In this last test, Kepler observed 50000 stars in the Kepler Input Catalog, including Kepler-90; the preliminary light curves were sent to the Kepler science team for analysis, who chose obvious planetary companions from the bunch for follow-up at observatories. Observations for the potential exoplanet candidates took place between 13 May 2009 and 17 March 2012. After observing the respective transits, which for Kepler-90h occurred roughly every 331 days (its orbital period), it was eventually concluded that a planetary body was responsible for the periodic 331-day transits. The discovery, was announced on November 12, 2013.