Kepler-90h

Kepler-90h

Exoplanet		List of exoplanets
Comparison of the orbits of the Kepler-90 system to those of the inner Solar System.
Parent star
Star		Kepler-90
Constellation		Draco
Right ascension	(α)	18h 57m 44.04s
Declination	(δ)	+49° 18′ 18.6″
Apparent magnitude	(mV)	13.89[1]
Distance		2545 ly (780 pc)
Spectral type		G0V
Mass	(m)	1.2 (± 0.1)[2] M☉
Radius	(r)	1.2 (± 0.1)[2] R☉
Temperature	(T)	7003608000000000000♠6080+260 −170[2] K
Metallicity	[Fe/H]	−0.12 (± 0.18)[2]
Age		~2 Gyr
Physical characteristics
Mass	(m)	≤1.2[2] MJ
Radius	(r)	1.01 (± 0.09)[2] RJ
Temperature	(T)	292 K (19 °C; 66 °F)[3]
Orbital elements
Semi-major axis	(a)	1.01 ± 0.11[1] AU
Eccentricity	(e)	0.0 ≤ 0.001[1]
Orbital period	(P)	331.60 ± 0.00037[1] d
Inclination	(i)	89.6 ± 1.3[3]°
Discovery information
Discovery date		November 12, 2013[1]
Discoverer(s)		Kepler spacecraft
Discovery method		Transit[3]
Discovery status		Published
Other designations
KOI-351.01,[4] KOI-351 h, K00351.01, WISE J185744.03+491818.5 h, KIC 11442793 h, 2MASS J18574403+4918185 h
Database references
Extrasolar Planets Encyclopaedia		data
SIMBAD		data
Exoplanet Archive		data
Open Exoplanet Catalogue		data

Kepler-90h (also known by its Kepler Object of Interest designation KOI-351.01) is an exoplanet orbiting within the habitable zone of the early G-type main sequence star Kepler-90, the outermost of seven such planets discovered by NASA's Kepler spacecraft. It is located about 2,545 light-years (780 parsecs, or nearly 7016240780000000000♠2.4078×10¹⁶ km) from Earth in the constellation Draco. The exoplanet was found by 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 that 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 M_J, and a radius less than or equal to around 1.01 R_J. This makes it very similar to Jupiter, in terms of mass and radius.

Host star

The planet orbits a (G-type) star named Kepler-90. The star has a mass of 1.2 M_☉ and a radius 1.2 R_☉. 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^[5] and has a surface temperature of 5778 K.^[6]

The star's apparent magnitude, or how bright it appears from Earth's perspective, is 14. It is too dim to be seen with the naked eye.

Orbital statistics

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 the parent star. The exoplanet, with a radius of 1.01 R_J, is too large to be rocky, and because of this the planet itself may not be habitable. 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 P_s around its primary and that of the primary around its star P_p 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.^[7][8] 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.^[9] 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^[10][11] and create a geodynamo effect which would give the satellite a strong magnetic field.^[12]

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 M_⊕.^[13] 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 M_⊕.^[9]

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 7004500000000000000♠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.^[4]

See also

• Kepler-47c
• HD 69830 d

References

Coordinates: 18^h 57^m 44.04^s, +49° 18′ 18.6″