Kepler-9c is one of the first seven extrasolar planets,

exoplanets An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

, discovered by NASA's

Kepler Mission The Kepler space telescope is a disused space telescope launched by NASA in 2009 to discover Earth-sized planets orbiting other stars. Named after astronomer Johannes Kepler, the spacecraft was launched into an Earth-trailing heliocentric orbi ...

, and one of at least two planets orbiting the star

Kepler-9 Kepler-9 is a sunlike star in the constellation Lyra. Its planetary system, discovered by the Kepler Mission in 2010 was the first detected with the transit method found to contain multiple planets. Nomenclature and history Kepler-9 wa ...

. Kepler-9c and

Kepler-9b __NOTOC__ Kepler-9b is one of the first planets discovered outside the solar system (exoplanets) by NASA's Kepler Mission. It revolves around the star Kepler-9 within the constellation Lyra. Kepler-9b is the largest of three planets detected in ...

were the first exoplanets confirmed to be transiting their star. The planet's discovery was announced by the

team on August 26, 2010 after its initial discovery by Kepler. At the time, it was one of 700 planetary candidates noted by Kepler. Observations of the planet have suggested that it is a hydrogen–helium gas giant that is slightly smaller than Saturn, and that it orbits nearby its star at .225 AU. Kepler-9c and b are notable in that the planets share a pattern of

orbital resonance In celestial mechanics, orbital resonance occurs when orbiting bodies exert regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of small integers. Most commonly, this relationsh ...

, in which the orbit of each planet stabilizes the orbit of the other. During the time it was observed by the spacecraft, the planet's orbit, which lasts on average approximately 38 days, shortened by 39 minutes every

orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...

because of this effect. Its orbit, over time, oscillates slightly above and below a 2:1 ratio with planet ''b''.

Nomenclature and history

As with most exoplanets, the name "Kepler-9c" denotes that it is the second planet discovered in the orbit of the star

. Kepler-9 itself was named after the

, a

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...

project oriented towards discovering planets that are transiting their home stars. The planet was one of 700 planetary candidates considered by Kepler in its first 43 days of operation. It was highlighted as a part of one of five star systems that seemed to hold multiple transiting planets. Kepler-9c and

were confirmed as the first planets discovered to transit the same star. Initial estimates concerning Kepler-9c's mass were refined by follow-up observations made by the Keck 1 Telescope at the W.M. Keck Observatory at Mauna Kea,

Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only state ...

. Keck was able to confirm that Kepler-9c and Kepler-9b were planets that were slightly smaller than planet Saturn.

Characteristics

Kepler-9c is a gas giant that is smaller and slightly less massive than planet Saturn. It is approximately 0.171 M_J, or 17% the mass of planet

Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousandth t ...

. It also has a radius of 0.823 R_J, which makes it slightly smaller (1.5%) than Saturn. The planet is, on average, situated 0.225 AU from the star. It is probable that the planet is composed of

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...

and

helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...

. The planet orbits on the same plane as

, a second and larger gas giant located in the

system. While observing the planet, the Kepler team noticed that Kepler-9b and c orbited in a 1:2 ratio, where Kepler-9b orbits its star every 19 days and Kepler-9c orbits every 38 days. The gravitational pull that each planet has on the other, known as

, keeps the planets in a stable orbit. This phenomenon is the first of its kind seen outside the Solar System. Every time Kepler-9c completed an orbit during the observation period, its orbital period decreased by about 39 minutes. At some point, however, this trend will reverse and its orbit will increase. The lengths of its orbit will oscillate slightly above and below the 2:1 ratio.

References

External links

{{Good article Exoplanets discovered in 2010 Hot Jupiters Giant planets Transiting exoplanets Lyra (constellation) 9c

Nomenclature and history

Characteristics

See also

References

External links