Kepler-9 is a sunlike

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Lyra Lyra (; Latin for lyre, from Greek ''λύρα'') is a small constellation. It is one of the 48 listed by the 2nd century astronomer Ptolemy, and is one of the modern 88 constellations recognized by the International Astronomical Union. Lyra was ...

. Its

planetary system A planetary system is a set of gravitationally In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interacti ...

, discovered by the Kepler Mission in 2010 was the first detected with the transit method found to contain multiple

planets A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a young ...

Nomenclature and history

Kepler-9 was named for the Kepler Mission, a project headed by

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

that was designed to search for Earth-like planets. In June 2010, some 43 days after Kepler came online, its operating scientists submitted a list of over 700 exoplanet candidates for review. Of those, five were originally suspected to have more than one planet. Kepler-9 was one of the multiplanetary systems; it was identified as such when scientists noticed significant variations in the time intervals at which Kepler-9 was transited. Kepler-9 holds the first multiplanetary system discovered using the transit method. It is also the first planetary system where transiting planets were confirmed through transit timing variations method, allowing to calculate the masses of planets. The discovery of the planets was announced on August 26, 2010.

Characteristics

Kepler-9 is located in the constellation Lyra that lies some 620 parsecs away from Earth. With a mass of and a radius of , Kepler-9 is almost exactly the same size and width of the Sun, being only 7% more massive and 2% wider. Kepler-9 has an

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of 5777 (± 61) K, as compared to the Sun's at 5778 K, and is approximately 32% more

metal-rich In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astronomers use the word ''"metals"'' as a ...

(in terms of iron) than the Sun. Kepler-9 is younger than the Sun, and is estimated to be one billion years old.

Planetary system

There are three confirmed

, all in direct orbit. The outer two planets,

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 ...

(the inner one) and

Kepler-9c Kepler-9c is one of the first seven extrasolar planets, exoplanets, discovered by NASA's Kepler Mission, and one of at least two planets orbiting the star Kepler-9. Kepler-9c and Kepler-9b were the first exoplanets confirmed to be transiting thei ...

(the outer one), are low-density gas giants that are respectively 25% and 17% the mass of Jupiter and around 80% the radius of Jupiter. Both planets have a density less than that of water, similar to

Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...

. The innermost planet, Kepler-9d, is a super-Earth with a radius that is 1.64 times that of Earth, orbiting the star every 1.6 days. It is estimated that there is a 0.59% chance that the discoveries are false. From Kepler-9d (closest to star) to Kepler-9b (second from star), the ratio of their orbits is 1:12. However, the ratio of the orbits of the two outer planets is 1:2, a relationship known as a mean motion resonance. Kepler-9b and Kepler-9c are the first transiting planets detected in such an orbital configuration. The resonance causes the orbital speeds of each planet to change, and thus causes the transit times of the two planets to oscillate. The period of Kepler-9b is increasing by 4 minutes per orbit, while that of Kepler-9c is decreasing by 39 minutes per orbit. These orbital changes allowed the masses of the planets (a parameter not normally obtainable via the transit method) to be estimated using a dynamical model. The mass estimates were further refined using radial velocity measurements obtained with the HIRES instrument of the Keck 1 telescope. Kepler-9b and 9c are thought to have formed beyond the "

frost line The frost line—also known as frost depth or freezing depth—is most commonly the depth to which the groundwater in soil is expected to freeze. The frost depth depends on the climatic conditions of an area, the heat transfer properties of the s ...

". They are then thought to have migrated inward due to interactions with the remains of the protoplanetary disk. They would have been captured into orbital resonance during this migration. In 2021, it was found the orbital plane of Kepler-9b and Kepler-9c are slowly changing, likely under the gravitational influence of the additional giant planet.

References

External links

* Keith Cooper (26 August 2010)
"Kepler finds first double planet transiting system"
''

Astronomy Now ''Astronomy Now'' is a monthly British magazine on astronomy and space. According to the Royal Astronomical Society, ''Astronomy Now'' is the "principal amateur astronomy magazine in Britain" with a reputed circulation of 24,000. The magazine f ...

''. Accessed 7 September 2010. {{Stars of Lyra Planetary systems with three confirmed planets Lyra (constellation) 9 Planetary transit variables G-type main-sequence stars

Nomenclature and history

Characteristics

Planetary system

See also

References

External links