Kepler-9b
Encyclopedia
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 Kepler system by transit method; its mass is slightly smaller than the planet Saturn
, and it is the largest planet in its system. Kepler-9b and Kepler-9c
display a phenomenon called orbital resonance
, in which gravitational pull from each planet alters and stabilizes the orbit of the other. The planet's discovery was announced on August 26, 2010.
. The star, in turn, was named for the Kepler Mission
, a NASA
project designed to search for Earth
-like planets. Kepler-9's planets were among 700 planetary candidates collected during Kepler's first 43 days online. The system in particular was flagged as one of five systems that appeared to have held more than one transiting exoplanet. Kepler-9b's discovery was announced on August 26, 2010. It was the part of the first confirmed star system in which multiple planets transited the same star.
The planet was confirmed by the Kepler satellite by the transit method, in which the planet passes across the face of its star in relation to Earth, dimming that star's light by a small amount; this light difference is then used to determine the planet and several of its characteristics, including size and distance from its home star.
Initial estimates for Kepler-9b's mass were refined by the W. M. Keck Observatory at Mauna Kea
, Hawaii
. In doing so, scientists found that Kepler-9b is the larger of the two gas planets discovered in the Kepler-9 system, although in mass it is smaller than planet Saturn
.
; thus, it is about one-fourth the mass of planet Jupiter
. It has a radius of approximately .842 RJ, or about 80% the radius of Jupiter. The planet orbits Kepler-9 every 19.243 days, and it lies some .14 AU
from the star. To compare, planet Mercury
's average distance from the Sun
is .387 AU and takes 87.969 days to complete an orbit. Kepler-9b is the second closest planet to its star in the Kepler-9 system.
The first known case of orbital resonance
in exoplanets has been noted between Kepler-9b and Kepler-9c
. The two planets, whose orbits correspond in a roughly 1:2 ratio, maintain the orbit of the other by gravitational tug. Kepler-9b's orbit grows, on average, four minutes longer every orbital period
. Eventually, this trend will reverse and increase. Over time, it can be seen that the planets' orbits oscillate slightly above and below the 1:2 ratio. Alycia Weinberger of the Carnegie Institution has stated that the Kepler-9 gas giants probably formed further away from the star than they are, and the appearance of the orbital resonance phenomenon may help explain the history of their inward migration.
Extrasolar planet
An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
) by NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
's Kepler Mission. It revolves around the star Kepler-9
Kepler-9
Kepler-9 is a sunlike star in the constellation Lyra. It is situated in the Kepler Mission's field of view. Kepler-9 has three confirmed extrasolar planets, all discovered by Kepler using the transit method. The discovery of the first two planets was announced on August 26, 2010, and of the third...
within the constellation Lyra
Lyra
Lyra is a small constellation. It is one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations recognized by the International Astronomical Union. Its principal star, Vega — a corner of the Summer Triangle — is one of the brightest...
. Kepler-9b is the largest of three planets detected in the Kepler system by transit method; its mass is slightly smaller than the planet Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
, and it is the largest planet in its system. Kepler-9b and Kepler-9c
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 their star. The planet's discovery was announced by the...
display a phenomenon called orbital resonance
Orbital resonance
In celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other, usually due to their orbital periods being related by a ratio of two small integers. Orbital resonances greatly enhance the mutual gravitational influence of...
, in which gravitational pull from each planet alters and stabilizes the orbit of the other. The planet's discovery was announced on August 26, 2010.
Nomenclature and history
Kepler-9b's name denotes that it is the first exoplanet discovered in orbit around the star Kepler-9Kepler-9
Kepler-9 is a sunlike star in the constellation Lyra. It is situated in the Kepler Mission's field of view. Kepler-9 has three confirmed extrasolar planets, all discovered by Kepler using the transit method. The discovery of the first two planets was announced on August 26, 2010, and of the third...
. The star, in turn, was named for the Kepler Mission
Kepler Mission
The Kepler spacecraft is an American space observatory, the space-based portion of NASA's Kepler Mission to discover Earth-like planets orbiting other stars. The spacecraft is named in honor of the 17th-century German astronomer Johannes Kepler...
, a NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
project designed to search for Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
-like planets. Kepler-9's planets were among 700 planetary candidates collected during Kepler's first 43 days online. The system in particular was flagged as one of five systems that appeared to have held more than one transiting exoplanet. Kepler-9b's discovery was announced on August 26, 2010. It was the part of the first confirmed star system in which multiple planets transited the same star.
The planet was confirmed by the Kepler satellite by the transit method, in which the planet passes across the face of its star in relation to Earth, dimming that star's light by a small amount; this light difference is then used to determine the planet and several of its characteristics, including size and distance from its home star.
Initial estimates for Kepler-9b's mass were refined by the W. M. Keck Observatory at Mauna Kea
Mauna Kea
Mauna Kea is a volcano on the island of Hawaii. Standing above sea level, its peak is the highest point in the state of Hawaii. However, much of the mountain is under water; when measured from its oceanic base, Mauna Kea is over tall—significantly taller than Mount Everest...
, Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
. In doing so, scientists found that Kepler-9b is the larger of the two gas planets discovered in the Kepler-9 system, although in mass it is smaller than planet Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
.
Characteristics
Kepler-9b is a gas planet that has an approximate mass of .252 MJJupiter mass
Jupiter mass , is the unit of mass equal to the total mass of the planet Jupiter . Jupiter mass is used to describe masses of the gas giants, such as the outer planets and extrasolar planets. It is also used in describing brown dwarfs....
; thus, it is about one-fourth the mass of planet Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
. It has a radius of approximately .842 RJ, or about 80% the radius of Jupiter. The planet orbits Kepler-9 every 19.243 days, and it lies some .14 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
from the star. To compare, planet Mercury
Mercury (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...
's average distance from the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
is .387 AU and takes 87.969 days to complete an orbit. Kepler-9b is the second closest planet to its star in the Kepler-9 system.
The first known case of orbital resonance
Orbital resonance
In celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other, usually due to their orbital periods being related by a ratio of two small integers. Orbital resonances greatly enhance the mutual gravitational influence of...
in exoplanets has been noted between Kepler-9b and Kepler-9c
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 their star. The planet's discovery was announced by the...
. The two planets, whose orbits correspond in a roughly 1:2 ratio, maintain the orbit of the other by gravitational tug. Kepler-9b's orbit grows, on average, four minutes longer every orbital period
Orbital period
The orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...
. Eventually, this trend will reverse and increase. Over time, it can be seen that the planets' orbits oscillate slightly above and below the 1:2 ratio. Alycia Weinberger of the Carnegie Institution has stated that the Kepler-9 gas giants probably formed further away from the star than they are, and the appearance of the orbital resonance phenomenon may help explain the history of their inward migration.