| Extrasolar planet | List of extrasolar planets | |
|---|---|---|
| Parent star | ||
| Star | Kepler-7 | |
| Constellation | Lyra | |
| Right ascension | (α) | 19h 14m 19.6s |
| Declination | (δ) | +41° 5′ 23.3″ |
| Apparent magnitude | (mV) | 13.9[1] |
| Mass | (m) | 1.347 +0.072 −0.054[2] M☉ |
| Radius | (r) | 1.843 +0.048 −0.066[2] R☉ |
| Temperature | (T) | 5933 (± 44)[2] K |
| Metallicity | [Fe/H] | +0.11 (± 0.03)[2] |
| Age | 3.5 (± 1.0)[2] Gyr | |
| Physical characteristics | ||
| Mass | (m) | 0.433 +0.040 −0.041[2] MJ |
| Radius | (r) | 1.478 +0.050 −0.051[2] RJ |
| Density | (ρ) | 0.166 +0.019 −0.020[2] kg m-3 |
| Temperature | (T) | 1540 (± 200)[2] K |
| Orbital elements | ||
| Semimajor axis | (a) | 0.06224[1] AU |
| Eccentricity | (e) | 0[2] |
| Orbital period | (P) | 4.885525 (± 0.000040)[2] d |
| Inclination | (i) | 86.5[1]° |
| Discovery information | ||
| Discovery date | January 4, 2010[3] | |
| Discoverer(s) | ||
| Detection method | Transit (Kepler Mission)[2] | |
| Discovery status | Conference announcement[3] | |
Kepler-7b is one of the first five planets to be confirmed by NASA's Kepler spacecraft, and was confirmed in the first 33.5 days of Kepler's science operations.[2] It is in the orbit of a star that is not as hot as the Sun, but is significantly larger and is expected to soon reach the end of the main sequence.[2] Kepler-7b is a Hot Jupiter that is about half the mass of Jupiter, but is nearly 1.5 times its size; at the time of its discovery, Kepler-7b was the second most diffuse planet known, surpassed only by WASP-17b.[2] It orbits its host star every five days at a distance of approximately 0.06 AU. Kepler-7b was announced at a meeting of the American Astronomical Society on January 4, 2010.
In 2009, NASA's Kepler spacecraft was completing the last of tests 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 50,000 stars in the Kepler Input Catalog, including Kepler-7; 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. Kepler-7 was not one of these original candidates.[2] After a resting period of 1.3 days, Kepler began a nonstop 33.5-day period in which it observed 150,000 targets uninterrupted until June 15, 2009, when the collected data was downloaded and tested for false positives. Kepler-7's candidate was not found to be one of these false positives, such as an eclipsing binary star that may generate a light curve that mimics that of transiting planetary companions. Kepler-7 was then observed using Doppler spectroscopy using the Fibre-fed Echelle Spectrograph at the Canary Islands' Nordic Optical Telescope for ten nights in October 2009, taken with respect to the star HD 182488 to compensate for possible telescope error. Speckle imaging of the star was taken at WIYN Observatory in Arizona to check for close companions; when none were found, the High Resolution Echelle Spectrometer instrument at the W.M. Keck Observatory on Hawaii, the Harlan J. Smith Telescope at the McDonald Observatory in Texas, the PRISM camera at the Lowell Observatory, and the Faulkes Telescope North at the Haleakala Observatory on Maui were also used to analyze Doppler spectroscopy of the planetary candidate. The radial velocity observations confirmed that a planetary body was responsible for the dips observed in Kepler-7's light curve, thus confirming it as a planet.[2]
Kepler's first discoveries, including the planets Kepler-4b, Kepler-5b, Kepler-6b, Kepler-7b, and Kepler-8b, were first announced on January 4, 2010, at the 215th meeting of the American Astronomical Society in Washington, D.C.[3]
Kepler-7 is the largest host star of the first five planets detected by Kepler, and is situated in the Lyra constellation. The star has a radius 184% that of the Sun. Kepler-7 also has 135% the Sun's mass, and thus is larger and more massive (though less dense than) the Sun. It is slightly hotter than the Sun, as Kepler-7 has an effective temperature of 5933 K.[4] The star is near its end of its life on the main sequence.[2] The star's metallicity is [Fe/H] = 0.11, which means that Kepler-7 has 128% the amount of iron than is detected in the Sun.[4]
Kepler-7b is a hot Jupiter, a Jupiter-sized gas giant exoplanet orbiting close to its star. Its equilibrium temperature, due to its proximity to its star, is hot, and is measured at nearly 1540 K. However, of the first five planets discovered by Kepler, it is the second coolest, surpassed only by Kepler-6b.[1] This is over twelve times hotter than Jupiter.[1] Kepler-7b has a mass that is 0.433 times that of Jupiter, although it has been expanded to a size that is 1.478 times the radius of Jupiter. Because of this, its density is only 0.166 g/cm3, about the same as polystyrene, a substance used to manufacture lightweight, disposable commercial plastic products. Only WASP-17b (0.49MJ; 1.66RJ)[5] was known to have a lower-known density at the time of Kepler-7b's discovery.[2] Such low densities are not predicted by current standard theories of planet formation.[6] Kepler-7b orbits its host star every 4.8855 days at a distance of 0.06224 AU, making it the furthest-orbiting planet of the first five discovered by Kepler. In addition, Kepler-7b has an observed orbital inclination of 86.5º, which means that it orbit is almost edge-on as seen from Earth.[1] Mercury, in contrast, orbits at a distance of .387 AU every 87.97 days.[7]
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