Kepler-7b
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Kepler-7b is one of the first five
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 ...
to be confirmed 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 ...
's
Kepler Johannes Kepler (; ; 27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best known for his laws o ...
spacecraft, and was confirmed in the first 33.5 days of Kepler's science operations. It orbits a star slightly hotter and significantly larger than the Sun that is expected to soon reach the end of the
main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Her ...
. Kepler-7b is a
hot Jupiter Hot Jupiters (sometimes called hot Saturns) are a class of gas giant exoplanets that are inferred to be physically similar to Jupiter but that have very short orbital periods (). The close proximity to their stars and high surface-atmosphere temp ...
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 WASP-17b is an exoplanet in the constellation Scorpius that is orbiting the star WASP-17. Its discovery was announced on 11 August 2009. It is the first planet discovered to have a retrograde orbit, meaning it orbits in a direction counter to t ...
. It orbits its host star every five days at a distance of approximately 0,06 AU (9.000.000 km or 5.592.340 mi). Kepler-7b was announced at a meeting of the
American Astronomical Society The American Astronomical Society (AAS, sometimes spoken as "double-A-S") is an American society of professional astronomers and other interested individuals, headquartered in Washington, DC. The primary objective of the AAS is to promote the adv ...
on January 4, 2010. It is the first extrasolar planet to have a crude map of cloud coverage.


Characteristics


Mass, temperature, and orbit

Kepler-7b is a
hot Jupiter Hot Jupiters (sometimes called hot Saturns) are a class of gas giant exoplanets that are inferred to be physically similar to Jupiter but that have very short orbital periods (). The close proximity to their stars and high surface-atmosphere temp ...
, a Jupiter-like exoplanet orbiting close to its star. Its
equilibrium temperature The planetary equilibrium temperature is a theoretical temperature that a planet would be if it were a black body being heated only by its parent star. In this model, the presence or absence of an atmosphere (and therefore any greenhouse effect) is ...
, 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, being surpassed only by
Kepler-6b __NOTOC__ Kepler-6b is an extrasolar planet in the orbit of the unusually metal-rich Kepler-6, a star in the field of view of the NASA-operated Kepler spacecraft, which searches for planets that cross directly in front of, or transit, their host ...
. This is over twelve times hotter than Jupiter. Kepler-7b has a mass of only 0.433 that of
Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, 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 ...
but due to proximity to its star the planet has expanded to a radius of 1.478 that of
Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, 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 ...
. Because of this its mean density is only 0.166 g/cm3, about the same as
expanded polystyrene Polystyrene (PS) is a synthetic polymer made from monomers of the aromatic hydrocarbon styrene. Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin per unit weight. It is a ...
, a substance used to manufacture lightweight, disposable commercial plastic products. Only
WASP-17b WASP-17b is an exoplanet in the constellation Scorpius that is orbiting the star WASP-17. Its discovery was announced on 11 August 2009. It is the first planet discovered to have a retrograde orbit, meaning it orbits in a direction counter to t ...
(0.49 ''M''J; 1.66''R''J) was known to have a lower density at the time of Kepler-7b's discovery. Such low densities are not predicted by current standard theories of planet formation. Kepler-7b orbits its host star every 4.8855 days at a distance of , making it the furthest-orbiting planet of the first five discovered by Kepler.
Mercury Mercury commonly refers to: * Mercury (planet), the nearest planet to the Sun * Mercury (element), a metallic chemical element with the symbol Hg * Mercury (mythology), a Roman god Mercury or The Mercury may also refer to: Companies * Merc ...
, in contrast, orbits at a distance of 0.387 AU every 87.97 days. In addition Kepler-7b has an observed
orbital inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Earth ...
of 86.5º, which means that its orbit is almost edge-on as seen from Earth.


Cloud mapping

Astronomers using data from NASA's Kepler and Spitzer space telescopes have created a cloud map of the planet. It is the first cloud map to be created beyond the Solar System. Kepler's visible-light observations of Kepler-7b's Moon-like phases led to a rough map of the planet that showed a bright spot on its western hemisphere. But these data were not enough on their own to decipher whether the bright spot was coming from clouds or heat. The Spitzer Space Telescope played a crucial role in answering this question.
Jonathan Fortney Jonathan may refer to: *Jonathan (name), a masculine given name Media * ''Jonathan'' (1970 film), a German film directed by Hans W. Geißendörfer * ''Jonathan'' (2016 film), a German film directed by Piotr J. Lewandowski * ''Jonathan'' (2018 ...
, professor of astronomy and astrophysics at
UC Santa Cruz The University of California, Santa Cruz (UC Santa Cruz or UCSC) is a public land-grant research university in Santa Cruz, California. It is one of the ten campuses in the University of California system. Located on Monterey Bay, on the edge of ...
, said: "These clouds may well be composed of rock and iron, since the planet is over ." Brice-Olivier Demory of the Massachusetts Institute of Technology noted that the oceans and continents cannot be detected, but a clear reflective signature has been detected which is interpreted as cloud. Thomas Barclay, Kepler scientist at NASA's Ames Research Center, said: "Unlike those on Earth, the cloud patterns on this planet do not seem to change much over time—it has a remarkably stable climate."


Host star

Kepler-7 Kepler-7 is a star located in the constellation Lyra in the field of view of the Kepler Mission, a NASA operation in search of Earth-like planets. It is home to the fourth of the first five planets that Kepler discovered; this planet, a ...
is the largest host star of the first five planets detected by Kepler, and is situated in the
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 ...
constellation. The star has a
radius In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...
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 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 . The star is near the end of its life on the
main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Her ...
. The star's
metallicity 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 ...
is e/H= 0.11, which means that Kepler-7 has 128% the amount of iron than is detected in the Sun.


Discovery

In 2009,
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 ...
's
Kepler Johannes Kepler (; ; 27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best known for his laws o ...
spacecraft was completing the last of tests on its
photometer A photometer is an instrument that measures the strength of electromagnetic radiation in the range from ultraviolet to infrared and including the visible spectrum. Most photometers convert light into an electric current using a photoresistor, ph ...
, the instrument it uses to detect
transit Transit may refer to: Arts and entertainment Film * ''Transit'' (1979 film), a 1979 Israeli film * ''Transit'' (2005 film), a film produced by MTV and Staying-Alive about four people in countries in the world * ''Transit'' (2006 film), a 2006 ...
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 stars in the
Kepler Input Catalog The Kepler Input Catalog (or KIC) is a publicly searchable database of roughly 13.2 million targets used for the Kepler Spectral Classification Program (SCP) and ''Kepler''. Overview The Kepler SCP targets were observed by the 2MASS project ...
, 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. After a resting period of 1.3 days, Kepler began a nonstop 33.5-day period in which it observed targets uninterrupted until June 15, 2009, when the collected data was downloaded and tested for
false positive A false positive is an error in binary classification in which a test result incorrectly indicates the presence of a condition (such as a disease when the disease is not present), while a false negative is the opposite error, where the test result ...
s. Kepler-7's candidate was not found to be one of these false positives, such as an
eclipsing binary A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in wh ...
star that may generate a light curve that mimics that of transiting planetary companions. Kepler-7 was then observed using
Doppler spectroscopy Doppler spectroscopy (also known as the radial-velocity method, or colloquially, the wobble method) is an indirect method for finding extrasolar planets and brown dwarfs from radial-velocity measurements via observation of Doppler shifts in t ...
using the Fibre-fed Echelle Spectrograph at the Canary Islands'
Nordic Optical Telescope The Nordic Optical Telescope (NOT) is an astronomical telescope located at Roque de los Muchachos Observatory, La Palma in the Canary Islands. The telescope saw first light in 1988, and was officially inaugurated during September 1989. Regular o ...
for ten nights in October 2009, taken with respect to the star HD 182488 to compensate for possible telescope error.
Speckle imaging Speckle imaging describes a range of high-resolution astronomical imaging techniques based on the analysis of large numbers of short exposures that freeze the variation of atmospheric turbulence. They can be divided into the shift-and-add ("'' ...
of the star was taken at WIYN Observatory in Arizona to check for close companions; when none were found, the
High Resolution Echelle Spectrometer The W. M. Keck Observatory is an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state of Hawaii. Both telescopes have aperture primary mirrors, and when comp ...
instrument at the
W.M. Keck Observatory The W. M. Keck Observatory is an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state of Hawaii. Both telescopes have aperture primary mirrors, and when comp ...
on Hawaii, the
Harlan J. Smith Telescope The Harlan J. Smith Telescope is a telescope located at the McDonald Observatory, in Texas, in the United States. This telescope is one of several research telescopes that are part of the University of Texas at Austin observatory perched on Mou ...
at the
McDonald Observatory McDonald Observatory is an astronomical observatory located near unincorporated community of Fort Davis in Jeff Davis County, Texas, United States. The facility is located on Mount Locke in the Davis Mountains of West Texas, with additional facil ...
in Texas, the PRISM camera at the
Lowell Observatory Lowell Observatory is an astronomical observatory in Flagstaff, Arizona, United States. Lowell Observatory was established in 1894, placing it among the oldest observatories in the United States, and was designated a National Historic Landmark ...
, and the
Faulkes Telescope North The Faulkes Telescope North is a clone of the Liverpool Telescope, and is located at Haleakala Observatory in the U.S. state of Hawaii. It is a f/10 Ritchey-Chrétien telescope. The telescope is owned and operated by LCOGT. This telescope and ...
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. Kepler's first discoveries, including the planets
Kepler-4b Kepler-4b, initially known as KOI 7.01, is an extrasolar planet first detected as a transit by the Kepler spacecraft The Kepler space telescope is a disused space telescope launched by NASA in 2009 to discover Earth-sized planets orbiting ot ...
, Kepler-5b,
Kepler-6b __NOTOC__ Kepler-6b is an extrasolar planet in the orbit of the unusually metal-rich Kepler-6, a star in the field of view of the NASA-operated Kepler spacecraft, which searches for planets that cross directly in front of, or transit, their host ...
, Kepler-7b, and
Kepler-8b Kepler-8b is the fifth of the first five exoplanets discovered by NASA's Kepler (satellite), Kepler spacecraft, which aims to discover planets in a region of the sky between the constellations Lyra (constellation), Lyra and Cygnus (constellation) ...
, were first announced on January 4, 2010, at the 215th meeting of the
American Astronomical Society The American Astronomical Society (AAS, sometimes spoken as "double-A-S") is an American society of professional astronomers and other interested individuals, headquartered in Washington, DC. The primary objective of the AAS is to promote the adv ...
in Washington, D.C. In May 2011, the planet was detected by brightness variations of the star cause by reflected starlight from the planet. It was found that Kepler-7b has a relatively high geometric albedo of 0.3.


References


External links

* {{Atmospheres Exoplanets discovered in 2010 Hot Jupiters Giant planets Transiting exoplanets Lyra (constellation) 7b