Kepler-69c (also known by its Kepler Object of Interest designation ''KOI-172.02'') is a confirmed

super-Earth A super-Earth is an extrasolar planet with a mass higher than Earth's, but substantially below those of the Solar System's ice giants, Uranus and Neptune, which are 14.5 and 17 times Earth's, respectively. The term "super-Earth" refers only to ...

extrasolar planet 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 ...

, likely rocky, orbiting the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

-like star

Kepler-69 Kepler-69 (''KOI-172'', ''2MASS J19330262+4452080'', KIC 8692861') is a G-type main-sequence star similar to the Sun in the constellation Cygnus, located about from Earth. On April 18, 2013 it was announced that the star has two planet ...

, the outermore of two such planets discovered 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. It is located about 2,430

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s (746

parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and ...

s) from

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

. Kepler-69c orbits its star at a distance of from its host star with an orbital period of roughly 242.46

days A day is the time period of a full rotation of the Earth with respect to the Sun. On average, this is 24 hours, 1440 minutes, or 86,400 seconds. In everyday life, the word "day" often refers to a solar day, which is the length between two solar ...

, has a mass at least 2.14x times that of Earth, and has a radius of around 1.7 times that of Earth. Initial findings found that it could possibly be habitable, however updated analysis shows that Kepler-69c resides outside of the inner edge of the habitable zone, and thus is highly likely to resemble the planet

Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...

with temperatures and conditions far too hot to sustain any life, making it uninhabitable. The

discovery Discovery may refer to: * Discovery (observation), observing or finding something unknown * Discovery (fiction), a character's learning something unknown * Discovery (law), a process in courts of law relating to evidence Discovery, The Discovery ...

of the exoplanet was announced in April 2013 by

as part of the ''Kepler'' spacecraft data release. The exoplanet was found by using the

transit method Any planet is an extremely faint light source compared to its parent star. For example, a star like the Sun is about a billion times as bright as the reflected light from any of the planets orbiting it. In addition to the intrinsic difficulty o ...

, in which the dimming effect that a planet causes as it crosses in front of its star is measured.

Physical characteristics

Mass, radius and temperature

Kepler-69c is a

, an exoplanet that has a radius and mass larger than Earth, but smaller than that of the ice giants

Uranus Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus (mythology), Uranus (Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars (mythology), Mars), grandfather ...

and

Neptune Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...

. It has an estimated equilibrium temperature of , but likely has a far hotter surface temperature of . It has an estimated mass of around 2.14 and a radius of 1.71 . These characteristics make it an analog to

, but more massive, so it is called a "

super-Venus A super-Earth is an extrasolar planet with a mass higher than Earth's, but substantially below those of the Solar System's ice giants, Uranus and Neptune, which are 14.5 and 17 times Earth's, respectively. The term "super-Earth" refers only to ...

Host star

The planet orbits a ( G-type) star named

, orbited by a total of two planets. The star has a mass of 0.81 and a radius of 0.93 . It has a surface temperature of 5638 K and has an estimated age of around 9.8 billion years, meaning it is probably nearing the end of its lifetime. In comparison, the Sun is about 4.6 billion years old and has a surface temperature of 5778 K. The star's

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

, or how bright it appears from Earth's perspective, is 13.7. Therefore, Kepler-69 is too dim to be seen with the naked eye.

Orbit

Kepler-69c orbits its host star with about 80% of the Sun's luminosity every 242 days at a distance of 0.64 times that of Earth. This is very similar to that of

's orbital period and distance in the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...

Proposed habitability

The exoplanet, along with the exoplanets

Kepler-62e Kepler-62e (also known by its Kepler Object of Interest designation KOI-701.03) is a super-Earth exoplanet (extrasolar planet) discovered orbiting within the habitable zone of Kepler-62, the second outermost of five such planets discovered by NAS ...

and

Kepler-62f Kepler-62f (also known by its Kepler Object of Interest designation ''KOI-701.04'') is a super-Earth exoplanet orbiting within the habitable zone of the star Kepler-62, the outermost of five such planets discovered around the star by NASA's ''Ke ...

, were announced in the media as being located within the star's "

habitable zone In astronomy and astrobiology, the circumstellar habitable zone (CHZ), or simply the habitable zone, is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure.J. F. Kas ...

", a region where

liquid water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a s ...

could exist on the surface of the

planet 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 you ...

. It was described as being one of the most Earth-like planets, in terms of size and

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

yet found and, according to the scientists, a "prime candidate to host

alien life Extraterrestrial life, colloquially referred to as alien life, is life that may occur outside Earth and which did not originate on Earth. No extraterrestrial life has yet been conclusively detected, although efforts are underway. Such life might ...

". Due to uncertainties in the stellar parameters, the error bars on the value of the incident flux on this planet are quite large, at 1.91 times the level of Earth. Using the nominal parameters, the planet is too close to the star to be habitable, though the uncertainties allow for the possibility that it may actually lie in the innermost region of the habitable zone and be a desert planet, however even with the lowest error bar measurement, a stellar flux of 1.35 ''S''_🜨 would still be high enough to boil away any oceans. A more recent analysis has shown that the planet is likely more analogous to Venus, which is known to be one of the most inhospitable places to life in the Solar System, and thus highly unlikely to be habitable to such organisms. Kepler-69c-_Super-Venus

Discovery

In 2009,

spacecraft was observing stars with 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 ...

, an 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-69; 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. Observations for the potential exoplanet candidates took place between 13 May 2009 and 17 March 2012. After observing the respective transits, which for Kepler-69c occurred roughly every 242 days (its orbital period), it was eventually concluded that a planetary body was responsible for the periodic 242-day transits. The discovery, along with the planetary system of the star

Kepler-62 Kepler-62 is a K-type main sequence star cooler and smaller than the Sun, located roughly 990 light years from Earth in the constellation Lyra. It resides within the field of vision of the ''Kepler'' spacecraft, the satellite that NASA' ...

were announced on April 18, 2013. On 9 May 2013, a congressional hearing by two

U.S. House of Representatives The United States House of Representatives, often referred to as the House of Representatives, the U.S. House, or simply the House, is the lower chamber of the United States Congress, with the Senate being the upper chamber. Together they ...

subcommittees discussed "Exoplanet Discoveries: Have We Found Other Earths?," prompted by the discovery of

exoplanet 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 ...

''Kepler-69c'', along with

and

. A related special issue of the journal ''Science'', published earlier, described the discovery of the exoplanets.

References

Notes

External links

NASA – Mission overview

Kepler – Discoveries – Summary Table
–

.
The Habitable Zone Gallery

– NYT.
Video (02:27) – NASA Finds Three New Planets in "Habitable Zone" (04/18/2013).

Kepler KOI Data Search

KOI-172.02 Data at Exoplanet Archive

Caltech The California Institute of Technology (branded as Caltech or CIT)The university itself only spells its short form as "Caltech"; the institution considers other spellings such a"Cal Tech" and "CalTech" incorrect. The institute is also occasional ...

KOI-172 Star on Star Finder/KPGraham

{{Sky, 19, 33, 02.622, +, 44, 52, 08.00 Cygnus (constellation) Exoplanets discovered in 2013 69c Transiting exoplanets Super-Earths