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

exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first det ...

, likely rocky, orbiting the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

-like star Kepler-69, the outermore of two such planets discovered by

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

'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 of p ...

'' spacecraft. It is located about 2,430

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

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 Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

. 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 (86,400 seconds). As a day passes at a given location it experiences morning, afternoon, evening, and night. This daily cyc ...

, has a mass at least 2.14 times that of Earth, and has a radius of around 2.2 times that of Earth. Initial findings found that it could possibly be habitable, however updated analysis shows that Kepler-69c resides in the inner edge of the

habitable zone In astronomy and astrobiology, the habitable zone (HZ), or more precisely the circumstellar habitable zone (CHZ), is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressu ...

or even outside of habitable zone, and thus is highly likely to resemble the planet

Venus Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker ...

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 Methods of detecting exoplanets usually rely on indirect strategies – that is, they do not directly image the planet but deduce its existence from another signal. Any planet is an extremely faint light source compared to its parent star. For e ...

, 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 super-Earth, 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. It is a gaseous cyan-coloured ice giant. Most of the planet is made of water, ammonia, and methane in a Supercritical fluid, supercritical phase of matter, which astronomy calls "ice" or Volatile ( ...

and

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

. 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 the planet

, but more massive, so it is called a " super-Venus".

Host star

The planet orbits a ( G-type) star named Kepler-69, 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 Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...

, 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 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 "Sola ...

Proposed habitability

The exoplanet, along with the exoplanets Kepler-62e 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 Kep ...

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

", a region where

liquid water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known living organisms ( ...

could exist on the surface of the

planet A planet is a large, Hydrostatic equilibrium, rounded Astronomical object, astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets b ...

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

temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...

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

alien life Extraterrestrial life, or alien life (colloquially, aliens), is life that originates from another world rather than on Earth. No extraterrestrial life has yet been scientifically conclusively detected. Such life might range from simple forms ...

". 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, ...

, an instrument it uses to detect

transit Transit may refer to: Arts and entertainment Film * ''Transit'' (1980 film), a 1980 Israeli film * ''Transit'' (1986 film), a Canadian short film * ''Transit'' (2005 film), a film produced by MTV and Staying-Alive about four people in countrie ...

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, 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 from Earth in the constellation Lyra (constellation), Lyra. It resides within the field of vision of the Kepler (spacecraft), ''Kepler'' spacecraft ...

were announced on April 18, 2013. On 9 May 2013, a congressional hearing by two U.S. House of Representatives subcommittees discussed "Exoplanet Discoveries: Have We Found Other Earths?," prompted by the discovery of

''Kepler-69c'', along with Kepler-62e 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) is a private university, private research university in Pasadena, California, United States. The university is responsible for many modern scientific advancements and is among a small g ...

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