Kepler-22 b

Extrasolar planets

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synonym Kepler-22b (Celestial objects) generally refers to Kepler-22 b

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Kepler-22b (Kepler-22 b, KOI-087.01) Sun like star Kepler 22 Operating in the livable belt Extrasolar planets 。 It is located in Cygnus Middle, about 638 light years (196 Second gap ）Kepler 22 is too dim to be seen with the naked eye. United States Aerospace Bureau（ NASA ）Of Kepler space telescope First observed on May 12, 2009 Kepler 22b Star transit phenomenon was announced in December 2011.^[1] It is the first known Livable zone Planets in orbit, the surface of which may exist Liquid water 。

Kepler 22b Is about 2.4 times the size of the earth,^[2] Although its mass and surface composition are unknown, the composition similar to that of the Earth is excluded, and it may have a liquid or gaseous shell rich in volatile matter. There is evidence that the surface is not subject to extreme greenhouse effect The influence of heating, then the planet surface temperature Moderate. No Atmosphere And Albedo Like the Earth, its heat balance temperature is about 262 K (− 11 ° C), while the Earth's is 255 K (− 18 ° C).

Chinese name: Kepler-22b
Foreign name: Kepler-22 b
Alias: KOI-87 b 、 KOI-87.01 、 KIC 10593626 b
Classification: Extrasolar planets
Discoverer: William Bruch
Discovery time: December 5, 2011^[3]
Quality: About 52.8 M ⊕^[4] (less than this value)
Diameter: About 30000 km^[5] （2.4 R⊕）

surface temperature: Approx. 295 K
Apparent magnitude: 11.5 etc (Star Kepler-22)
Right ascension: 19:16:51s
Declination: +47°53′4″
Distance from ground: 600 light years
Semimajor axis: 0.849 ± 0.018 AU^[6]
Revolution period: 289.862 days^[7] （±0.02）
Rail inclination: 89.764 degrees

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On May 12, 2009, Kepler space telescope On the third day of scientific operation, Kepler-22b's first transit before its star was observed. The third transit was found on December 15, 2010. After that, Spitzer Space Telescope and Ground observation More confirmation data is provided. On December 5, 2011, the discovery of the planet was announced.^[1] William Bruch (William Borucki) Yes NASA California Ames Research Center The scientists of Kepler telescope Project Chief scientist At the same time, he led the discovery.

Kepler-22b Imagination

Mass and radius

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Kepler 22b has a radius about 2.4 times that of the Earth.^[2] Its quality and surface composition are still unknown,^[1]^[8] Only some very rough estimates have been established: under the 3 σ confidence limit, its mass is less than 124 times of the earth's mass, and under the 1 σ confidence interval, its mass is less than 36 times of the earth's mass.^[9] Kipping et al. (2013) Quality cannot be reliably detected (best Fitted value Only 1 σ confidence interval Slightly larger).^[4]

Kepler 22b, which scientists call the "Water World", may be a“ Ocean planet ”。 Although Kepler 22b and GJ 1214 b Different, but it is also located in Habitable zone , so it may also be associated with water rich planets GJ 1214 b Similar. By Stellar system The radial velocity measurement has excluded the Earth like composition with less than 1 σ uncertainty.^[9-10] Therefore, it may have more volatile components with liquid or gaseous shells;^[11] This will make it similar to the smallest known gas planet Kepler-11 f。

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Kepler 22 B revolves around Kepler 22 Extrasolar planets 。^[1]^[8] be located Cygnus , about 587 light years (180 Second gap ）。 It was discovered by Kepler Space Telescope in December 2011.^[12]

Parent star Kepler 22 Is a G-type star mass ratio The sun is 3% smaller, the volume is 2% smaller, the surface temperature is 5518 K (5245 ° C), and the surface temperature of the sun is 5778 K (5505 ° C).^[13] This star is about 4 billion years old.^[14] By contrast, the sun is 4.6 billion years old.^[15] Kepler 22 Apparent magnitude 11.5, which means it is too dark to see with the naked eye.

Currently available planets Track parameters have only Orbital period (about 290 days) and dip angle (about 90 °). Seen from the Earth, Kepler 22b can regularly pass through the circular surface of its parent star to generate transits.^[16] In order to obtain more information about the planetary orbit details, other Planetary exploration Methods, such as radial velocity Law. Kepler-22b Such methods have been implemented on itself since its discovery, but these methods have not yet detected planets Eccentricity Of Exact value Therefore (as of March 2012), astronomers only stated the upper limit of the planet's mass.

Kepler Extrasolar satellite The Search Project (HEK, The Hunt for Exomoons with Kepler) studied the photometry of the planet by Kepler Space Telescope, in order to find any possible Orbiting satellite Resulting transit time and Duration Evidence of change. However, the result is that no such change is found, so it is ruled out that the mass is greater than 0.54 Earth mass The existence of Kepler 22b satellite.^[4]

Habitability

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Kepler 22b is more distant from its parent star Kepler 22 than Earth distance The sun is 15% less.^[16] But from the parent star of Kepler 22b ray radiation 25% less than the sun.^[12] Considering the far average distance and low light radiation, there is a temperature suitable for life on the surface of the planet, but the premise is that there is no extreme greenhouse effect Heat.

Scientists predict that if the planet does not atmosphere Its surface heat balance temperature is about - 11 ° C. If there is a greenhouse effect similar to that caused by the earth's atmosphere, the temperature of the planet's surface is about 22 ° C. However, if Kepler 22b runs in a highly elliptical orbit, its surface temperature will change greatly. Recent estimates indicate that Kepler 22b is in the experience defined by contemporary Venus and early Mars Livable zone The probability is more than 95% (based on the estimation of when these planets may support habitable conditions), but the probability of being located in the traditional habitable zone around the star is less than 5% (estimated according to the one-dimensional cloud free radiation convection model).^[4]

The habitable zone of Kepler-22 system is compared with that of the solar system.

It should be noted that Kepler 22b may be too large for life. Its state may be closer than that of the Earth Neptune , with a rock core and a surface where liquid and gas mix, or the surface of an entirely liquid ocean. In any case, Natalie Batalha, a scientist of the Kepler project, speculated that "if the planet is mainly an ocean and the rock core is very small, then it is impossible to live in such an ocean.".^[17] The possibility of life on this planet prompted SETI to list Kepler 22b as a priority in the research to be carried out.^[18]

This planet is not the first one suitable for live Of terrestrial planet ”。 NASA's Official website When the news was released, the title used was "NASA's Kepler Mission Confirms Its First Planet in Habitable Zone of Sun like Star". The correct translation into Chinese should be "NASA's Kepler Mission Confirms Its First Planet in Sun like star The "first" here refers to the first planet confirmed by the Kepler plan, not the first planet discovered by astronomers Habitable planet 。

Kepler detector It is necessary to observe the starlight darkening four times to determine that this phenomenon is really caused by the planet blocking the starlight - this step is called "confirmation". Among the planet candidates announced by Kepler in February 2011, there are 54 planets that may be located in the "habitable zone", and the "Kepler-22b" announced this time is the first confirmed planet. Among the newly announced planetary candidates, there are still 48 that may be located in the "habitable zone". Therefore, this is also the most livable planet for human beings.^[19-20]

Kepler-22 b parameters

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