Kepler-42

Kepler-42, formerly known as KOI-961, is a red dwarf located in the constellation Cygnus and approximately 131 light years from the Sun. It has three known extrasolar planets, all of which are smaller than Earth in radius,[4] and likely also in mass.

Kepler-42

Artist's impression of the Kepler-42 (KOI-961) system
Credit: NASA
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus
Right ascension  19h 28m 52.5688s[1]
Declination 44° 37′ 08.990″[1]
Apparent magnitude (V) 16.12[2]
Characteristics
Spectral type M5V[3]
Astrometry
Radial velocity (Rv)−84.48±0.2[3] km/s
Proper motion (μ) RA: 93.126±0.073[1] mas/yr
Dec.: −417.420±0.067[1] mas/yr
Parallax (π)24.9340 ± 0.0401[1] mas
Distance130.8 ± 0.2 ly
(40.11 ± 0.06 pc)
Details
Mass0.13±0.05[3] M☉
Radius0.17±0.04[3] R☉
Luminosity2.40x10−3.0±0.3 L☉
Temperature3068±174[3] K
Metallicity [Fe/H]−0.48±0.17[3] dex
Rotational velocity (v sin i)2.9±0.4[3] km/s
Other designations
2MASS J19285255+4437096, KIC 8561063, LSPM J1928+4437
Database references
SIMBADdata
KICdata

Characteristics

Kepler-42's mass is estimated to be 0.13 times that of the Sun, and to have a radius 0.17 times that of the Sun, that is, just 1.7 times that of the gas giant Jupiter. Due to its small radius and hence surface area, the luminosity of Kepler-42 is only 0.24% of that of the Sun. Its metallicity is one third of the Sun's. Kepler-42 has an appreciable proper motion of up to 431±8 mas/yr.[3] Due to its small size and low temperature, the star's habitable zone is much closer to the star than Earth is to the Sun.

Planetary system
Earth, Mars and the planets of this system compared to Kepler-20e and Kepler-20f, the first terrestrial-sized exoplanets to be discovered outside of the Solar System
The Kepler-42 system as compared to the Jovian system[note 1]

On 10 January 2012, using the Kepler Space Telescope three transiting planets were discovered in orbit around Kepler-42. These planets' radii range from approximately those of Mars to Venus. The Kepler-42 system is only the second known system containing planets of Earth's radius or smaller (the first was the Kepler-20 system pictured at left). These planets' orbits are also compact, making the system (whose host star itself has a radius comparable to those of some hot Jupiters) resemble the moon systems of giant planets such as Jupiter or Saturn more than it does the Solar System. Despite these planets' small size and the star's being one of the faintest stars in Kepler field with confirmed planets, the detection of these planets was possible due to small size of the star, causing these planets to block a larger proportion of starlight during their transits.

Not all of the orbital parameters of the system are known. For example, as with all transiting planets that have not had their properties established by means of other methods such as the radial velocity method, the orbital eccentricity remains unknown.

Based on the orbits of the planets and the luminosity and effective temperature of the host star, the equilibrium temperatures of the planets can be calculated. Assuming an extremely high albedo of 0.9 and absence of greenhouse effect, the outer planet Kepler-42 d would have an equilibrium temperature of about 280 K (7 °C),[5] similar to Earth's 255 K (−18 °C).[6] Estimates for the known planets are in the tables below:

Temperature
comparisons		 Kepler-42c Kepler-42b Kepler-42d Earth
Global
equilibrium
temperature		728 K
455 °C
851 °F		524 K
251 °C
483.8 °F		454 K
181 °C
357.8 °F		255 K
−18 °C
−0.4 °F
References:[5][note 2]
The Kepler-42 planetary system[2][4][7]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
c <2.06 M⊕ 0.006 0.45328509 ± 9.7x10−7 0 — 0.73 ± 0.20 R⊕
b <2.73 M⊕ 0.0116 1.2137672 ± 4.6x10−6 0 — 0.78 ± 0.22 R⊕
d <0.9 M⊕ 0.0154 1.856169 ± 1.4x10−5 0 — 0.57 ± 0.18 R⊕

Notes
  1. Orbit sizes to scale with each other, but not to the sizes of their respective host bodies
  2. Temperature values for all planets assuming an albedo of 0.3, Earth's value.
gollark: Left-justification:> Left-wing politics supports social equality and egalitarianism, often in critique of social hierarchy.[1][2][3][4] Left-wing politics typically involves a concern for those in society whom its adherents perceive as disadvantaged relative to others as well as a belief that there are unjustified inequalities that need to be reduced or abolished.[1] According to emeritus professor of economics Barry Clark, left-wing supporters "claim that human development flourishes when individuals engage in cooperative, mutually respectful relations that can thrive only when excessive differences in status, power, and wealth are eliminated."[5] No language (except esoteric apioforms) *truly* lacks generics. Typically, they have generics, but limited to a few "blessed" built-in data types; in C, arrays and pointers; in Go, maps, slices and channels. This of course creates vast inequality between the built-in types and the compiler writers and the average programmers with their user-defined data types, which cannot be generic. Typically, users of the language are forced to either manually monomorphise, or use type-unsafe approaches such as `void*`. Both merely perpetuate an unjust system which must be abolished.
gollark: Anyway, center-justify... centrism is about being precisely in the middle of the left and right options. I will imminently left-justify it, so centre-justification WILL follow.
gollark: Social hierarchies are literal hierarchies.
gollark: Hmm. Apparently,> Right-wing politics embraces the view that certain social orders and hierarchies are inevitable, natural, normal, or desirable,[1][2][3] typically supporting this position on the basis of natural law, economics, or tradition.[4]:693, 721[5][6][7][8][9] Hierarchy and inequality may be seen as natural results of traditional social differences[10][11] or competition in market economies.[12][13][14] The term right-wing can generally refer to "the conservative or reactionary section of a political party or system".[15] Obviously, generics should exist in all programming languages ever, since they have existed for quite a while and been implemented rather frequently, and allow you to construct hierarchical data structures like trees which are able to contain any type.
gollark: Ah, I see. Please hold on while I work out how to connect those.

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. "Star: KOI-961 – 3 PLANETS". Extrasolar Planets Encyclopaedia. 2012-01-12. Retrieved 2012-01-12.
  3. Philip S. Muirhead; John Asher Johnson; Kevin Apps; Joshua A. Carter; Timothy D. Morton; Daniel C. Fabrycky; J. Sebastian Pineda; Michael Bottom; Barbara Rojas-Ayala; Everett Schlawin; Katherine Hamren; Kevin R. Covey; Justin R. Crepp; Keivan G. Stassun; Joshua Pepper; Leslie Hebb; Evan N. Kirby; Andrew W. Howard; Howard T. Isaacson; Geoffrey W. Marcy; David Levitan; Tanio Diaz-Santos; Lee Armus; James P. Lloyd (2012). "Characterizing the Cool KOIs III. KOI-961: A Small Star with Large Proper Motion and Three Small Planets". The Astrophysical Journal. 747 (2): 144. arXiv:1201.2189. Bibcode:2012ApJ...747..144M. doi:10.1088/0004-637X/747/2/144.
  4. "KOI-961: A Mini-Planetary System". NASA Ames Research Center Kepler, A Search for Habitable Planets. NASA Ames Research Center Kepler. 2012-01-11. Retrieved 2012-01-11.
  5. "Planet Equilibrium Temperature". Habitable Exoplanets Catalog. Planetary Habitability Laboratory at the University of Puerto Rico. Retrieved 29 February 2012.
  6. "Radiating Equilibrium Temperature". University of Wisconsin Marathon County - Department of Geology/Geography. Archived from the original on 3 September 2006. Retrieved 29 February 2012.
  7. "How many exoplanets has Kepler discovered?". 2015-04-09.
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