View source for Kepler-442

{{Short description|Main sequence star in the constellation Lyra}}
{{Starbox begin
| name = Kepler-442
}}
{{Starbox observe
| epoch = J2000
| constell = [[Lyra (constellation)|Lyra]]
| ra = {{RA|19|01|27.9743}}<ref name="Gaia DR3"/>
| dec = {{DEC|+39|16|48.224}}<ref name="Gaia DR3"/>
| appmag_v = 14.976<ref name="Keplercitepaper">{{cite journal|bibcode=2015ApJ...800...99T|arxiv=1501.01101|title=Validation of 12 Small Kepler Transiting Planets in the Habitable Zone|journal=The Astrophysical Journal|volume=800|issue=2|pages=99|last1=Torres|first1=Guillermo|last2=Kipping|first2=David M.|last3=Fressin|first3=Francois|last4=Caldwell|first4=Douglas A.|last5=Twicken|first5=Joseph D.|last6=Ballard|first6=Sarah|last7=Batalha|first7=Natalie M.|last8=Bryson|first8=Stephen T.|last9=Ciardi|first9=David R.|last10=Henze|first10=Christopher E.|last11=Howell|first11=Steve B.|last12=Isaacson|first12=Howard T.|last13=Jenkins|first13=Jon M.|last14=Muirhead|first14=Philip S.|last15=Newton|first15=Elisabeth R.|last16=Petigura|first16=Erik A.|last17=Barclay|first17=Thomas|last18=Borucki|first18=William J.|last19=Crepp|first19=Justin R.|last20=Everett|first20=Mark E.|last21=Horch|first21=Elliott P.|last22=Howard|first22=Andrew W.|last23=Kolbl|first23=Rea|last24=Marcy|first24=Geoffrey W.|last25=McCauliff|first25=Sean|last26=Quintana|first26=Elisa V.|year=2015|doi=10.1088/0004-637X/800/2/99|s2cid=8512655}}</ref>
}}
{{Starbox character
| type = [[Main sequence]]
| class= K5V<ref name="FraserCainAgain"/><ref name="ExoplanetNASA"/>
}}
{{Starbox astrometry
| radial_v = 
| prop_mo_ra = {{val|7.784|(18)}}
| prop_mo_dec = {{val|1.882|(19)}}
| pm_footnote = <ref name="Gaia DR3"/>
| parallax = 2.7269
| p_error = 0.0165
| parallax_footnote = <ref name="Gaia DR3"/>
| absmag_v = {{val|7.73|0.28|0.25}}<ref name="Keplercitepaper"/><!--Kepler Absolute Magnitude = 4.79-->
 }}
{{Starbox detail
| mass = 0.61 ± 0.03<ref name="Keplercitepaper"/>
| radius = 0.60 ± 0.02<ref name="Keplercitepaper"/>
| temperature = 4402 ± 100<ref name="Keplercitepaper"/>
| metal_fe = −0.37 ± 0.10<ref name="Keplercitepaper"/>
| luminosity_bolometric = 0.117<ref name="PHL">[http://www.hpcf.upr.edu/~abel/phl/hec_plots/hec_orbit/hec_orbit_Kepler-442_b.png Kepler 442b] hpcf.upr.edu</ref>
| luminosity_visual = 0.069<ref group=nb>With the absolute visual magnitude of Kepler-442, <math>\scriptstyle M_{V_{\ast}} = 7.73</math>, and the Sun, <math style="vertical-align:-36\%;">\scriptstyle M_{V_{\odot}} = 4.83</math>, the visual luminosity of Kepler-442 is calculated from: <math>\scriptstyle \frac{L_{V_{\ast}}}{L_{V_{\odot}}} = 10^{0.4\left(M_{V_{\odot}} - M_{V_{\ast}}\right)}</math></ref>
| age_gyr = {{val|2.9|8.1|0.2}}<ref name="Keplercitepaper"/>
}}
{{Starbox catalog
| names = {{odlist | 2MASS=J19012797+3916482 | Gaia DR2=2100258047339711488 | KIC=4138008 | KOI=4742 }}<ref name="Simbad"/>
}}
{{Starbox reference
| Simbad = KOI-4742
| EPE = Kepler-442
}}
{{Starbox end}}

'''Kepler-442''' is a [[K-type main-sequence star]] approximately 1,196 [[Light-year|light years]] from [[Earth]] in the constellation [[Lyra (constellation)|Lyra]]. It is located within the field of vision of the [[Kepler (spacecraft)|Kepler spacecraft]], the satellite that [[NASA]]'s [[Kepler Mission]] used to detect planets that may be transiting their stars. On January 6, 2015, along with the stars of [[Kepler-438]] and [[Kepler-440]], it was announced that the star has an extrasolar planet (a [[super-Earth]]) orbiting within the [[habitable zone]], named [[Kepler-442b]].<ref name="Keplercitepaper"/>

==Nomenclature and history==
[[File:LombergA1024.jpg|thumb|left|300px|The ''[[Kepler (spacecraft)|Kepler Space Telescope]]'' search volume, in the context of the [[Milky Way Galaxy]].]]
Prior to Kepler observation, Kepler-442 had the [[2MASS]] catalogue number 2MASS J19012797+3916482. In the Kepler Input Catalog it has the designation of KIC 4138008, and when it was found to have transiting planet candidates it was given the [[Kepler object of interest]] number of KOI-4742.

Planetary candidates were detected around the star by [[NASA]]'s [[Kepler Mission]], a mission tasked with discovering planets in [[transit method|transit]] around their stars. The transit method that Kepler uses involves detecting dips in brightness in stars. These dips in brightness can be interpreted as planets whose orbits pass in front of their stars from the perspective of [[Earth]], although other phenomenon can also be responsible which is why the term planetary candidate is used.<ref name = "Morton">{{Cite journal | last1=Morton | first1=Timothy | last2=Johnson | first2=John | title=On the Low False Positive Probabilities of Kepler Planet Candidates | journal=The Astrophysical Journal| volume=738 | issue=2 | pages=170 | date=23 August 2011 | doi=10.1088/0004-637X/738/2/170 |arxiv = 1101.5630 |bibcode = 2011ApJ...738..170M | s2cid=35223956 }}</ref>

Following the acceptance of the discovery paper, the Kepler team provided an additional moniker for the system of "Kepler-442".<ref name = "keplernames">{{cite web |url=http://kepler.nasa.gov/Mission/discoveries/ |archive-url=https://web.archive.org/web/20100527104316/http://kepler.nasa.gov/Mission/discoveries/ |url-status=dead |archive-date=27 May 2010 |title=Kepler – Discoveries – Summary Table |author=NASA | date=27 January 2014 |website= |publisher=[[NASA]] |access-date=1 March 2014|author-link=NASA }}</ref> The discoverers referred to the star as Kepler-442, which is the normal procedure for naming the exoplanets discovered by the spacecraft.<ref name="Keplercitepaper"/> Hence, this is the name used by the public to refer to the star and its planet.

Candidate planets that are associated with stars studied by the Kepler Mission are assigned the designations ".01"  etc. after the star's name, in the order of discovery.<ref name = "kepler-catalogue">{{cite web|title=Kepler Input Catalog search result|publisher=[[Space Telescope Science Institute]]|url=http://archive.stsci.edu/kepler/kic10/search.php?kic_kepler_id=9002278&action=Search|access-date=18 April 2013}}</ref> If planet candidates are detected simultaneously, then the ordering follows the order of orbital periods from shortest to longest.<ref name = "kepler-catalogue"/> Following these rules, there was only candidate planet were detected, with an orbital period of 112.3053 days.
 
The designation ''b'' derive from the order of discovery. The designation of ''b'' is given to the first planet orbiting a given star, followed by the other lowercase letters of the alphabet.<ref name="planetnaming">{{cite arXiv |title=On the naming convention used for multiple star systems and extrasolar planets |date=2010 |last1=Hessman |first1=F. V. |last2=Dhillon |first2=V. S. |last3=Winget |first3=D. E. |last4=Schreiber |first4=M. R. |last5=Horne |first5=K. |last6=Marsh |first6=T. R. |last7=Guenther |first7=E. |last8=Schwope |first8=A. |last9=Heber |first9=U. |eprint=1012.0707|class=astro-ph.SR }}</ref> In the case of Kepler-442, there was only one planet detected, so only the letter b is used. The name Kepler-442 derives directly from the fact that the star is the catalogued 442nd star discovered by ''Kepler'' to have confirmed planets.

==Stellar characteristics==
Kepler-442 is a [[K-type main sequence star]] that is approximately 61% the mass of and 60% the radius of the [[Sun]]. It has a temperature of 4402 [[Kelvin scale|K]] and is about 2.9 billion years old, but the margin of error here is quite large.<ref name="Keplercitepaper" /> In comparison, the Sun is about 4.6 billion years old<ref>{{cite web |url=http://www.universetoday.com/18237/how-old-is-the-sun/ |title=How Old is the Sun? |author=Fraser Cain |date=16 September 2008 |website= |publisher=[[Universe Today]] |access-date=19 February 2011}}</ref> and has a temperature of 5778 K.<ref>{{cite web |url=http://www.universetoday.com/18092/temperature-of-the-sun/ |title=Temperature of the Sun |author=Fraser Cain |date=15 September 2008 |website= |publisher=Universe Today |access-date=19 February 2011}}</ref>

The star is somewhat poor in metals, with a [[metallicity]] ([Fe/H]) of about –0.37, or about 43% of the amount of iron and other heavier metals found in the Sun.<ref name="Keplercitepaper"/> The star's luminosity is a bit low for a star like Kepler-442, with a luminosity of around 12% of that of the solar luminosity.<ref name="PHL"/>

Kepler-442 orbits a star with an apparent magnitude of 14.976, rendering it too faint to be visible to the naked eye from Earth. This dimness, as well as its distance from Earth, poses a challenge for direct observation.

==Planetary system==
{{OrbitboxPlanet begin
| name = Kepler-442
| table_ref= <ref name="Keplercitepaper"/>
}}
{{OrbitboxPlanet
| exoplanet = [[Kepler-442b|b]]
| mass_earth = 2.3{{+-|5.9|1.3}}
| period = 112.3053{{+-|0.0024|0.0028}}
| semimajor = 0.409{{+-|0.209|0.060}}
| radius_earth = 1.34{{+-|0.11|0.18}}
| eccentricity  = 0.04{{+-|0.08|0.04}}
| inclination = 89.94{{+-|0.06|0.12}}
}}
{{Orbitbox end}}

The only known planet [[Astronomical transit|transit]]s the star; this means that the planet's orbit appear to cross in front of their star as viewed from the Earth's perspective. Its [[inclination]] relative to Earth's line of sight, or how far above or below the plane of sight it is, vary by less than one degree. This allows direct measurements of the planet's periods and relative diameters (compared to the host star) by monitoring the planet's transit of the star.

Kepler-442b is a super-Earth with a radius 1.34 times that of Earth, and orbits well within the habitable zone. It is likely a [[rocky planet]] due to its radius. According to NASA, it was described as being one of the most [[Earth analog|Earth-like planets]], in terms of size and [[Habitable zone|temperature]], yet found.<ref name="NASA-20150106">{{cite web |last1=Clavin |first1=Whitney |last2=Chou |first2=Felicia |last3=Johnson |first3=Michele |title=NASA's Kepler Marks 1,000th Exoplanet Discovery, Uncovers More Small Worlds in Habitable Zones |url=http://www.jpl.nasa.gov/news/news.php?release=2015-003 |date=6 January 2015 |work=[[NASA]] |access-date=6 January 2015 }}</ref><ref name="TG-20150107-IS">{{cite news |last=Sample |first=Ian |title=Kepler 438b: Most Earth-like planet ever discovered could be home for alien life |url=https://www.theguardian.com/science/2015/jan/06/earth-like-planet-alien-life-kepler-438b |date=7 January 2015 |work=[[The Guardian]] |access-date=7 January 2015 }}</ref> It is just outside of the zone (around 0.362 AU) where tidal forces from its host star would be enough to tidally lock it.<ref name=":0">{{Cite web|url = http://phl.upr.edu/projects/habitable-exoplanets-catalog/results|title = Planetary Habitability Laboratory at University of Puerto Rico|date = |website = |last = |first = |access-date = 2016-07-30|archive-date = 2012-01-08|archive-url = https://web.archive.org/web/20120108040818/http://phl.upr.edu/projects/habitable-exoplanets-catalog/results|url-status = dead}}</ref>

==See also==
* [[Kepler Mission]]
* [[List of planetary systems]]

== Notes ==
{{reflist|group="nb"}}

==References==
{{Reflist|refs=

<ref name="Gaia DR3">{{cite Gaia DR3|2100258047339711488}}</ref>

<ref name="Simbad">{{cite simbad | title=Kepler-442 | accessdate=2020-08-21 }}</ref>

<ref name="FraserCainAgain">{{cite web |url=https://www.universetoday.com/144567/the-perfect-stars-to-search-for-life-on-their-planets/|title=The Perfect Stars to Search for Life On Their Planets |author=Fraser Cain |date=10 January 2020 |website= |publisher=[[Universe Today]] |access-date=23 June 2021}}</ref>

<ref name="ExoplanetNASA">{{cite web |url=https://exoplanets.nasa.gov/news/1620/goldilocks-stars-are-best-places-to-look-for-life/|title=Goldilocks Stars Are Best Places to Look for Life |author= |date=21 September 2020|orig-year=14 January 2020 |website= |publisher=[[NASA]] |access-date=23 June 2021|quote=<span style="font-family:LatinModern;">"Kepler-442 is noteworthy in that this star (spectral classification, K5) hosts what is considered one of the best Goldilocks planets, Kepler-442b, a rocky planet that is a little more than twice Earth's mass. So the Kepler-442 system is a Goldilocks planet hosted by a Goldilocks star!" said [[Edward Guinan|Guinan]].</span>}}</ref>

}}

{{Stars of Lyra}}
{{exoplanets}}
{{extraterrestrial life}}
{{Portal bar|Astronomy|Biology}}
{{Sky|19|01|27.98|+|39|16|48.30}}

[[Category:Kepler-442| ]]
[[Category:Planetary systems with one confirmed planet]]
[[Category:K-type main-sequence stars]]
[[Category:Planetary transit variables]]
[[Category:Lyra]]
[[Category:Kepler objects of interest|4742]]
[[Category:TIC objects]]