View source for Astronomy:Kepler-452b

{{short description|Super-Earth exoplanet orbiting Kepler-452}}
{{Infobox planet
| name                     = Kepler-452b
| image                    = Kepler-452b artist concept.jpg
| caption                  = Artist's impression of Kepler-452b ''(center)'', depicted here as a [[Astronomy:Terrestrial planet|rocky planet]] in the [[Astronomy:Habitable zone|habitable zone]] with extensive cloud cover. The actual appearance of the exoplanet is unknown.
<!-- DISCOVERY           -->
| discoverer               = Kepler Science team
| discovery_site           = ''[[Astronomy:Kepler telescope|Kepler]]''
| discovered               = 23 July 2015 (announced)
| discovery_method         = Transit
<!-- DESIGNATIONS        -->
| alt_names                = KOI-7016.01
<!-- ORBITAL             --> 
| apsis                    = astron
| semimajor                = 1.046{{±|0.019|0.015}}<ref name="NASA-EPA-Kepler452b">{{cite web |title=NASA Exoplanet Archive – Confirmed Planet Overview – Kepler-452b
|url=http://exoplanetarchive.ipac.caltech.edu/cgi-bin/DisplayOverview/nph-DisplayOverview?objname=Kepler-452+b |year=2009 |work=[[Astronomy:NASA Exoplanet Archive|NASA Exoplanet Archive]] |access-date=23 July 2009 }}</ref> [[Astronomy:Astronomical unit|AU]]
| period                   = 384.843{{±|0.007|0.012}}<ref name="NASA-EPA-Kepler452b" /> [[Day|d]]
| inclination              = 89.806{{±|0.134|0.049}}
| star                     = [[Astronomy:Kepler-452|Kepler-452]]
<!-- PHYS CHARS          --> 
| mean_radius              = 1.5{{±|0.32|0.22}}<ref name="NASA-EPA-Kepler452b" /> {{Earth radius|link=y}}
| mass                     = 5 ± 2<ref>{{cite web|url=http://kepler.nasa.gov/news/index.cfm?FuseAction=ShowNews&NewsID=393|archive-url=https://web.archive.org/web/20150815125616/http://kepler.nasa.gov/news/index.cfm?FuseAction=ShowNews&NewsID=393|url-status=dead|archive-date=15 August 2015|title=NASA's Kepler Mission Discovers Bigger, Older Cousin to Earth|work=National Aeronautics and Space Administration|date=23 July 2015|access-date=10 June 2016}}</ref> {{Earth mass|link=y}}
| surface_grav             = 1.9{{±|1.5|1.0}} (est.) [[Physics:G-force|g]]
| single_temperature       = [[Astronomy:Planetary equilibrium temperature|''T''<sub>eq</sub>]]: 265K{{±|15|13}} ({{Convert|265|K|C F}})<ref name="NASA-EPA-Kepler452b" />
<!-- ATMOSPHERE          --> 
<!-- NOTES               --> 
}}
'''Kepler-452b''' (sometimes quoted to be an ''Earth 2.0'' or ''Earth's Cousin''<ref name="RinconP2015">{{cite news |last=Rincon |first=Paul |url=https://www.bbc.com/news/science-environment-33641648 |title='Earth 2.0' found in Nasa Kepler telescope haul |publisher=BBC News |date=23 July 2015 |access-date=24 July 2015 }}</ref><ref name="express.co.uk">[http://www.express.co.uk/news/science/594133/Kepler-452b-How-long-take-humans-reach-Earth-2-could-we-live-there Kepler-452b: How long would it take humans to reach 'Earth 2' and could we live there?]</ref> based on its characteristics; also known by its Kepler Object of Interest designation ''KOI-7016.01'') is a [[Astronomy:Super-Earth|super-Earth]] [[Astronomy:Exoplanet|exoplanet]] orbiting within the inner edge of the [[Astronomy:Habitable zone|habitable zone]] of the sun-like star [[Astronomy:Kepler-452|Kepler-452]] and is the only planet in the system discovered by ''Kepler''. It is located about {{convert|1800|ly|pc}}<ref name=PHL>{{cite web|url=http://phl.upr.edu/projects/habitable-exoplanets-catalog|title=The Habitable Exoplanets Catalog – Planetary Habitability Laboratory @ UPR Arecibo|work=upr.edu}}</ref> from [[Astronomy:Earth|Earth]] in the constellation of [[Astronomy:Cygnus (constellation)|Cygnus]].

Kepler-452b orbits its star at a distance of {{convert|1.04|AU|e6km e6mi|abbr=unit}} from its host star (nearly the same distance as Earth from the Sun), with an orbital period of roughly 385 days, has a mass at least five times that of Earth, and has a radius of around 1.5 times that of Earth. It is the first potentially rocky [[Astronomy:Super-Earth|super-Earth]]<ref name=PHL/> planet discovered orbiting within the [[Astronomy:Circumstellar habitable zone|habitable zone]] of a very sun-like star.<ref name=Chou>{{cite press release|last1=Chou|first1=Felicia|last2=Johnson|first2=Michele|title=NASA's Kepler Mission Discovers Bigger, Older Cousin to Earth|url=http://www.nasa.gov/press-release/nasa-kepler-mission-discovers-bigger-older-cousin-to-earth|access-date=23 July 2015|agency=NASA|date=23 July 2015}}</ref> However, it is unknown if it is entirely habitable, as it is receiving slightly more energy than Earth and could be subjected to a [[Earth:Runaway greenhouse effect|runaway greenhouse effect]].

The [[Astronomy:Kepler space telescope|''Kepler'']] [[Astronomy:Space telescope|space telescope]] identified the exoplanet, and its discovery was announced by [[Organization:NASA|NASA]] on 23 July 2015.<ref name=Jenkins2015>{{cite journal| last1=Jenkins| first1=Jon M.| last2=Twicken| first2=Joseph D.| last3=Batalha|first3=Natalie M.| last4=Caldwell| first4=Douglas A.| last5=Cochran| first5=William D.| last6=Endl| first6=Michael| last7=Latham| first7=David W.| last8=Esquerdo| first8=Gilbert A.|last9=Seader|first9=Shawn|last10=Bieryla|first10=Allyson|last11=Petigura|first11=Erik|last12=Ciardi|first12=David R.|last13=Marcy|first13=Geoffrey W.|last14=Isaacson|first14=Howard|last15=Huber|first15=Daniel|last16=Rowe|first16=Jason F.|last17=Torres|first17=Guillermo|last18=Bryson|first18=Stephen T.|last19=Buchhave|first19=Lars|last20=Ramirez|first20=Ivan|last21=Wolfgang|first21=Angie|last22=Li|first22=Jie|last23=Campbell|first23=Jennifer R.|last24=Tenenbaum|first24=Peter|last25=Sanderfer|first25=Dwight|last26=Henze|first26=Christopher E.|last27=Catanzarite|first27=Joseph H.|last28=Gilliland|first28=Ronald L.|last29=Borucki|first29=William J.|display-authors=3| title=Discovery and Validation of Kepler-452b: A 1.6 R<sub>🜨</sub> Super Earth Exoplanet in the Habitable Zone of a G2 Star| journal=The Astronomical Journal| date=23 July 2015| volume=150| issue=2| page=56| issn=1538-3881|doi=10.1088/0004-6256/150/2/56| url=http://www.nasa.gov/sites/default/files/atoms/files/ms-r1b.pdf|access-date=24 July 2015|arxiv = 1507.06723 |bibcode = 2015AJ....150...56J | s2cid=26447864}}</ref> The planet is about {{convert|1,800|ly|pc}} away from the [[Astronomy:Solar System|Solar System]]. At the speed of the ''[[Astronomy:New Horizons|New Horizons]]'' [[Engineering:Spacecraft|spacecraft]], at about {{convert|59,000|km/h|m/s mph|abbr=on}}, it would take approximately 30 million years to get there.<ref name="bno">{{cite web |url=http://bnonews.com/news/index.php/news/id961 |title=NASA telescope discovers Earth-like planet in star's 'habitable zone |date=23 July 2015 |work=BNO News |access-date=23 July 2015 |archive-date=4 March 2016 |archive-url=https://web.archive.org/web/20160304042706/http://bnonews.com/news/index.php/news/id961 |url-status=dead }}</ref>

==Physical characteristics==
===Mass, radius and temperature=== 
[[File:Kepler-452b and Earth Size.jpg|thumb|300px|Size comparison between Kepler-452b ''(right)'' and Earth ''(left)'', along with the similarities of their parent stars.]]
Kepler-452b has a probable mass five times that of Earth, and its surface gravity is nearly twice as much as Earth's, though calculations of mass for exoplanets are only rough estimates.<ref name=Feltman /> If it is a [[Astronomy:Terrestrial planet|terrestrial planet]], it is most likely a [[Astronomy:Super-Earth|super-Earth]] with many active volcanoes due to its higher mass and density. The clouds on the planet would be thick and misty, covering much of the surface as viewed from space.

The planet takes 385 Earth days to orbit its star.<ref name=Overbye>{{cite news|last1=Overbye|first1=Dennis|title=Kepler Data Reveals What Might Be Best 'Goldilocks' Planet Yet|url=https://www.nytimes.com/2015/07/24/science/space/kepler-data-reveals-what-might-be-best-goldilocks-planet-yet.html|access-date=23 July 2015|work={{wipe|The New York Times}}|date=23 July 2015}}</ref> Its radius is 50% larger than [[Astronomy:Earth|Earth]]'s, and lies within the conservative [[Astronomy:Circumstellar habitable zone|habitable zone]] of its parent star.<ref name=Feltman>{{cite news|last1=Feltman|first1=Rachel|title=Scientists discover 12 new potential Earth-like planets|url=https://www.washingtonpost.com/news/speaking-of-science/wp/2015/07/23/scientists-discover-12-new-potential-earth-like-planets/|access-date=23 July 2015|newspaper={{wipe|The Washington Post}}|date=23 July 2015}}</ref><ref name=Witze>{{cite news|last1=Witze|first1=Alexandra|title=NASA spies Earth-sized exoplanet orbiting Sun-like star|url=http://www.nature.com/news/nasa-spies-earth-sized-exoplanet-orbiting-sun-like-star-1.18048|access-date=23 July 2015|work=Nature|date=23 July 2015}}</ref> It has an equilibrium temperature of {{convert|265|K|C F}}, a little warmer than Earth.

===Host star===
{{main|Astronomy:Kepler-452}}
The host star, [[Astronomy:Kepler-452|Kepler-452]], is a [[Astronomy:Stellar classification#Class G|G-type]] and has about the same mass as the sun, only 3.7% more massive and 11% larger. It has a surface temperature of 5757 [[Kelvin|K]], nearly the same as the Sun, which has a surface 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 |publisher=Universe Today |access-date=19 February 2011}}</ref>

The star's age is estimated to be about 6 billion years old, about 1.5 billion years older than the Sun, which is estimated to have existed for 4.6 billion years. Kepler-452b has been in Kepler-452's habitable zone for most of its existence, a duration just over six billion years.<ref name=":022">{{Cite book |last1=Bohan |first1=Elise |url=https://www.worldcat.org/oclc/940282526 |title=Big History |last2=Dinwiddie |first2=Robert |last3=Challoner |first3=Jack |last4=Stuart |first4=Colin |last5=Harvey |first5=Derek |last6=Wragg-Sykes |first6=Rebecca |last7=Chrisp |first7=Peter |last8=Hubbard |first8=Ben |last9=Parker |first9=Phillip |collaboration=Writers |date=February 2016 |publisher=DK |others=Foreword by David Christian |isbn=978-1-4654-5443-0 |edition=1st American |location={{wipe|New York City}} |pages=77 |oclc=940282526 |author-link7=Peter Chrisp}}</ref>

From the surface of Kepler-452b, its star would look almost identical to the [[Astronomy:Sun|Sun]] as viewed from the Earth.<ref>NASA Kepler press conference. 23 July 2015.</ref>

The star's [[Astronomy:Apparent magnitude|apparent magnitude]], or how bright it appears from Earth's perspective, is 13.426; therefore, it is too dim to be seen with the naked eye.

===Orbit===
Kepler-452b orbits its host star with an orbital period of 385 days and an orbital radius of about 1.04 [[Astronomy:Astronomical unit|AU]], nearly the same as Earth's (1 AU). Kepler-452b is most likely not tidally locked and has a circular orbit. Its host star, Kepler-452, is about 20% more luminous than the Sun (L = 1.2 {{solar luminosity}}).

==Potential habitability==
[[File:Kepler452b-Earth-SurfaceTemp-vs-Energy-20150723.gif|thumb|left|275px|Comparison of Kepler-452b and related exoplanets with Earth.]]
It is not known if Kepler-452b is a [[Astronomy:Terrestrial planet|rocky planet]]<ref name="RinconP2015" /> but based on its small radius, Kepler-452b is likely to be rocky.<ref name=Jenkins2015 /> It is not clear if Kepler-452b offers habitable environments. It orbits a G2V-type star, like the Sun, which is 20% more luminous, with nearly the same temperature and mass.<ref name=Overbye /> However, the star is roughly 6 billion years old, making it 1.5 billion years older than the Sun. At this point in its star's [[Astronomy:Stellar evolution|evolution]], Kepler-452b is currently receiving 10% more energy from its parent star than Earth is currently receiving from the Sun.<ref name=Chou /> If Kepler-452b is a rocky planet, it may be subject to a [[Earth:Runaway greenhouse effect|runaway greenhouse effect]] similar to that seen on [[Astronomy:Venus|Venus]].<ref name=Lugmayr>{{cite news|last1=Lugmayr|first1=Luigi|title=Kepler-452b details unveiled|url=http://www.i4u.com/2015/07/93538/kepler-452b-details-unveiled|access-date=23 July 2015|agency=I4U News|date=23 July 2015}}</ref>

==="Delayed" runaway greenhouse effect===
However, due to the planet Kepler-452b being 50 percent bigger in terms of size, it is likely to have an estimated mass of 5 {{earth mass}}, which could allow it to hold on to any oceans it may have for a longer period, preventing Kepler-452b from succumbing to runaway greenhouse effect for another 500 million years.<ref name=Lugmayr/> This, in turn, would be accompanied by the [[Chemistry:Carbonate–silicate cycle|carbonate–silicate cycle]] being "buffered", extending its lifetime due to increased volcanic activity on Kepler-452b.<ref name=Kep452bAdvancedEarth2.0>{{cite web|url=https://gizmodo.com/is-earths-closest-cousin-a-dying-planet-1720434455|title=Is Earth's Closest Cousin A Dying Planet?|work=Gizmodo.com|date=30 July 2015|access-date=24 May 2016}}</ref> This could allow any potential life on the surface to inhabit the planet for another 500–900 million years before the habitable zone is pushed beyond Kepler-452b's orbit.

==Discovery and follow-up studies==
In 2009, [[Organization:NASA|NASA]]'s [[Engineering:Kepler (spacecraft)|Kepler]] spacecraft was observing stars on its [[Physics:Photometer|photometer]], the instrument it uses to detect transit events, in which a planet crosses in front of and dims its host star for a brief and roughly regular time. In this last test, Kepler observed {{val|50,000}} stars in the [[Astronomy:Kepler Input Catalog|Kepler Input Catalog]], including Kepler-452; the preliminary light curves were sent to the Kepler science team for analysis, who chose obvious planetary companions from the bunch for follow-up by other telescopes. Observations for the potential exoplanet candidates took place between 13 May 2009 and 17 March 2012. Kepler-452b exhibited a transit that occurred roughly every 385 days, and it was eventually concluded that a planetary body was responsible. The discovery was announced by NASA on 23 July 2015.<ref name=Jenkins2015/>

At a distance of nearly {{convert|550|pc|ly|disp=flip}}, Kepler-452b is too remote for current telescopes or the next generation of planned telescopes to determine its true mass or whether it has an atmosphere. The Kepler spacecraft focused on a single small region of the sky but next-generation planet-hunting space telescopes, such as [[Astronomy:Transiting Exoplanet Survey Satellite|TESS]] and [[Astronomy:CHEOPS|CHEOPS]], will examine nearby stars throughout the sky with follow up studies planned for these closer exoplanets by the [[Astronomy:James Webb Space Telescope|James Webb Space Telescope]] and future large ground-based telescopes to analyze their atmospheres, determine masses, and infer compositions.

A study in 2018 by Mullally et al. claimed that statistically, Kepler-452b has not been proven to exist and must still be considered a candidate.<ref>''Kepler's Earth-like Planets Should Not Be Confirmed without Independent Detection: The Case Of Kepler-452b'' Fergal Mullally, Susan E. Thompson, Jeffrey L. Coughlin, Christopher J. Burke, and Jason F. Rowe, 2 April 2018. Available at {{ArXiv|1803.11307}}, Accessed 3 April 2018.</ref>

===SETI targeting===
Scientists with the SETI (Search for Extraterrestrial Intelligence Institute) have already begun targeting Kepler-452b, the first near-Earth-size world found in the [[Astronomy:Habitable zone|habitable zone]] of a Sun-like star.<ref name="space.com">[http://www.space.com/30114-seti-alien-life-kepler-452b-earth-cousin.html SETI Targets Kepler-452b, Earth's 'Cousin,' in Search for Alien Life]</ref> SETI Institute researchers are using the [[Astronomy:Allen Telescope Array|Allen Telescope Array]], a collection of 6-meter (20 feet) telescopes in the Cascade Mountains of California, to scan for radio transmissions from Kepler-452b. As of July 2015, the array has scanned the exoplanet on over 2 billion frequency bands, with no result. The telescopes will continue to scan over a total of 9 billion channels, searching for alien radio analysis.<ref name="space.com" />

==Observation and exploration==
Kepler-452b is {{convert|1,800|ly|pc|abbr=off}} from Earth. The fastest current spacecraft, the ''[[Astronomy:New Horizons|New Horizons]]'' uncrewed probe that passed [[Astronomy:Pluto|Pluto]] in July 2015, travels at just {{convert|56,628|km/h|m/s mph AU/h|abbr=on}}.<ref name="express.co.uk" /> At that speed, it would take a spacecraft about 26 million years to reach Kepler-452b from Earth, if it were going in that direction.<ref name="express.co.uk" />

{| class="wikitable" style="margin:0.5em auto; width:450px; align=right"
! [[Astronomy:Exoplanet|Notable Exoplanets]] – [[Engineering:Kepler (spacecraft)|Kepler Space Telescope]] 
|-
| style="font-size:88%" | [[File:PIA19827-Kepler-SmallPlanets-HabitableZone-20150723.jpg|600px]]
{{center|Comparison of small planets found by ''[[Engineering:Kepler (spacecraft)|Kepler]]'' in the [[Astronomy:Habitable zone|habitable zone]] of their host stars.}}
|}

==Gallery==
{{Gallery |align=center |width=450
|File:Kepler-452b System.jpg|{{center|{{small|A diagram of the orbit of Kepler-452b within the Kepler-452 system, as compared to the inner Solar System and Kepler-186 system, and their respective projected habitable zones.}}}}
|title=}}

==See also==
* [[Astronomy:List of largest exoplanets|List of largest exoplanets]]
* [[Astronomy:List of potentially habitable exoplanets|List of potentially habitable exoplanets]]
* [[Astronomy:Superhabitable planet|Superhabitable planet]]

==References==
{{Reflist|refs=

}}

==External links==
* [https://www.nasa.gov/mission_pages/kepler/overview/index.html NASA – Mission overview]
* [https://web.archive.org/web/20100527104316/http://kepler.nasa.gov/Mission/discoveries/ NASA – Kepler Discoveries – Summary Table]
* [http://phl.upr.edu/projects/habitable-exoplanets-catalog Habitable Exoplanets Catalog] at UPR-Arecibo.
* [http://www.nasa.gov/sites/default/files/atoms/files/ms-r1b.pdf Discovery and Validation of Kepler-452b: A 1.6-R<sub>🜨</sub> Super-Earth Exoplanet in the Habitable Zone of a G2 Star]

{{Exoplanet}}
{{Astrobiology}}
{{Extraterrestrial life}}
{{2015 in space}}
{{Sky|19|44|00.89|+|44|16|39.2|1400}}

[[Category:Super-Earths in the habitable zone]]
[[Category:Terrestrial planets]]
[[Category:Exoplanets in the habitable zone]]
[[Category:Super-Earths]]
[[Category:Transiting exoplanets]]
[[Category:Cygnus (constellation)]]
[[Category:Exoplanet candidates]]

{{Sourceattribution|Kepler-452b}}