View source for HD 219134 g

{{Short description|Unconfirmed exoplanet orbiting HD 219134}}
{{Infobox planet
| name                     = [[Henry Draper Catalogue|HD]] 219134 g
<!-- DISCOVERY           -->
| discoverer               = [[HARPS-N]]
| discovery_site           = [[La Palma]], [[Canary Islands]]
| discovered               = 2015 November 17
| discovery_method         = [[radial velocity method]]
<!-- DESIGNATIONS        -->
<!-- ORBITAL             --> 
| apsis                    = astron
| semimajor                = {{val|0.3753|0.0004|ul=AU}},<ref name="Vogt2015"/> {{val|0.603|0.001|ul=AU}}<ref name="Hirsch2020"/>
| eccentricity             = 0,<ref name="Vogt2015"/> {{val|0.16|0.1}}<ref name="Hirsch2020"/>
| period                   = {{val|94.2|0.2|ul=d}},<ref name="Vogt2015"/> {{val|192.0|0.5|0.4|ul=d}}<ref name="Hirsch2020"/>
| inclination              = 
| arg_peri                 = {{val|0|u=deg}},<ref name="Vogt2015"/> {{val|-0.4|0.6|ul=rad}}<ref name="Hirsch2020"/>
| semi-amplitude           = {{val|1.8|0.2|ul=m/s}},<ref name="Vogt2015"/> {{val|2.0|0.2|ul=m/s}}<ref name="Hirsch2020"/>
| star                     = [[HD 219134]]
<!-- PHYS CHARS          --> 
| mean_radius              = 
| mass                     = {{val|10.8|1.3|p=≥|ul=Earth mass}},<ref name="Vogt2015"/> {{val|15.3|1.6|p=≥|ul=Earth mass}}<ref name="Hirsch2020"/>
| single_temperature       = {{convert|298|K|C F}}<ref name=ExoplanetsCalculator>{{cite web
 | url=http://phl.upr.edu/projects/habitable-exoplanets-catalog/calculators
 | title=HEC: Exoplanets Calculator
 | work=phl.upr.edu
 | access-date=2017-12-24
 | archive-date=2017-08-24
 | archive-url=https://web.archive.org/web/20170824164045/http://phl.upr.edu/projects/habitable-exoplanets-catalog/calculators
 | url-status=dead
 }}</ref>
<!-- ATMOSPHERE          --> 
<!-- NOTES               --> 
}}
'''HD 219134 g''', also known as '''HR 8832 g''', is an unconfirmed<ref name="Hirsch2020"/> [[exoplanet]] orbiting around the [[K-type main sequence star|K-type star]] [[HD 219134]] in the constellation of [[Cassiopeia (constellation)|Cassiopeia]]. It has a [[minimum mass]] of 11 or 15 Earth masses, suggesting that it is likely a [[Neptune]]-like ice giant. Unlike [[HD 219134 b]] and [[HD 219134 c]] it is not observed to transit and thus its radius and density are unknown. If it has an Earth-like composition, it would have a radius 1.9 times that of Earth.{{citation needed|date=December 2022}} However, since it is probably a Neptune-like planet, it is likely larger.

==Characteristics==

===Mass, Radius, and Temperature===

HD 219134 g is a sub-Neptune-mass exoplanet with a minimum mass of {{Earth mass|10.8}} and an unknown radius, as it is not known to transit.<ref name="NASAExoplanetArchive"/> However, due to the high metal content of the host star, the planet might not be an ice giant.{{citation needed|date=December 2022}} For a rock-iron composition, HD 219134 g would be about 1.9 {{Earth radius}}, which seems unlikely for a planet of this mass. A more plausible rock-water composition would put the planet at about 2.4 {{Earth radius}}.{{citation needed|date=December 2022}} Assuming an albedo of 0.3, it has an [[equilibrium temperature]] of {{convert|298|K|C F}},<ref name=ExoplanetsCalculator/> but with an atmosphere it is likely to have a surface temperature much higher, that is if it has a rocky surface. So, it is rather unlikely to be habitable.

===Orbit===

HD 219134 g was initially estimated to take about 94.2 days to orbits its star at a distance of 0.3753 [[Astronomical unit|AU]].<ref name="Vogt2015"/> This is comparable to [[Mercury (planet)|Mercury's]] orbit of 88 days at about 0.38 AU. However, due to the lower luminosity of the host star, HD 219134 g is closer to [[Venus]]' situation. The eccentricity of the planet's orbit is believed to be close to zero, indicating a very circular orbit.<ref name="NASAExoplanetArchive"/>

However, a 2020 study did not find evidence of a radial velocity signal at this period, but instead found a period of 192 days, corresponding to an orbital distance of 0.603 AU.<ref name="Hirsch2020"/>

===Host Star===

The planet HD 219134 g orbits the K3V orange dwarf [[HD 219134]], also known as HR 8832. It is 79% the radius and 80% the mass of the Sun with 26% the luminosity. It has a temperature of 4699 K and is around 11 billion years old.<ref name="NASAExoplanetArchive"/> For comparison, the Sun has a temperature of 5778 K and is 4.55 billion years old.

The apparent magnitude of the star, or how bright it appears from Earth, is around 5. Therefore, it is just visible to the unaided eye to most observers.

==Habitability==

The habitable zone for this star, as defined by Kopparapu et al. 2014,<ref name=kopparapu-2014/> for a 5 Earth mass planet, would be between 0.499 AU and 0.947 AU.{{#tag:ref|<math>\scriptstyle S_{eff_{\ast}}= S_{eff_{\odot}} + aT_{\ast} + bT_{\ast}^2 + cT_{\ast}^3  + dT_{\ast}^4</math> <ref name=kopparapu-2014/> when used to calculate the stellar flux reaching the outer atmosphere of a 5 mass Earth-like planet orbiting HD 219134 at the Inner Habitable Zone edge - the Runaway Greenhouse limit gives a <math>\scriptstyle S_{eff_{\ast}}</math> of 1.0615 or 106.15% the stellar flux reaching the top of Earth's atmosphere. By applying the previously calculated stellar flux and the known 26.46% luminosity of HD 219134 into the equation, <math>\scriptstyle {d = {\left(\frac{{L_{\ast}}/{L_{\odot}}}{S_{eff_{\ast}}} \right)^{0.5} AU}}</math>,<ref name=kopparapu-2014/><ref name=kopparapu-2013/> the distance of the Inner HZ - Runaway Greenhouse limit from HD 219134 can be calculated as <math>\scriptstyle{0.499 AU}</math>.|group="note"|name=maximum greenhouse}}<ref name=Habitable_Zone_Calculator>{{cite web
 | website=Department of Geosciences, Penn State
 | url=http://www3.geosc.psu.edu/~ruk15/planets/
 | title=Habitable Zone Calculator
 | access-date=2018-12-30
}}</ref> HD 219134 g may orbit slightly interior to the inner edge of the habitable zone based on its initially published parameters,<ref name="Vogt2015" /> or may orbit within the habitable zone based on a more recent estimated orbital period of 192 days and semi-major axis of 0.603 AU.<ref name="Hirsch2020"/> This planet is significantly more massive than Earth and therefore it likely retains a dense atmosphere, comparable to the Solar System's [[ice giant]]s.

==References==
{{Reflist|refs=

<ref name=kopparapu-2013>{{cite journal | title=Habitable Zones Around Main-sequence Stars: New Estimates| last1=Kopparapu| first1= R. K.| last2=Ramirez | first2= R. | last3=Kasting | first3= J.F. | last4=Eymet| first4=V. | last5=Robinson | first5= T. D. | last6=Mahadevan | first6= S. | last7=Terrien | first7=R.C. | last8=Domagal-Goldman | first8=S. | last9=Meadows| first10= V. | last10=Deshpande | first9= R. | journal=[[The Astrophysical Journal]] |date=March 2013| volume=765 | issue=2 | doi=10.1088/0004-637X/765/2/131 | arxiv=1301.6674 | pages=16 |bibcode = 2013ApJ...765..131K | bibcode-access=free | doi-access=free }}</ref>

<ref name=kopparapu-2014>{{cite journal | title=Habitable Zones Around Main-Sequence Stars: Dependence on Planetary Mass | last1=Kopparapu| first1= Ravi Kumar | last2=Ramirez | first2= Ramses M. | last3=SchottelKotte | first3= James | last4=Kasting | first4=James F. | last5=Domagal-Goldman | first5= Shawn | last6=Eymet | first6= Vincent | journal=[[The Astrophysical Journal Letters]] |date=15 May 2014 | volume=787 | issue=2 | doi=10.1088/2041-8205/787/2/L29 | arxiv=1404.5292 | pages=6 | bibcode = 2014ApJ...787L..29K | bibcode-access=free | doi-access=free }}</ref>

<ref name=NASAExoplanetArchive>{{cite web
 | url=https://exoplanetarchive.ipac.caltech.edu/cgi-bin/DisplayOverview/nph-DisplayOverview?objname=HD+219134+g&type=CONFIRMED_PLANET
 | title=HD 219134 g
 | work=exoplanetarchive.ipac.caltech.edu
 | access-date=2017-12-24
}}</ref>

<ref name="Vogt2015">{{cite journal |arxiv=1509.07912 |last1=Vogt |first1=Steven S. |display-authors=etal |title=Six Planets Orbiting HD 219134 |date=November 2015 |doi=10.1088/0004-637X/814/1/12 |volume=814 |issue=1 |journal=[[The Astrophysical Journal]] |page=12 |bibcode=2015ApJ...814...12V|s2cid=45438051 }}</ref>

<ref name="Hirsch2020">{{citation
 |title=Understanding the Impacts of Stellar Companions on Planet Formation and Evolution: A Survey of Stellar and Planetary Companions within 25 pc
 | display-authors=1 | last1=Hirsch | first1=Lea A.
 | last2=Rosenthal | first2=Lee | last3=Fulton | first3=Benjamin J.
 | last4=Howard | first4=Andrew W. | last5=Ciardi | first5=David R.
 | last6=Marcy | first6=Geoffrey W. | last7=Nielsen | first7=Eric L.
 | last8=Petigura | first8=Erik A. | last9=de Rosa | first9=Robert J.
 | last10=Isaacson | first10=Howard | last11=Weiss | first11=Lauren M.
 | last12=Sinukoff | first12=Evan | last13=Macintosh | first13=Bruce
 | journal=[[The Astronomical Journal]] | year=2021 | volume=161 | issue=3 | page=134 | postscript=.
 | doi=10.3847/1538-3881/abd639 | arxiv=2012.09190 | bibcode=2021AJ....161..134H | s2cid=229297873 | doi-access=free }}</ref>

}}

== Notes ==
{{reflist|group=note|refs=

}}

{{HD 219134}}
{{2015 in space}}

[[Category:Cassiopeia (constellation)]]
[[Category:Exoplanets discovered in 2015]]
[[Category:Exoplanets detected by radial velocity]]