View source for Astronomy:HD 17156 c

{{Infobox planet
| name                     = HD 17156 c
<!-- DISCOVERY           -->
| discoverer               = Short ''et al.''
| discovery_site           = {{flag|United States}}
| discovered               = 20 March 2008
| discovery_method         = Planetary perturbation
<!-- DESIGNATIONS        -->
<!-- ORBITAL             --> 
| apsis                    = astron
| semimajor                = {{convert|0.481|±|0.001|AU|km|abbr=on}}
| eccentricity             = 0.136±0.005
| period                   = 111.314±3 [[Day|d]]
| star                     = [[Astronomy:HD 17156|HD 17156]]
<!-- PHYS CHARS          --> 
| mass                     = 0.063 ± 0.007 {{Jupiter mass|link=y}}<br>(20 ± 2.2 {{Earth mass|link=y}})
<!-- ATMOSPHERE          --> 
<!-- NOTES               --> 
}}
'''HD 17156 c''' is a plausible extrasolar planet approximately 255 [[Astronomy:Light-year|light-year]]s away in the [[Astronomy:Constellation|constellation]] of [[Astronomy:Cassiopeia (constellation)|Cassiopeia]].  The planet is thought to be orbiting the [[Astronomy:Yellow giant|yellow giant]] [[Astronomy:Star|star]] [[Astronomy:HD 17156|HD 17156]].  This planet has a [[Physics:Mass|mass]] of 0.063 [[Astronomy:Jupiter mass|Jupiter mass]] (or 20 [[Astronomy:Earth mass|Earth mass]]es) and takes about 111.314 days or 0.305 year to orbit the star, classifying the planet as a cool Neptunian planet.  This put it in the distance of 0.481 [[Astronomy:Astronomical unit|astronomical unit]]s or 72.0 gigameters with a moderate eccentricity.

The two planets "exchange angular momentum in a 5:1 mean motion resonance".

This planet was discovered on the [[Astronomy:March equinox|vernal equinox]] of 2008 by analyzing perturbations with the inner planet [[Astronomy:HD 17156 b|HD 17156 b]]. The paper was submitted to ''Astrophysical Journal Letters'' 20 March and revised 14 June.

== See also ==

* [[Astronomy:HD 17156 b|HD 17156 b]]

== References ==
* {{cite arXiv |arxiv=0803.2935 |author1=Donald Short |author2=William F. Welsh |author3=Jerome A. Orosz |author4=Gur Windmiller |title=Orbital Dynamics Of A Second Planet In HD17156 |date=2008 |volume= |issue= |pages= |<!--bibcode = 2008arXiv0803.2935S--> }}

{{Sky|02|49|44.49|+|71|45|11.64|255.19}}

[[Category:Cassiopeia (constellation)]]
[[Category:Exoplanet candidates]]
[[Category:Giant planets]]



{{Sourceattribution|HD 17156 c|1}}