View source for Astronomy:HIP 57274 d

{{Short description|Exoplanet in the constellation Cetus}}
{{Infobox planet
| name                     = HIP 57274 d
<!-- DISCOVERY           -->
| discoverer               = Fischer ''et al''.
| discovered               = 28 December 2011
| discovery_method         = radial velocity
<!-- DESIGNATIONS        -->
<!-- ORBITAL             --> 
| apsis                    = astron
| semimajor                = {{convert|1.01|AU|km|abbr=on}}
| eccentricity             = 0.27 (± 0.05)<ref name="Extrasolar">{{cite web |title=Planet HIP 57274 d |url=https://exoplanet.eu/catalog/hip_57274_d--995/ |work=[[Astronomy:Extrasolar Planets Encyclopaedia|Extrasolar Planets Encyclopaedia]] |access-date=17 July 2015}}</ref>
| period                   = 413.7 (± 8.5)<ref name="Extrasolar"/> [[Day|d]]
| star                     = [[Astronomy:HIP 57274|HIP 57274]]
<!-- PHYS CHARS          --> 
| mean_radius              = ~9 {{Earth radius|link=y}}
| mass                     = 0.527 (± 0.025)<ref name="Extrasolar"/> {{Jupiter mass|link=y}}<br />(167.5 {{Earth mass|link=y}})
| single_temperature       = {{convert|167|K|C F}}<ref>{{cite web | url=http://www.openexoplanetcatalogue.com/planet/HIP%2057274%20d/ | title=Open Exoplanet Catalogue - HIP 57274 D }}</ref>
<!-- ATMOSPHERE          --> 
<!-- NOTES               --> 
}}
'''HIP 57274 d''' is an [[Astronomy:Exoplanet|exoplanet]] orbiting the K-type main sequence star [[Astronomy:HIP 57274|HIP 57274]] about 84.5 [[Astronomy:Light-year|light-year]]s (26 [[Astronomy:Parsec|parsec]]s, or nearly {{val|8.022|e=16}} km) from [[Astronomy:Earth|Earth]] in the [[Astronomy:Constellation|constellation]] Cetus. It orbits within the outer part of its star's [[Astronomy:Habitable zone|habitable zone]], at a distance of 1.01 [[Astronomy:Astronomical unit|AU]]. The exoplanet was found by using the [[Astronomy:Doppler spectroscopy|radial velocity method]], from [[Astronomy:Radial velocity|radial-velocity]] measurements via observation of Doppler shifts in the [[Spectrum|spectrum]] of the [[Astronomy:Planet|planet's]] parent star.

== Characteristics ==

===Mass, radius and temperature===
HIP 57274 d is a [[Astronomy:Gas giant|gas giant]], a planet that has a radius and mass close to that of the gas giants [[Astronomy:Jupiter|Jupiter]] and [[Astronomy:Saturn|Saturn]]. It has a temperature of {{convert|167|K|C F}}. It has an estimated mass of around 0.527 {{Jupiter mass}} (167 {{Earth mass}}), and a potential radius of around 9 {{Earth radius}} based on its mass, since it is slightly more massive than Saturn.

===Host star===
The planet orbits a ([[Astronomy:Stellar classification#Class K|K-type]]) star named [[Astronomy:HIP 57274|HIP 57274]], orbited by a total of three planets. The star has a mass of 0.73 {{Solar mass}} and a radius of 0.68 {{Solar radius}}. It has a surface temperature of 4640 [[Kelvin|K]] and is 7 billion years old. 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 |publisher=Universe Today |accessdate=19 February 2011}}</ref> and 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=September 15, 2008 |publisher=Universe Today |accessdate=19 February 2011}}</ref>

The star's [[Astronomy:Apparent magnitude|apparent magnitude]], or how bright it appears from Earth's perspective, is 8.96. Therefore, HIP 57274 is too dim to be seen with the naked eye, but can be seen with good binoculars.

=== Orbit ===

HIP 57274 d orbits its star every 432 days at a distance of 1.01 [[Astronomy:Astronomical unit|AU]]. This is very similar to that of [[Astronomy:Earth|Earth]]'s orbital period and distance.

== Habitability ==
HIP 57274 d resides in the outer part of  circumstellar [[Astronomy:Habitable zone|habitable zone]] of the parent star. The exoplanet, with a mass of 0.527 {{Jupiter radius}}, is too massive to be rocky, and because of this the planet itself may not be habitable. Hypothetically, large enough moons, with a sufficient atmosphere and pressure, may be able to support liquid water and potentially life.

For a stable orbit the ratio between the moon's [[Astronomy:Orbital period|orbital period]] ''P''<sub>s</sub> around its primary and that of the primary around its star ''P''<sub>p</sub> must be &lt; 1/9, e.g. if a planet takes 90 days to orbit its star, the maximum stable orbit for a moon of that planet is less than 10 days.<ref name=Kipping_2009a>{{cite journal| last=Kipping| first=David| title=Transit timing effects due to an exomoon| journal=Monthly Notices of the Royal Astronomical Society| year=2009| volume=392| issue=1| pages=181–189| doi=10.1111/j.1365-2966.2008.13999.x| bibcode = 2009MNRAS.392..181K |arxiv = 0810.2243| s2cid=14754293}}</ref><ref name="Heller2012">{{cite journal| last1=Heller| first1=R.| title=Exomoon habitability constrained by energy flux and orbital stability| journal=Astronomy & Astrophysics| volume=545| year=2012| pages=L8| issn=0004-6361| doi=10.1051/0004-6361/201220003| arxiv = 1209.0050 |bibcode = 2012A&A...545L...8H | s2cid=118458061}}</ref> Simulations suggest that a moon with an orbital period less than about 45 to 60 days will remain safely bound to a massive giant planet or [[Astronomy:Brown dwarf|brown dwarf]] that orbits 1 [[Astronomy:Astronomical unit|AU]] from a Sun-like star.<ref name="skyandtelescope">{{cite web| url=http://www.skyandtelescope.com/resources/seti/3304591.html?showAll=y&c=y| publisher=SkyandTelescope.com| title=Habitable Moons:What does it take for a moon — or any world — to support life?| author=Andrew J. LePage| accessdate=2011-07-11| archive-date=2012-04-06| archive-url=https://web.archive.org/web/20120406095618/http://www.skyandtelescope.com/resources/seti/3304591.html?showAll=y&c=y| url-status=dead}}</ref> In the case of HIP 57274 d, the moon's orbit would have to be roughly 40 days to support a stable orbit.

Tidal effects could also allow the moon to sustain [[Earth:Plate tectonics|plate tectonics]], which would cause volcanic activity to regulate the moon's temperature<ref name=volcanoes-climate>{{cite web| last=Glatzmaier| first=Gary A.| title=How Volcanoes Work – Volcano Climate Effects| url=http://www.geology.sdsu.edu/how_volcanoes_work/climate_effects.html| accessdate=29 February 2012| archive-date=23 April 2011| archive-url=https://web.archive.org/web/20110423214804/http://www.geology.sdsu.edu/how_volcanoes_work/climate_effects.html| url-status=dead}}</ref><ref name=nasa-io>{{cite web| title=Solar System Exploration: Io| url=http://solarsystem.nasa.gov/planets/profile.cfm?Object=Io| archive-url=https://web.archive.org/web/20031216112404/http://solarsystem.nasa.gov/planets/profile.cfm?Object=Io| url-status=dead| archive-date=16 December 2003| work=Solar System Exploration| publisher=[[Organization:NASA|NASA]]| accessdate=29 February 2012}}</ref> and create a [[Physics:Dynamo theory|geodynamo effect]] which would give the satellite a strong [[Physics:Magnetic field|magnetic field]].<ref name=hyperphysics-geodynamo>{{cite web| last=Nave| first=R.| title=Magnetic Field of the Earth| url=http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magearth.html| accessdate=29 February 2012}}</ref>

To support an Earth-like atmosphere for about 4.6 billion years (the age of the Earth), the moon would have to have a Mars-like density and at least a mass of 0.07 {{Earth mass}}.<ref>{{cite web| url=http://www.xs4all.nl/~carlkop/habit.html|title=In Search Of Habitable Moons| publisher=[[Organization:Pennsylvania State University|Pennsylvania State University]]| accessdate=2011-07-11}}</ref> One way to decrease loss from [[Physics:Sputtering|sputtering]] is for the moon to have a strong [[Physics:Magnetic field|magnetic field]] that can deflect [[Astronomy:Stellar wind|stellar wind]] and radiation belts. NASA's [[Engineering:Galileo (spacecraft)|Galileo's]] measurements hints large moons can have magnetic fields; it found that [[Astronomy:Jupiter|Jupiter]]'s moon [[Astronomy:Ganymede (moon)|Ganymede]] has its own magnetosphere, even though its mass is only 0.025 {{Earth mass}}.<ref name="skyandtelescope"/>

== See also ==
*[[Astronomy:Kepler-90h|Kepler-90h]]
*[[Astronomy:HD 69830 d|HD 69830 d]]
*[[Astronomy:Kepler-47c|Kepler-47c]]

== References ==

{{reflist}}

{{Sky|11|44|41|+|30|57|33}}
{{Stars of Ursa Major}}
{{2011 in space}}

[[Category:Exoplanets detected by radial velocity]]
[[Category:Giant planets in the habitable zone]]

{{Sourceattribution|HIP 57274 d}}