View source for Elara (moon)

{{Short description|Outer moon of Jupiter}}
{{Use dmy dates|date=November 2020}}
{{Infobox planet
| name = Elara
| image = File:Elara - New Horizons.png
| caption =  Low-resolution image of Elara from the ''[[New Horizons]]'' probe, March 2007
| pronounced = {{IPAc-en|ˈ|ɛ|l|ə|r|ə}}<ref>[[James Knowles (lexicographer)|James Knowles]] (1851) ''A Critical Pronouncing Dictionary of the English Language''</ref>
| adjectives = Elarian {{IPAc-en|ɛ|ˈ|l|ɛər|i|ə|n}}
| named_after = [[Elara (mythology)|Ελάρα]] ''Elăra''<ref>[http://dge.cchs.csic.es/xdge/%E1%BC%98%CE%BB%CE%AC%CF%81%CE%B1 DGE en línea]</ref>
| mpc_name = Jupiter VII
| alt_names = 
| discovery_ref = <ref name="Harvard1905"/><ref name="Perrine1905"/>
| discoverer = [[Charles Dillon Perrine|Charles D. Perrine]]
| discovery_site = [[Lick Observatory]]
| discovered = 5 January 1905
| earliest_precovery_date = 
| satellite_of = [[Jupiter]]
| group = [[Himalia group]]
| orbit_ref = <ref name="MPC115889"/>
| epoch = 27 April 2019 ([[Julian day|JD]] 2458600.5)
| observation_arc = 113.70 [[Julian year (astronomy)|yr]] (41,528 days)
| semimajor = {{cvt|0.0782306|AU|km|lk=in}}
| eccentricity = 0.1961487
| period = +258.65 d
| mean_anomaly = 10.93078[[Degree (angle)|°]]
| mean_motion = {{Deg2DMS|1.39185275|sup=ms}} / day
| inclination = 30.51712° (to [[ecliptic]])
| asc_node = 90.86474°
| arg_peri = 191.19922°
| mean_diameter = {{val|79.9|1.7|u=km}}<ref name="Grav2015"/>
| mass = 
| density = <!-- assumed density of 2.6 g/cm3 from JPL -->
| surface_grav = 
| escape_velocity = 
| rotation = 
| albedo = {{val|0.046|0.007}}<ref name="Grav2015"/>
| magnitude = 16.6<ref name="SheppardMoons"/>
| abs_magnitude = 9.6<ref name="MPC115889"/>
}}

'''Elara''' {{IPAc-en|ˈ|ɛ|l|ə|r|ə}} is a [[Retrograde and prograde motion|prograde]] [[Irregular moon|irregular]] [[natural satellite|satellite]] of [[Jupiter]]. It was discovered by [[Charles Dillon Perrine]] at [[Lick Observatory]] in 1905 in photographs taken with the 36" Crossley reflecting telescope which he had recently rebuilt.<ref name="Harvard1905"/><ref name="Perrine 1905"/> It is the eighth-largest moon of Jupiter and is named after [[Elara (mythology)|Elara]], one of [[Zeus]]'s lovers and the mother of the giant [[Tityos]].<ref name="IAUC 2846">{{cite web|last=Marsden |first=Brian G. |title=Satellites of Jupiter |publisher=[[International Astronomical Union]] |date=7 October 1975 |url=http://www.cbat.eps.harvard.edu/iauc/02800/02846.html |url-status=dead |archive-url=https://web.archive.org/web/20140222215122/http://www.cbat.eps.harvard.edu/iauc/02800/02846.html |archive-date=22 February 2014}}</ref>

Elara did not receive its present name until 1975; before then, it was simply known as '''{{nowrap|Jupiter VII}}'''. It was sometimes called "[[Hera]]"<ref name="Gaposchkin">{{cite book| last=Payne-Gaposchkin|first=Cecilia|author2=Katherine Haramundanis|title=Introduction to Astronomy|year=1970|publisher=[[Prentice-Hall]]|location=Englewood Cliffs, N.J.|isbn=0-13-478107-4}}</ref> between 1955 and 1975. It has a [[mean radius]] of just {{convert|43|km}}, thus it is 2% of the size of [[Europa (moon)|Europa]]. However, it is half the size of [[Himalia (moon)|Himalia]], so it is the second-biggest moon in the [[Himalia group]]. It might be a captured type C or D asteroid, for it reflects very little light.

Elara belongs to the Himalia group, moons orbiting between 11 and 13&nbsp;[[Orders of magnitude (length)#1 gigametre|gigametres]] from Jupiter at an inclination of about 27.5°.<ref name="Jacobson 2000">{{cite journal| last=Jacobson| first=R. A.|title=The orbits of outer Jovian satellites|journal=Astronomical Journal| year=2000| volume=120| issue=5| pages=2679–2686|doi=10.1086/316817| bibcode=2000AJ....120.2679J| s2cid=120372170|url=https://trs.jpl.nasa.gov/bitstream/2014/15175/1/00-1187.pdf}}</ref> Its orbital elements are as of January 2000. They are continuously changing due to [[Sun|solar]] and planetary perturbations.

==Discovery==
Elara was discovered by [[Charles Dillon Perrine]] of the Lick Observatory on January 6, 1905, the day after the discovery of [[Himalia (moon)|Himalia]], also by Perrine, was announced. However, poor weather conditions delayed the confirmation of the discovery till the 21st of February.<ref>{{cite web|url=https://www.newspapers.com/clip/110687001/elara-discovery/|title=Jupiter's Newly Discovered Moons and Solar Cyclones|last1=Proctor|first1=Mary|date=March 5, 1905|website=The New York Times|accessdate=October 4, 2022}}</ref>

== Exploration ==
=== New Horizons encounter ===
In February and March 2007, the ''[[New Horizons]]'' spacecraft to [[Pluto]] captured Elara in several [[LORRI (New Horizons)|LORRI]] images from a distance of {{convert|5|e6mi|e6km|abbr=unit|order=flip|0}}.<ref>{{cite book |last1=Hamilton |first1=Thomas Wm. |title=Moons of the solar system |date=2013 |publisher=Strategic Book Publishing |isbn=978-1625161758 |page=21 |url=https://books.google.com/books?id=wg4ELSuruqQC&pg=PA21}}</ref>

{{clear|left}}

==See also==
* [[Jupiter's moons in fiction]]

==References==
{{reflist|refs=

<ref name="Harvard1905">{{cite journal| last=Perrine|first=C. D.|title=Satellites of Jupiter|journal=Harvard College Observatory Bulletin |volume=178|date=27 February 1905 |url=http://adsabs.harvard.edu//full/seri/BHarO/0178//0000001.000.html}}</ref><ref name="Perrine 1905">{{cite journal| last=Perrine| first=C. D.|title=The Seventh Satellite of Jupiter|journal=Publications of the Astronomical Society of the Pacific| year=1905| volume=17| issue=101|pages= 62–63|bibcode=  1905PASP...17...56.| doi=10.1086/121624| jstor=40691209| doi-access=free}}</ref>

<ref name="Perrine1905">{{cite journal| last=Perrine| first=C. D.|title=The Seventh Satellite of Jupiter|journal=Publications of the Astronomical Society of the Pacific| year=1905| volume=17| issue=101|pages= 62–63|bibcode=  1905PASP...17...56.| doi=10.1086/121624| jstor=40691209| doi-access=free}}</ref>

<ref name="MPC115889">{{cite web
  |title      = M.P.C. 115889
  |url        = https://minorplanetcenter.net/iau/ECS/MPCArchive/2019/MPC_20190827.pdf
  |work       = Minor Planet Circular
  |publisher  = Minor Planet Center
  |date       = 27 August 2019}}</ref>

<ref name="SheppardMoons">{{cite web
  |title      = Scott S. Sheppard - Jupiter Moons
  |url        = https://sites.google.com/carnegiescience.edu/sheppard/moons/jupitermoons
  |last       = Sheppard |first = Scott
  |work       = Department of Terrestrial Magnetism 
  |publisher  = Carnegie Institution for Science
  |access-date = 26 November 2020}}</ref>

<ref name="Grav2015">{{cite journal
  |display-authors = etal
  |first1     = T. |last1 = Grav
  |first2     = J. M. |last2 = Bauer
  |first3     = A. K. |last3 = Mainzer
  |first4     = J. R. |last4 = Masiero
  |first5     = C. R. |last5 = Nugent
  |first6     = R. M. |last6 = Cutri
  |date       = August 2015
  |title      = NEOWISE: Observations of the Irregular Satellites of Jupiter and Saturn
  |journal    = The Astrophysical Journal
  |volume     = 809
  |issue      = 1
  |id         = 3
  |pages      = 9
  |doi        = 10.1088/0004-637X/809/1/3
  |arxiv = 1505.07820 |bibcode    = 2015ApJ...809....3G|s2cid = 5834661 }}</ref>

}}

==External links==
* [https://web.archive.org/web/20171114145110/https://www.imcce.fr/page.php?nav=fr%2Fephemerides%2Fastronomie%2FPromenade%2Fpages3%2F35.html Elara on 1998-08-15 03:21 UTC](Crédit: OHP/[[IMCCE]]/[[CNRS]])
* [http://skyview.gsfc.nasa.gov/current/cgi/runquery.pl?Interface=quick&Position=23+47+09+-02+40+46&SURVEY=Digitized+Sky+Survey SkyView 23 47 09 -02 40 46]
* [http://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&body_group=mb&sstr=507 HORIZONS Web-Interface], JPL
* [https://web.archive.org/web/20160406124234/http://solarsystem.nasa.gov/planets/elara Elara: Overview] by [http://solarsystem.nasa.gov NASA's Solar System Exploration]
* [https://web.archive.org/web/20060901072706/http://www.ifa.hawaii.edu/~jewitt/irregulars.html David Jewitt pages]
* [http://remanzacco.blogspot.co.uk/2012/11/two-irregular-satellites-of-jupiter.html"Two Irregular Satellites of Jupiter"] (Himalia & Elara: Remanzacco Observatory: November 23, 2012)

{{Moons of Jupiter}}

{{DEFAULTSORT:Elara (Moon)}}
[[Category:Himalia group]]
[[Category:Moons of Jupiter]]
[[Category:Irregular satellites]]
[[Category:Astronomical objects discovered in 1905|19050105]]
[[Category:Discoveries by Charles D. Perrine]]
[[Category:Moons with a prograde orbit]]