View source for 81P/Wild

{{Short description|Periodic comet with six-year orbit}}
{{Use mdy dates|date=January 2012}}
{{Infobox comet
| name            = 81P/Wild
| image           = Wild2 3.jpg
| caption         = The [[Comet nucleus|nucleus]] of Comet Wild 2 as seen by the ''[[Stardust (spacecraft)|Stardust]]'' mission in January 2004
| discovery_ref   = {{r|IAUC_3166}}
| discoverer      = [[Paul Wild (Swiss astronomer)|Paul Wild]]
| discovery_site  = [[Zimmerwald Observatory|Zimmerwald]], Switzerland
| discovery_date  = 6 January 1978
| mpc_name        = P/1978 A2; P/1983 S1
| designations    = 1978 XI; 1984 XIV;<br>1990 XXVIII
| orbit_ref       = {{r|jpldata|mpc}}
| epoch           = 17 October 2024 ([[Julian day|JD]] 2460600.5)
| observation_arc = 46.67 years
| obs             = 7,963
| perihelion      = 1.597 AU
| aphelion        = 5.307 AU
| semimajor       = 3.452 AU
| eccentricity    = 0.53739
| period          = 6.414 years
| inclination     = 3.237°
| asc_node        = 136.09°
| arg_peri        = 41.568°
| mean            = 103.17°
| tjup            = 2.879
| Earth_moid      = 0.601 AU
| Jupiter_moid    = 0.012 AU
| physical_ref    = {{r|jpldata|Britt_2006|tps1}}
| dimensions      = {{cvt|5.5|x|4.0|x|3.3|km|mi}}
| density         = 
{{cvt|0.6|g/cm3|lb/cuft}}
| mass            = 2.3 x 10<sup>13</sup> kg (5.1 x 10<sup>13</sup> lb){{efn|Using the [[Volume#Formulas|volume of an ellipsoid]] of 5.5×4.0×3.3&nbsp;km * a [[rubble pile]] density of 0.6 g/cm<sup>3</sup> yields a mass (m{{=}}d*v) of 2.28{{e|13}} kg}}
| M1              = 9.8
| M2              = 12.9
| magnitude       = 
| last_p          = 15 December 2022
| next_p          = 14 May 2029{{r|Horizons2029}}
}}

Comet '''81P/Wild''', also known as '''Wild 2''' (pronounced "vilt two") ({{IPAc-en|ˈ|v|ɪ|l|t}} {{respell|VILT|'}}), is a [[comet]] with a period of 6.4 years named after Swiss astronomer [[Paul Wild (Swiss astronomer)|Paul Wild]], who discovered it on January 6, 1978, using a 40-cm [[Schmidt telescope]] at [[Zimmerwald Observatory|Zimmerwald]], Switzerland.{{r|IAUC_3166}}

For most of its 4.5 billion-year lifetime, Wild 2 probably had a more distant and [[circular orbit]]. In September 1974, it passed within {{convert|1.0|e6km|e6mi|abbr=unit}} of the planet [[Jupiter]], the strong gravitational pull of which [[Perturbation (astronomy)|perturbed]] the comet's [[orbit]] and brought it into the [[inner Solar System]].{{r|kronk}} Its [[orbital period]] changed from 43 years to about 6 years,{{r|kronk}} and its [[perihelion]] is now about {{convert|1.59|AU|e6km|abbr=unit}}.{{r|mpc}}

== Orbit ==
Prior to its encounter with Jupiter in 1974, the comet had an orbital period of around 43 years with an aphelion at around 25 AU and a perihelion of just under 5 AU. The encounter reduced the aphelion and perihelion to its present value of around 5 and 1.5 AU, respectively.{{r|Ogliore_2023}}

== Exploration ==
[[File:Comet 81P Wild 2010-01-17.jpg|thumb|left|Wild 2 from Earth]]
[[File:Animation of Stardust trajectory.gif|left|thumb|Animation of ''Stardust'' {{'s}} trajectory from 7 February 1999 to 7 April 2011<br />{{legend2|magenta| Stardust }}{{·}}{{legend2|lime|81P/Wild}}{{·}}{{legend2|Royalblue|[[Earth]]}}{{·}}{{legend2|Cyan|[[5535 Annefrank]] }}{{·}}{{legend2|Gold|[[Tempel 1]] }}]]

NASA's [[Stardust Mission]] launched a [[spacecraft]], named ''[[Stardust (spacecraft)|Stardust]]'', on February 7, 1999.  It flew by Wild 2 on January 2, 2004, and collected particle samples from the comet's [[Coma (cometary)|coma]], which were returned to Earth along with [[interstellar dust]] it collected during the journey. Seventy-two close-up shots were taken of Wild 2 by ''Stardust''. They revealed a surface riddled with flat-bottomed depressions, with sheer walls and other features that range from very small to up to {{cvt|2|km|mi}} across. These features are believed to be caused by impact craters or gas vents. During ''Stardust''{{'}}s flyby, at least 10 gas vents were active. The comet itself has a diameter of {{cvt|5|km|mi}}.

''Stardust''{{'}}s "sample return canister" was reported to be in excellent condition when it landed in Utah, on January 15, 2006. A NASA team analyzed the particle capture cells and removed individual grains of comet and interstellar dust, then sent them to about 150 scientists around the globe.{{r|NASA-20060118}} NASA is collaborating with [[The Planetary Society]] who will run a project called "[[Stardust@Home]]", using volunteers to help locate particles on the Stardust Interstellar Dust Collector (SIDC).

As of 2006,{{r|McKeegan_2006}} the composition of the dust has contained a wide range of organic compounds, including two that contain biologically usable nitrogen. Indigenous aliphatic hydrocarbons were found with longer chain lengths than those observed in the diffuse interstellar medium. No hydrous silicates or carbonate minerals were detected, which suggests a lack of aqueous processing of Wild 2 dust. Very few pure carbon ([[CHON]]) particles were found in the samples returned. A substantial amount of crystalline silicates such as [[olivine]], [[anorthite]] and [[diopside]] were found,{{r|Stricherz_2006}} materials only formed at high temperature. This is consistent with previous observations of crystalline silicates both in cometary tails and in circumstellar disks at large distances from the star. Possible explanations for this high temperature material at large distances from Sun were summarised before the ''Stardust'' sample return mission by van Boekel et al.:{{r|van_Boekel_2004}}

:"Both in the Solar System and in circumstellar disks crystalline silicates are found at large distances from the star. The origin of these silicates is a matter of debate. Although in the hot inner-disk regions crystalline silicates can be produced by means of gas-phase condensation or thermal annealing, the typical grain temperatures in the outer-disk (2–20 au) regions are far below the glass temperature of silicates of approx 1,000 K. The crystals in these regions may have been transported outward through the disk or in an outward-flowing wind.{{r|Liffman_1995}} An alternative source of crystalline silicates in the outer disk regions is in situ annealing, for example by shocks or lightning. A third way to produce crystalline silicates is the collisional destruction of large parent bodies in which secondary processing has taken place. We can use the mineralogy of the dust to derive information about the nature of the primary and/or secondary processes the small-grain population has undergone."

Results from a study reported in the September 19, 2008 issue of the journal ''[[Science (journal)|Science]]'' has revealed an oxygen isotope signature in the dust that suggests an unexpected mingling of rocky material between the center and edges of the Solar System.{{r|Ishii_2008}} Despite the comet's birth in the icy reaches of outer space beyond Pluto, tiny crystals collected from its halo appear to have been forged in the hotter interior, much closer to the Sun.{{r|newswise1}}

In April 2011, scientists from the [[University of Arizona]] discovered evidence of the presence of liquid water. They found iron and [[copper sulfide]] minerals that must have formed in the presence of water. The discovery is in conflict with the existing paradigm that comets never get warm enough to melt their icy bulk. Either [[Impact event|collisions]] or [[Radioactive decay|radiogenic heating]] might have provided the necessary energy source.{{r|LeBlanc_2011}}

On August 14, 2014, scientists announced the collection of possible [[interstellar dust]] particles from the [[Stardust (spacecraft)|''Stardust'' spacecraft]] since returning to Earth in 2006.{{r|NASA-20140814|AP-20140814|Hand_2014|Westphal_2014}}

== Gallery ==
{| class=wikitable style="text-align:center; font-size:11px; float:right; margin:2px"
|- bgcolor= style="font-size: smaller;"
| colspan="8" style="text-align:center;"|'''The Inward Migration of 81P'''
|-
! Year<br />([[Epoch (astronomy)|epoch]]) !! [[Semi-major axis|Semi-major<br />axis]] (AU) !! [[Apsis|Perihelion]]<br />(AU) !! Aphelion<br />(AU)
|-
| 1965 || 13 || 4.95{{r|kronk}} || 21{{efn|In 1951, comet 81P/Wild was at aphelion {{convert|21|AU|e9km|abbr=unit}} from the Sun.{{r|Horizons}}}}
|-
| 1978{{r|mpc}} || 3.36 || 1.49 || 5.24
|}

<gallery class="center">
File:Wild2 3.jpg|Photograph taken by ''Stardust'' spacecraft
File:Comet wild 2 jet plumes.jpg|Details of the plume jets
File:Comet Wild2 Anaglyph.jpg|Red/green stereo anaglyph
File:Comet Wild2 .jpg|''Stardust'' approach image
File:Comet wild 2.jpg
</gallery>

== See also ==
Wild 2 has a similar name to other objects:
* [[116P/Wild]]
* [[1941 Wild]] ({{mp|1931 TN|1}})
* [[63P/Wild]]
* [[86P/Wild]]

== References ==
=== Notes ===
{{notelist}}

=== Citations ===
{{reflist|refs=

<ref name="AP-20140814">{{cite news
| author1= M. Dunn
| title= Specks returned from space may be alien visitors
| url= http://apnews.excite.com/article/20140814/us-sci--alien_stardust-9d21e5267a.html
| work= [[AP News]]
| date= 14 August 2014
| access-date= 15 August 2014
| archive-date= 19 August 2014
| archive-url= https://web.archive.org/web/20140819102935/http://apnews.excite.com/article/20140814/us-sci--alien_stardust-9d21e5267a.html
| url-status= dead }}
</ref>

<ref name="Britt_2006">{{cite web
| author1= D. T. Britt
| author2= S. G. J. Consol-magno
| author3= W. J. Merline
| title= Small Body Density and Porosity: New Data, New Insights
| url= http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2214.pdf
| publisher= Lunar and Planetary Science XXXVII
| date= 2006
| access-date= 16 December 2008
| archive-date= 17 December 2008
| archive-url= https://web.archive.org/web/20081217064607/http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2214.pdf
| url-status= dead }}
</ref>

<ref name="Hand_2014">{{cite journal
| author1= E. Hand
| title= Seven grains of interstellar dust reveal their secrets
| url= https://www.science.org/content/article/seven-grains-interstellar-dust-reveal-their-secrets
| journal= Science
| date= 14 August 2014
| access-date= 15 August 2014 }}
</ref>

<ref name="Horizons2029">{{cite web
| title= Horizons Batch for 81P/Wild 2 (90000856) on 2029-May-14
| publisher= [[JPL Horizons On-Line Ephemeris System|JPL Horizons]]
| type= Perihelion occurs when rdot flips from negative to positive
| url= https://ssd.jpl.nasa.gov/api/horizons.api?format=text&COMMAND=%27DES%3D81P%3BCAP%27&START_TIME=%272029-May-14%27&STOP_TIME=%272029-May-16%27&STEP_SIZE=%273%20hours%27&QUANTITIES=%2719%27
| access-date= 6 July 2023}} (JPL#K222/19 Soln.date: 2023-Jul-06)</ref>

<ref name="Horizons">{{cite web
| author= [[JPL Horizons On-Line Ephemeris System|Horizons]] output
| url= http://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&body_group=sb&sstr=81P%20[1978
| title= Comet 81P/Wild 2 [1978] (SAO/1978)
| access-date= 26 February 2017 }} (Observer Location:@Sun)
</ref>

<ref name="IAUC_3166">{{cite journal
| author1= P. Wild
| editor1= B. G. Marsden
| title= Comet Wild (1978b)
| url= http://www.cbat.eps.harvard.edu/iauc/03100/03166.html
| journal= IAU Circular
| volume= 3166
| pages= 1
| year= 1978
| bibcode= 1978IAUC.3166....1W }}
</ref>

<ref name="Ishii_2008">{{Cite journal
| author1= H. A. Ishii
| author2= J. P. Bradley
| author3= Z. R. Dai
| author4= M. Chi
| author5= A. T. Kearsley
| author6= M. J. Burchell
| author7= N. D. Browning
| author8= F. Molster
| display-authors= 4
| title= Comparison of Comet 81P/Wild 2 Dust with Interplanetary Dust from Comets
| url= https://www.science.org/doi/10.1126/science.1150683
| journal= Science 
| year= 2008
| volume= 319
| issue= 5862
| pages= 447–450
| bibcode= 2008Sci...319..447I
| issn= 0036-8075
| pmid= 18218892
| doi= 10.1126/science.1150683 | url-access= subscription
}}
</ref>

<ref name="jpldata">{{cite web
| title= 81P/Wild 2 – JPL Small-Body Database Lookup
| url= http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=81P
| website= ssd.jpl.nasa.gov
| publisher= [[Jet Propulsion Laboratory]]
| access-date= 26 February 2017 }}
</ref>

<ref name="kronk">{{cite web
| author1= G. W. Kronk
| title= 81P/Wild 2
| url= https://cometography.com/pcomets/081p.html
| website= Cometography.com
| access-date= 23 October 2008 }}
</ref>

<ref name="LeBlanc_2011">{{cite web
| author1= C. LeBlanc
| title= Evidence for liquid water on the surface of Comet Wild-2|url=http://earthsky.org/space/evidence-for-liquid-water-on-the-surface-of-comet-wild-2
| date= 7 April 2011
| access-date= 8 April 2011
| archive-date= 12 May 2011
| archive-url= https://web.archive.org/web/20110512154305/http://earthsky.org/space/evidence-for-liquid-water-on-the-surface-of-comet-wild-2
| url-status= live }}
</ref>

<ref name="Liffman_1995">{{cite journal
| author1= K. Liffman
| author2= M. Brown
| title= The motion and size sorting of particles ejected from a protostellar accretion disk
| journal= Icarus
| year= 1995
| volume= 116
| issue= 2
| pages= 275–290
| bibcode= 1995Icar..116..275L
| doi= 10.1006/icar.1995.1126 }}
</ref>

<ref name="McKeegan_2006">{{cite journal
| author1= K. D. McKeegan
| author2= J. Aléon
| author3= J. Bradley
| author4= D. Brownlee
| author5= H. Busemann
| display-authors= etal
| title= Light element isotopic compositions of cometary matter returned by the STARDUST mission
| journal= Science
| year= 2006
| volume= 314
| issue= 5806
| pages= 1724–1728
| bibcode= 2006Sci...314.1724M
| doi= 10.1126/science.1135992 }}
</ref>

<ref name="mpc">{{cite web
| title= 81P/Wild Orbit
| url= http://www.minorplanetcenter.net/db_search/show_object?object_id=81P
| publisher= [[Minor Planet Center]]
| access-date= 26 February 2017 }}
</ref>

<ref name="NASA-20060118">{{cite web
| author1= J. Williams
| title= Scientists Confirm Comet Samples, Briefing Set Thursday
| url= http://www.nasa.gov/mission_pages/stardust/news/J06-005.html
| publisher= [[NASA]]
| date= 18 January 2006
| access-date= 5 March 2008
| archive-date= 9 March 2008
| archive-url= https://web.archive.org/web/20080309065927/http://www.nasa.gov/mission_pages/stardust/news/J06-005.html
| url-status= live }}
</ref>

<ref name="NASA-20140814">{{cite web
| author1= D. C. Agle
| author2= D. C. Brown
| author3= J. Williams
| title= Stardust Discovers Potential Interstellar Space Particles
| url= http://www.jpl.nasa.gov/news/news.php?release=2014-278
| publisher= [[NASA]]
| date= 14 August 2014
| access-date= 15 August 2014 }}
</ref>

<ref name="newswise1">{{cite web
| author1= University of Wisconsin-Madison
| title= Comet Dust Reveals Unexpected Mixing of Solar System
| url= http://newswise.com/articles/view/544352/
| publisher= Newswise
| date= 15 September 2008
| access-date= 18 September 2008 }}</ref>

<ref name="Ogliore_2023">{{cite journal 
| author1= R. C. Ogliore
| title= Comet 81P/Wild 2: A record of the Solar System's wild youth
| journal= Geochemistry
| year= 2023
| volume= 83
| issue= 4
| pages= 126046
| arxiv= 2311.18119
| issn= 0009-2819
| doi= 10.1016/j.chemer.2023.126046 }}</ref>

<ref name="Stricherz_2006">{{cite web
| author1= V. Stricherz
| title= Comet from coldest spot in solar system has material from hottest places
| url= http://www.uwnews.org/article.asp?articleID=23093
| publisher= [[University of Washington]]
| date= 13 March 2006
| access-date= 5 March 2008
| archive-date= 16 October 2007
| archive-url= https://web.archive.org/web/20071016214113/http://uwnews.org/article.asp?articleID=23093
| url-status= dead }}
</ref>

<ref name="tps1">{{cite web
| title= Comet 81P/Wild 2  
| url= http://www.planetary.org/explore/topics/asteroids_and_comets/wild2.html
| publisher= [[The Planetary Society]]
| access-date= 16 December 2008
| archive-date= 6 January 2009
| archive-url= https://web.archive.org/web/20090106004009/http://planetary.org./explore/topics/asteroids_and_comets/wild2.html
| url-status= dead }}
</ref>

<ref name="van_Boekel_2004">{{cite journal
| author1= R. van Boekel
| author2= M. Min
| author3= C. Leinert
| author4= L. B. F. M. Waters
| author5= A. Richichi
| display-authors= etal
| title= The building blocks of planets within the 'terrestrial' region of protoplanetary disks
| journal= Nature
| year= 2004
| volume= 432
| issue= 7016
| pages= 479–482
| bibcode= 2004Natur.432..479V
| s2cid= 4362887
| pmid= 15565147
| doi= 10.1038/nature03088 }}
</ref>

<ref name="Westphal_2014">{{cite journal
| author1= A. J. Westphal
| author2= R. M. Stroud
| author3= H. A. Bechtel
| author4= F. E. Brenker
| author5= A. L. Butterworth
| display-authors= etal
| title= Evidence for interstellar origin of seven dust particles collected by the ''Stardust'' spacecraft
| url= https://figshare.com/articles/journal_contribution/10129433
| journal= Science
| year= 2014
| volume= 345
| issue= 6198
| pages= 786–791
| bibcode= 2014Sci...345..786W
| s2cid= 206556225 
| pmid= 25124433
| doi= 10.1126/science.1252496
| hdl= 2381/32470
| hdl-access= free }}
</ref>

}}

== External links ==
* {{JPL Small Body|id=1000107}}
* [https://solarsystem.nasa.gov/stardust/home/index.html NASA/JPL homepage for Stardust project]
* [http://stardustathome.ssl.berkeley.edu Stardust@Home Volunteer Particle Analysis Project]
* [http://www.minorplanetcenter.net/db_search/show_object?object_id=81p 81P/Wild orbit and observations at IAU Minor Planet Center]

{{PeriodicComets Navigator|80P/Peters–Hartley|82P/Gehrels}}
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{{DEFAULTSORT:Wild, 081P}}
[[Category:Periodic comets]]
[[Category:Numbered comets|0081]]
[[Category:Jupiter-family comets|081P]]
[[Category:Discoveries by Paul Wild (Swiss astronomer)| ]]
[[Category:Comets visited by spacecraft]]
[[Category:Comets in 2016|081P]]
[[Category:Astronomical objects discovered in 1978|19780106]]