Editing Precovery

{{Short description|Process of finding the image of an object in images or photographic plates predating its discovery}}
[[File:Valetudo CFHT precovery 2003-02-28 annotated.gif|thumb|The Jupiter moon [[Valetudo (moon)|Valetudo]] was first discovered in 2017, but a number of precovery images have been identified since, including this one taken on 28 February 2003 by the [[Canada–France–Hawaii Telescope]], in which Valetudo's position is marked by the two orange bars.]]

In [[astronomy]], '''precovery''' (short for '''pre-discovery recovery''')<ref name="McNaught" /><ref name="AANEAS" /> is the process of finding the image of a [[celestial object]] in images or [[photographic plates]] predating its discovery, typically for the purpose of calculating a more accurate [[orbit]]. This happens most often with [[minor planet]]s, but sometimes a [[comet]], a [[dwarf planet]], a [[natural satellite]], or a [[star]] is found in old archived images; even [[extrasolar planet|exoplanet]] precovery observations have been obtained.<ref name="HST-exoplanet" /> "Precovery" refers to a pre-discovery image; "recovery" refers to imaging of a body which was lost to our view (as behind the Sun), but is now visible again ''(also see [[lost minor planet]] and [[lost comet]])''.

[[Orbit determination]] requires measuring an object's position on multiple occasions.  The longer the interval between observations, the more accurately the orbit can be calculated; however, for a newly discovered object, only a few days' or weeks' worth of measured positions may be available, sufficient only for a preliminary (imprecise) orbit calculation.

When an object is of particular interest (such as [[asteroid]]s with a chance of [[impact event|impacting Earth]]), researchers begin a search for precovery images.  Using the preliminary orbit calculation to predict where the object might appear on old archival images, those images (sometimes decades old) are searched to see if it had in fact already been photographed.  If so, a far longer [[observation arc]] can allow a far more precise orbital calculation.

Until fast computers were widely available, it was impractical to analyze and measure images for possible minor planet discoveries because this required much human labor. Usually, such images were made years or decades earlier for other purposes (studies of [[galaxy|galaxies]], etc.), and it was not worth the time it took to look for precovery images of ordinary asteroids. Today, computers can easily analyze digital astronomical images and compare them to [[star catalog]]s containing up to a [[1000000000 (number)|billion]] or so star positions to see if one of the "stars" is actually a precovery image of the newly discovered object. This technique has been used since the mid-1990s to determine the orbits of many minor planets.

== Examples ==

In an extreme case of precovery, an object was discovered on December 31, 2000, designated {{mpl|2000 YK|66}}, and a near-Earth orbit was calculated. Precovery revealed that it had previously been discovered on February 23, 1950 and given the [[provisional designation]] 1950 DA, and then been lost for half a century. The exceptionally long observation period allowed an unusually precise orbit calculation, and the asteroid was determined to have a small chance of colliding with the Earth. After an asteroid's orbit is calculated with sufficient precision, it can be assigned a number prefix (in this case, [[(29075) 1950 DA]]).

The asteroid [[69230 Hermes]] was found in 2003 and numbered, but was found to be a discovery from 1937 which had been named "Hermes", but subsequently lost; its old name was reinstated. [[Centaur (minor planet)|Centaur]] [[2060 Chiron]] was discovered in 1977, and precovery images from 1895 have been located.<ref name=jpl-chiron />

Another noteworthy case of precovery concerns [[Neptune]]. [[Galileo Galilei|Galileo]] observed Neptune on both December 28, 1612 and January 27, 1613, when it was in a portion of its orbit where it was nearly directly behind Jupiter as seen from Earth. Because Neptune moves very slowly and is very faint relative to the known planets of that time, Galileo mistook it for a [[fixed star]], leaving the planet undiscovered until 1846. He did note that the "star" Neptune did seem to move, noting that between his two observations its apparent distance from another star had changed. However, unlike photographic images, drawings such as those Galileo made are usually not precise enough to be of use in refining an object's orbit. In 1795, [[Jérôme Lalande|Lalande]] also mistook Neptune for a star.<ref name="Price-Handbook" /> In 1690, [[John Flamsteed]] did the same with [[Uranus]], even cataloging it as "[[34 Tauri]]".

One of the most exceptional suggested instances is related to the discovery of [[Ganymede (moon)|Ganymede]]. This again involved Galileo, who is usually stated to have discovered it in 1610. It has been postulated by [[Xi Zezong]] that Ganymede was discovered by the Chinese astronomer [[Gan De]] in 365 B.C., when he catalogued it as a small red star next to Jupiter during naked eye observation.<ref>{{cite web|title=Galilean Moons– Gan De|url=http://www.mediander.com/connects/12505/galilean-moons/#!/topic/1989270/|archive-url=https://web.archive.org/web/20171201041912/http://www.mediander.com/connects/12505/galilean-moons/|archivedate=2017-12-01|accessdate=27 November 2017}}</ref>

=== Dwarf planets ===
Discovery and precovery dates for well-known [[dwarf planet]]s, minor planets and [[List of possible dwarf planets|probable dwarf planets]]:

{| class="wikitable sortable" style="width: 360px; text-align: center;"
!Index|| Object || Discovery<br/>year || Precovery<br/>year
!Years elapsed||[[Absolute magnitude#Apparent magnitude 2|Absolute<BR/>magnitude]]
|- bgcolor=#c0FFc0
|2||[[2 Pallas|Pallas]]||1802||1779<ref>{{cite web|url=http://www.cieletespace.fr/node/7147|title=Charles Messier, premier observateur de l'astéroïde Pallas|website=cieletespace.fr|access-date=7 May 2018|url-status=live|archive-url=https://web.archive.org/web/20160316032302/http://www.cieletespace.fr/node/7147|archive-date=16 March 2016}}</ref>
|23||4.13
|- bgcolor=#c0c0FF
|134340||[[Pluto]]||1930||1909<ref name="Wild-1998" />
|21||-0.7
|- bgcolor=#ffffc0
|19521||[[19521 Chaos|Chaos]]||1998||1991 <ref>{{cite web|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2019521|title=JPL Small-Body Database Browser}}</ref>
|7||5.0
|- bgcolor=#c0FFFF
|20000||[[20000 Varuna|Varuna]]||2000||1954<ref>{{cite web|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2020000|title=JPL Small-Body Database Browser|first=Alan|last=Chamberlin|website=ssd.jpl.nasa.gov|access-date=7 May 2018|url-status=live|archive-url=https://web.archive.org/web/20180507144156/https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2020000|archive-date=7 May 2018}}</ref>
|46||3.76
|- bgcolor=#ffffc0
|38628||[[38628 Huya|Huya]]||2000||1996<ref name=jpl-huya>{{cite web|type=2009-06-13 last obs|title=JPL Small-Body Database Browser: 38628 Huya (2000 EB173)|url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Huya|access-date=2010-02-09|url-status=live|archive-url=https://web.archive.org/web/20180507144156/https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Huya|archive-date=2018-05-07}}</ref>
|4||5.04
|- bgcolor=#ffffc0
|78799||{{mpl-|78799|2002 XW|93}}||2002||1989 <ref>{{cite web|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2078799|title=JPL Small-Body Database Browser}}</ref>
|13||5.5
|- bgcolor=#c0FFFF
|28978||[[28978 Ixion|Ixion]]||2001||1982<ref name=jpl-ixion>{{cite web|type=2009-05-21 last obs|title=JPL Small-Body Database Browser: 28978 Ixion (2001 KX76)|url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Ixion|access-date=2010-02-08|url-status=live|archive-url=https://web.archive.org/web/20151105202412/http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Ixion|archive-date=2015-11-05}}</ref>
|19||3.6
|- bgcolor=#c0FFFF
|55637||{{mpl-|55637|2002 UX|25}}||2002||1991 <ref>{{cite web|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2055637|title=JPL Small-Body Database Browser}}</ref>
|11||3.87
|- bgcolor=#c0c0FF
|50000||[[50000 Quaoar|Quaoar]]||2002||1954<ref name=jpl-quaoar>{{cite web|type=2009-09-12 last obs|title=JPL Small-Body Database Browser: 50000 Quaoar (2002 LM60)|url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=50000|access-date=2010-02-08|url-status=live|archive-url=https://web.archive.org/web/20110611080740/http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=50000|archive-date=2011-06-11}}</ref>
|48||2.82
|- bgcolor=#c0FFFF
|307261||{{mpl-|307261|2002 MS|4}}||2002||1954<ref name=jpl-ms4>{{Cite web |date=2011-12-12 |title=JPL Small-Body Database Browser: (2002 MS4) |url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2002MS4 |access-date=2015-01-28 |url-status=live |archive-url=https://web.archive.org/web/20120415175413/http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2002MS4 |archive-date=2012-04-15 }}</ref>
|48||3.7
|- bgcolor=#c0FFFF
|55565||{{mpl-|55565|2002 AW|197}}||2002||1997 <ref>{{cite web|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2055565|title=JPL Small-Body Database Browser}}</ref>
|5||3.5
|- bgcolor=#ffffc0
|||{{mpl|2002 XV|93}}||2002||1990 <ref>{{cite web|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=3145527|title=JPL Small-Body Database Browser}}</ref>
|12||5.42
|- bgcolor=#c0FFFF
|174567||[[174567 Varda|Varda]]||2003||1980 <ref>{{cite web|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2174567|title=JPL Small-Body Database Browser}}</ref>
|23||3.1
|- bgcolor=#c0FFc0
|84922||{{mpl-|84922|2003 VS|2}}||2003||1991 <ref>{{cite web|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2084922|title=JPL Small-Body Database Browser}}</ref>
|12||4.1
|- bgcolor=#c0FFFF
|208996||{{mpl-|208996|2003 AZ|84}}||2003||1996 <ref>{{cite web|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2208996|title=JPL Small-Body Database Browser}}</ref>
|7||3.54
|- bgcolor=#c0FFc0
|455502||{{mpl-|455502|2003 UZ|413}}||2003||1954 <ref>{{cite web|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2455502|title=JPL Small-Body Database Browser}}</ref>
|49||4.38
|- bgcolor=#c0c0FF
|90377||[[90377 Sedna|Sedna]]||2003||1990<ref name=jpl-sedna>{{cite web|type=2010-01-05 last obs|title=JPL Small-Body Database Browser: 90377 Sedna (2003 VB12)|url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Sedna|access-date=2010-02-08|url-status=live|archive-url=https://archive.today/20160325142222/http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Sedna|archive-date=2016-03-25}}</ref>
|13||1.83
|- bgcolor=#c0FFc0
|444030||{{mpl-|444030|2004 NT|33}}||2004||1982 <ref>{{cite web|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2444030|title=JPL Small-Body Database Browser}}</ref>
|22||4.4
|- bgcolor=#c0FFc0
|230965||{{mpl-|230965|2004 XA|192}}||2004||1989 <ref>{{cite web|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2230965|title=JPL Small-Body Database Browser}}</ref>
|15||4.1
|- bgcolor=#c0FFc0
|90568||{{mpl-|90568|2004 GV|9}}||2004||1954 <ref>{{cite web|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2090568|title=JPL Small-Body Database Browser}}</ref>
|50||4.25
|- bgcolor=#c0c0FF
|90482||[[90482 Orcus|Orcus]]||2004||1951<ref name=jpl-orcus>{{cite web|type=2009-04-28 last obs|title=JPL Small-Body Database Browser: 90482 Orcus (2004 DW)|url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Orcus|access-date=2010-02-08|url-status=live|archive-url=https://web.archive.org/web/20151105202411/http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Orcus|archive-date=2015-11-05}}</ref>
|53||2.2
|- bgcolor=#c0FFc0
|175113||{{mpl-|175113|2004 PF|115}}||2004||1992 <ref>{{cite web|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2175113|title=JPL Small-Body Database Browser}}</ref>
|12||4.54
|- bgcolor=#c0FFc0
|120347||[[120347 Salacia|Salacia]]||2004||1982 <ref>{{cite web|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2120347|title=JPL Small-Body Database Browser}}</ref>
|22||4.36
|- bgcolor=#c0FFc0
|120348||{{mpl-|120348|2004 TY|364}}||2004||1983 <ref>{{cite web|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2120348|title=JPL Small-Body Database Browser}}</ref>
|21||4.52
|- bgcolor=#c0c0FF
|136108||[[Haumea (dwarf planet)|Haumea]]||2004||1955<ref name=jpl-haumea>{{cite web|type=2010-01-26 last obs|title=JPL Small-Body Database Browser: 136108 Haumea (2003 EL61)|url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Haumea|access-date=2010-02-08|url-status=live|archive-url=https://web.archive.org/web/20110609185500/http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Haumea|archive-date=2011-06-09}}</ref>
|49||0.2
|- bgcolor=#c0FFc0
|145451||{{mpl-|145451|2005 RM|43}}||2005||1976 <ref>{{cite web|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2145451|title=JPL Small-Body Database Browser}}</ref>
|29||4.4
|- bgcolor=#c0FFFF
|145452||{{mpl-|145452|2005 RN|43}}||2005||1954 <ref>{{cite web|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2145452|title=JPL Small-Body Database Browser}}</ref>
|51||3.89
|- bgcolor=#c0FFFF
|202421||{{mpl-|202421|2005 UQ|513}}||2005||1990 <ref>{{cite web|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2202421|title=JPL Small-Body Database Browser}}</ref>
|15||3.4
|- bgcolor=#c0c0FF
|136199||[[Eris (dwarf planet)|Eris]]||2005||1954<ref name=jpl-eris>{{cite web|type=2009-11-20 last obs|title=JPL Small-Body Database Browser: 136199 Eris (2003 UB313)|url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Eris|access-date=2010-02-08|url-status=live|archive-url=https://web.archive.org/web/20110512174607/http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Eris|archive-date=2011-05-12}}</ref>
|51||-1.17
|- bgcolor=#c0c0FF
|136472||[[Makemake (dwarf planet)|Makemake]]||2005||1955<ref name=jpl-makemake>{{cite web|type=2010-01-26 last obs|title=JPL Small-Body Database Browser: 136472 Makemake (2005 FY9)|url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Makemake|access-date=2010-02-08|url-status=live|archive-url=https://web.archive.org/web/20110830125730/http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Makemake|archive-date=2011-08-30}}</ref>
|50||-0.3
|- bgcolor=#c0FFc0
|470308||{{mpl-|470308|2007 JH|43}}||2007||1984 <ref>{{cite web|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2470308|title=JPL Small-Body Database Browser}}</ref>
|23||4.49
|- bgcolor=#c0FFFF
|229762||[[229762 Gǃkúnǁʼhòmdímà|Gǃkúnǁʼhòmdímà]]||2007||1982 <ref>{{cite web|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2229762|title=JPL Small-Body Database Browser}}</ref>
|25||3.69
|- bgcolor=#c0c0FF
|225088||[[225088 Gonggong|Gonggong]]||2007||1985<ref name=jpl-or10>{{cite web|type=2009-10-19 last obs|title=JPL Small-Body Database Browser: 225088 (2007 OR10)|url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2007OR10|access-date=2010-02-08|url-status=live|archive-url=https://web.archive.org/web/20111115202044/http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2007OR10|archive-date=2011-11-15}}</ref>
|22||1.8
|- bgcolor=#c0FFc0
|523671||{{mpl-|523671|2013 FZ|27}}||2013||2001<ref name=jpl-fz27>{{cite web|type=2014-03-26 last obs|title=JPL Small-Body Database Browser: 2013 FZ27)|url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2013FZ27|access-date=2015-04-13}}</ref>
|12||4.1
|- bgcolor=#ffffc0
|472271||{{mpl-|472271|2014 UM|33}}||2014||2003 <ref>{{cite web|url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2472271|title=JPL Small-Body Database Browser}}</ref>
|11||5.2
|- bgcolor=#c0FFFF
|523794||{{mpl-|523794|2015 RR|245}}||2015||2004<ref name=jpl-rr245>{{cite web|type=2016-06-08 last obs|title=JPL Small-Body Database Browser: 2015 RR245)|url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2015RR245|access-date=2016-12-26|url-status=live|archive-url=https://web.archive.org/web/20161227055749/http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2015RR245|archive-date=2016-12-27}}</ref>
|11||3.6
|- bgcolor=#c0FFFF
|||{{mpl|2018 VG|18}}||2018||2003 <ref>{{cite web|url=https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=2018%20VG18|title=JPL Small-Body Database Browser}}</ref>
|15|| 3.5
|}

=== Oort cloud comets ===
Oort cloud comets can take 10+ years going from [[Neptune]]'s orbit at {{Convert|30.1|AU|e9km|abbr=unit|lk=on}} to [[perihelion]] (closest approach to the Sun). As modern [[Astronomical survey|survey]] archives reach fainter magnitudes and are more comprehensive, significant precovery images have become easier to locate.

{| class="wikitable sortable" style="text-align:center;"
|+Oort Cloud Comets
!Comet
!data-sort-type="number"|Discovery<br />date
!data-sort-type="number"|Precovery<br />date
!data-sort-type="number"|Discovery<br />distance<br />from Sun (AU)
!data-sort-type="number"|Precovery<br />distance<br />from Sun (AU)
!Ref
|-
|'''[[C/2010 U3 (Boattini)]]''' || 2010-10-31 || 2005-11-05 || 18.4 || 25.8 || {{JPL|2010+U3}}
|-
|'''[[C/2012 S1 (ISON)]]''' || 2012-09-21 || 2011-09-30 || 6.3 || 9.4 || {{JPL|2012+S1}}
|-
|'''[[C/2013 A1 (Siding Spring)]]''' || 2013-01-03 || 2012-10-04 || 7.2 || 7.9 || {{JPL|2013+A1}}
|-
|'''[[C/2017 K2|C/2017 K2 (PANSTARRS)]]''' || 2017-05-21 || 2013-05-12 || 16.1 || 23.7 || {{JPL|2017+K2}}
|}

== See also ==

* [[Discovery image]]
* [[DANEOPS]]

== References ==
{{Reflist|refs=

<ref name="Wild-1998">{{cite journal
  |author1=Wild, W. J. |author2=Buchwald, G. |author3=Dimario, M. J. |author4=Standish, E. M.
  |date       = December 1998
  |title      = Serendipitous Discovery of the Oldest Known Photographic Plates with Images of Pluto
  |journal    = American Astronomical Society
  |volume     = 30
  |page       = 1449
  |bibcode    = 1998DPS....30.5514W
  }}</ref>

<ref name="McNaught">{{cite conference
  |author=McNaught, R. H.
  |author2=Steel, D. I.
  |author3=Russell, K. S.
  |author4=Williams, G. V.
  |date=March 7–11, 1994
  |title=Near-Earth Asteroids on Archival Schmidt Plates
  |book-title=Proceedings, The future utilisation of Schmidt telescopes
  |conference=IAU Colloquium 148
  |publisher=[[Astronomical Society of the Pacific]]
  |volume=84
  |location=Bandung, Indonesia
  |editor=Jessica Chapman
  |editor2=Russell Cannon
  |editor3=Sandra Harrison
  |editor4=Bambang Hidayat
  |editor4-link=Bambang Hidayat
  |pages=170
  |bibcode=1995ASPC...84..170M
  }}</ref>

<ref name="AANEAS">{{cite web|url=http://users.tpg.com.au/users/tps-seti/spacegd4.html|title=AANEAS: A Valedictory Report|archive-url=https://web.archive.org/web/20120728155155/http://users.tpg.com.au/users/tps-seti/spacegd4.html|archive-date=2012-07-28|author=D.I. Steel, R.H. McNaught, G.J. Garradd, D.J. Asher and K.S. Russell|date=25 March 1997}}</ref>

<ref name="HST-exoplanet">{{cite web
 |last        = Villard
 |first       = Ray
 |author2     = Lafreniere, David
 |title       = Hubble Finds Hidden Exoplanet in Archival Data
 |work        = HubbleSite NewsCenter
 |publisher   = [[NASA]]
 |date        = April 1, 2009
 |url         = https://hubblesite.org/contents/news-releases/2009/news-2009-15.html?Year=2009&Topic=103-exoplanets
 |access-date  = 2024-06-25
 |url-status     = live
 |archive-url  = https://web.archive.org/web/20090405172053/http://hubblesite.org/newscenter/archive/releases/2009/15/full/
 |archive-date = April 5, 2009
}}</ref>

<ref name=jpl-chiron>{{cite web
 |type        = 2009-09-17 last obs
 |title       = JPL Small-Body Database Browser: 2060 Chiron (1977 UB)
 |url         = http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Chiron
 |access-date  = 2010-02-08
 |url-status     = live
 |archive-url  = https://web.archive.org/web/20110609185528/http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Chiron
 |archive-date = 2011-06-09
}}</ref>

<ref name="Price-Handbook">{{cite book
  |title      = The planet observer's handbook
  |author     = Fred William Price
  |publisher  = [[Cambridge University Press]]
  |url        = https://archive.org/details/planetobserversh00pric
  |url-access = registration
  |page       = [https://archive.org/details/planetobserversh00pric/page/352 352]
  |date       = 2000
  |access-date = 2009-09-11|isbn     = 9780521789813
  }}</ref>

}} <!-- end of reflist -->

== External links ==
{{wiktionary|precovery}}
* [http://skyview.gsfc.nasa.gov/skymorph/skymorph.html SkyMorph GSFC]

[[Category:Planetary science]]
[[Category:Photography]]