View source for Astronomy:(225088) 2007 OR10

{{DISPLAYTITLE:{{mp|(225088) 2007 OR|10}}}}
{{Infobox planet
 | minorplanet     = yes
 | background      = #C2E0FF
 | name            = {{mp|(225088) 2007 OR|10}}
 | image           = 2007 OR10 and its moon.png
 | image_size      = 250
 | caption         = {{mp|2007 OR|10}} and its moon (red circle) seen by the Hubble Space Telescope in 2010
 | discovery_ref   = &thinsp;<ref name="MPC-object"/><ref name="MPEC"/>
 | discoverer      = [[Biography:Megan Schwamb|Megan Schwamb]]<br />[[Biography:Michael E. Brown|Michael E. Brown]]<br />[[Biography:David L. Rabinowitz|David L. Rabinowitz]]
 | discovery_site  = [[Organization:Palomar Observatory|Palomar Obs.]]
 | discovered      = 17 July 2007&thinsp;{{efn|Discovery was announced two years later on 7 January 2009.}}
 | mpc_name        = {{mp|(225088) 2007 OR|10}}
 | alt_names       = {{mp|2007 OR|10}}
 | pronounced      = 
 | named_after     = 
 | mp_category     = {{nowrap|[[Astronomy:Trans-Neptunian object|TNO]]&thinsp;<ref name="jpldata"/>{{·}}[[Astronomy:Scattered disc|SDO]]&thinsp;<ref name="MPC-CEN-SDO-list"/><br />3:10 res.<ref name="Buie"/><ref name="johnstonsarchive-TNO-list"/>}}{{·}}[[Astronomy:List of possible dwarf planets|p-DP]]&thinsp;<ref name="Brown-dplist"/>
 | orbit_ref       = &thinsp;<ref name="jpldata"/>
 | epoch           = 27 April 2019 ([[Astronomy:Julian day|JD]] 2458600.5)
 | uncertainty     = 4
 | observation_arc = {{nowrap|30.09 yr (10,989 days)}}
 | earliest_precovery_date = 19 August 1985
 | aphelion        = 101.259 [[Astronomy:Astronomical unit|AU]]
 | perihelion      = 33.494 AU
 | semimajor       = 67.376 AU
 | eccentricity    = 0.503
 | period          = 553.05 [[Astronomy:Julian year|yr]] (202,003 days)
 | mean_anomaly    = 105.265[[Degree (angle)|°]]
 | mean_motion     = {{Deg2DMS|0.001782|sup=ms}} / day
 | inclination     = 30.739°
 | asc_node        = 336.844°
 | arg_peri        = 207.546°
 | satellites      = 1<ref name = "Lakdawalla2016a"/>
 | mean_diameter   = {{val|1230|50|ul=km}}<ref name="massdensity"/>
 | flattening      = 0.03 {{small|(for a rotation period of 22.4 h)}}<ref name="massdensity" /><br />0.007 {{small|(for a rotation period of 44.81 h)}}<ref name="massdensity" />
 | mass            = {{val|1.75|0.07|e=21|u=kg}}<ref name="massdensity"/>
 | density         = {{val|1.74|0.16|ul=g|up=cm3}}<ref name="massdensity"/>
 | surface_grav    = ≈&thinsp;{{Gr|1.75|615|2}}&thinsp;m/s<sup>2</sup>
 | escape_velocity = ≈&thinsp;{{V2|1.75|615|2}}&thinsp;km/s
 | rotation        = {{val|22.40|0.18|ul=h}} or {{val|44.81|0.37|ul=h}}<br />{{small|(ambiguous,<ref name="Pal-2016"/><ref name="scida2015"/> but 22.4 h more likely<ref name="massdensity"/>)}}
 | albedo          = {{val|0.14|0.01}}<ref name="massdensity"/>
 | spectral_type   = [[Astronomy:Trans-Neptunian object#Colors|B−V]]={{val|1.38|0.03}}<ref name="Boehnhardt-2014"/><ref name="lcdb"/><br />V−R={{val|0.86|0.02}}<ref name="Boehnhardt-2014"/><ref name="lcdb"/><br />V−I={{val|1.65|0.028}}<ref name="Boehnhardt-2014"/><ref name="lcdb"/>
 | magnitude       = {{val|21.5}}<ref name="AstDys"/>
 | abs_magnitude   = 2.34<ref name="Pal-2016"/>{{·}}2.0<ref name="Brown-dplist"/><br />1.8<ref name="jpldata"/>{{·}}1.6 (assumed)<ref name="MPC-object"/>
}}

'''{{mp|(225088) 2007 OR|10}}''', proposed to be named '''Gonggong''', is a likely [[Astronomy:List of possible dwarf planets|dwarf planet]] in the [[Astronomy:Solar System|Solar System]] beyond [[Astronomy:Neptune|Neptune]], and is a member of the [[Astronomy:Scattered disc|scattered disc]]. It has a highly [[Astronomy:Orbital eccentricity|eccentric]] and inclined orbit during which it ranges from {{convert|33|-|101|AU|e9km|abbr=off|lk=in|sp=us}} from the [[Astronomy:Sun|Sun]]. {{As of|2019}}, its distance from the Sun is {{cvt|88|AU}}, and it is the sixth-farthest known Solar System object. {{mp|2007 OR|10}} is in a 3:10 orbital resonance with Neptune, in which it completes three orbits around the Sun for every ten orbits completed by Neptune. {{mp|2007 OR|10}} was discovered in July 2007 by American astronomers [[Biography:Megan Schwamb|Megan Schwamb]], [[Biography:Michael E. Brown|Michael Brown]], and David Rabinowitz at the [[Organization:Palomar Observatory|Palomar Observatory]], and the discovery was announced in January 2009.

At {{convert|1230|km|mi|abbr=on}} in diameter, {{mp|2007 OR|10}} is approximately the size of Pluto's moon [[Astronomy:Charon (moon)|Charon]], and is the fifth-largest known trans-Neptunian object in the Solar System. It is sufficiently massive to be [[Astronomy:Hydrostatic equilibrium|gravitationally rounded]], thereby qualifying for dwarf planet status. Its large mass also makes retention of a tenuous [[Astronomy:Atmosphere|atmosphere]] of [[Chemistry:Methane|methane]] just possible, though such an atmosphere would slowly escape into space. {{mp|2007 OR|10}} is currently the largest known body in the [[Astronomy:Solar System|Solar System]] without an official name, but in 2019, the discoverers hosted an online poll for the general public to help choose a name for the object, and the name Gonggong won. The winning name is derived from Gonggong, a Chinese water god responsible for chaos, floods and the tilt of the Earth.

{{mp|2007 OR|10}} is red in color, likely due to the presence of organic compounds called [[Astronomy:Tholin|tholin]]s on its surface. Water [[Earth:Ice|ice]] is also present on its surface, which hints at a brief period of cryovolcanic activity in the distant past. {{mp|2007 OR|10}} rotates slowly compared to other trans-Neptunian objects, which typically have rotation periods less than 12 hours, which may be due to its [[Astronomy:Natural satellite|natural satellite]], provisionally designated S/2010 (225088) 1.

== History ==
=== Discovery ===
[[File:P48 1994 Jean Large.jpg|250px|thumb|left|{{mp|2007 OR|10}} was discovered using the Samuel Oschin telescope at Palomar Observatory]]
{{mp|2007 OR|10}} was discovered by American astronomers [[Biography:Megan Schwamb|Megan Schwamb]], [[Biography:Michael E. Brown|Michael Brown]] and [[Biography:David L. Rabinowitz|David Rabinowitz]] on 17 July 2007.<ref name="MPC-object"/> The discovery was part of the [[Astronomy:Palomar Distant Solar System Survey|Palomar Distant Solar System Survey]], a survey conducted to find distant objects in the region of {{dp|Sedna}}, beyond {{cvt|50|AU|lk=in}} from the [[Astronomy:Sun|Sun]], using the [[Astronomy:Samuel Oschin telescope|Samuel Oschin telescope]] at [[Organization:Palomar Observatory|Palomar Observatory]] near San Diego, {{wipe|California}}.<ref name="Schwamb2009"/><ref name="NeedsName"/><ref name="PalomarSurvey"/> The survey was designed to detect the movements of objects out to at least 1,000&nbsp;AU from the Sun.<ref name="PalomarSurvey"/> Schwamb identified {{mp|2007 OR|10}} by comparing multiple images using the [[Astronomy:Blink comparator#Modern replacements|blinking technique]].<ref name="NeedsName"/> In the discovery images, {{mp|2007 OR|10}} appeared to move slowly, suggesting that it is a distant object.<ref name="NeedsName"/><ref name="SomethingOutThere"/> The discovery was part of Schwamb's doctoral thesis. At that time, Schwamb was a graduate student of Michael Brown at the [[Organization:California Institute of Technology|California Institute of Technology]].<ref name="sciencedaily-2011"/><ref name="NeedsName"/>

{{mp|2007 OR|10}} was formally announced in a [[Organization:Minor Planet Center#Publications|Minor Planet Electronic Circular]] on 7 January 2009.<ref name="MPEC"/> It was then given the [[Astronomy:Provisional designation in astronomy|provisional designation]] {{mp|2007 OR|10}} because it was discovered during the second half of July 2007.<ref name="MPEC"/> The last letter and numbers of its designation indicate that it is the 267th object discovered during the latter half of July.{{efn|In the convention for minor planet provisional designation, the first letter represents the half-month of the year of discovery while the second letter and numbers indicate the order of discovery within that half-month. In the case for {{mp|2007 OR|10}}, the first letter 'O' corresponds to the second half-month of July 2007 while the last letter 'R' indicates that it is the 17th object discovered on the 10th cycle of discoveries. Each cycle consists of 25 letters representing discoveries, hence 17&thinsp;+&thinsp;(10 cycles × 25 letters)&thinsp;{{=}}&thinsp;267.<ref name="designation"/>}} {{As of|April 2017}}, it has been observed 230 times over 13 [[Astronomy:Opposition (planets)|oppositions]], and has been identified in two [[Astronomy:Precovery|precovery image]]s, with the earliest image taken by the La Silla Observatory on 19 August 1985.<ref name="MPC-object"/><ref name="precovery"/>
{{clear|left}}

=== Naming ===
{{As of|2019}}, {{mp|2007 OR|10}} is the largest known object in the Solar System without an official name.<ref name="NASA-news-2016"/> Initially after the discovery of {{mp|2007 OR|10}}, Brown nicknamed the object "Snow White" for its presumed white color based on his assumption that it may be a member of the icy Haumea collisional family.<ref name="BrownRedemption1"/><ref name="Brownblog"/> The nickname also fitted because, by that time, Brown's team had discovered seven other large trans-Neptunian objects which were collectively referred to as the "seven dwarfs":<ref name="Williams2015"/> {{dp|Quaoar}} in 2002, {{dp|Sedna}} in 2003, {{dp|Haumea}}, {{dp|Salacia}} and {{dp|Orcus}} in 2004, and {{dp|Makemake}} and {{dp|Eris}} in 2005. However, {{mp|2007 OR|10}} turned out to be very red in color, comparable to Quaoar, so the nickname was dropped.<ref name="BrownRedemption1"/><ref name="SomethingOutThere"/> On 2 November 2009, two years after its discovery, the [[Organization:Minor Planet Center|Minor Planet Center]] assigned the [[Astronomy:Minor planet number|minor planet number]] 225088 to {{mp|2007 OR|10}}.<ref name="precovery"/>

Upon the discovery and announcement of {{mp|2007 OR|10}}, Brown did not consider naming it, as he regarded it to be an unremarkable object, despite its large size.<ref name="Brownblog"/><ref name="Plotner2011"/> Brown later declared in 2011 that he now had enough information to justify giving it a name, in consideration of the discovery of water ice and the possibility of methane on its surface, which made it noteworthy enough to warrant further study.<ref name="sciencedaily-2011"/> Following the [[Astronomy:Kepler space telescope|''Kepler'']] spacecraft's large revision of {{mp|2007 OR|10}}'s size in 2016, Schwamb justified that {{mp|2007 OR|10}} was eligible for naming, an acknowledgement of its large size and that the characteristics of {{mp|2007 OR|10}} were known with enough certainty for a name to be given to reflect them.<ref name="NASA-news-2016"/>

In 2019, the discoverers of {{mp|2007 OR|10}} hosted an online poll for the general public to choose between three possible names: Gonggong (Chinese), [[Biology:Frau Holle|Holle]] (German), and [[Religion:Vili and Vé|Vili]] (Norse). These were selected by the discoverers in accordance with the [[Organization:International Astronomical Union|International Astronomical Union]]'s (IAU's) minor planet naming criteria, which state that objects with orbits like that of {{mp|2007 OR|10}} must be given names related to mythological figures that are associated with [[Astronomy:Creation myth|creation]].<ref name="naming"/><ref name="HowNamed"/> The three options were chosen because they were associated with water, ice, snow, and the color red—all characteristics of {{mp|2007 OR|10}}—and because they had associated figures that could later provide a name for {{mp|2007 OR|10}}'s satellite.<ref name="ann19021"/> The satellite would not be named by the hosts of the naming poll, as this privilege is reserved for its discoverers.<ref name="naming"/><ref name="results"/>

On 29 May 2019, the discovery team announced Gonggong as the winning name, it having gained 46 percent of the 280,000 votes casted.<ref name="results"/> The name has been proposed to the IAU's Committee on Small Body Nomenclature, which is responsible for naming minor planets.<ref name="results"/> In Chinese mythology, the water god Gonggong is depicted as having a red-haired human head and the body of a serpent. Gonggong was responsible for creating chaos, causing flooding, and tilting the Earth, and was sent into exile.<ref name="naming"/><ref name="results"/>

== Physical characteristics ==
=== Surface and spectra ===
[[File:Snow2whi.jpg|upright|thumb|Artist's impression of {{mp|2007 OR|10}} depicting its red surface color]]
The surface of {{mp|2007 OR|10}} has an [[Earth:Albedo|albedo]] (reflectivity) of 0.14.<ref name="massdensity"/> The surface composition and spectrum of {{mp|2007 OR|10}} is expected to be similar to that of {{dp|Quaoar}}, as both objects are red in color and display signs of [[Earth:Ice|water ice]] and possibly [[Chemistry:Methane|methane]] in their spectra.<ref name="kbcomp"/><ref name="TNOsCool4"/> The [[Physics:Reflectance|reflectance]] spectrum of {{mp|2007 OR|10}} was first measured in 2011 at near-infrared [[Wavelength|wavelength]]s, with the Folded port InfraRed Echellette (FIRE) [[Astronomy:Spectrograph|spectrograph]] on the [[Astronomy:Magellan Telescopes|Magellan Baade Telescope]] at the Las Campanas Observatory in {{wipe|Chile}}.<ref name="Brown-2011"/> {{mp|2007 OR|10}}'s spectrum exhibits a strong red [[Spectral slope|spectral slope]] along with broad [[Physics:Absorption band|absorption band]]s at wavelengths of 1.5&nbsp;[[Micrometre|μm]] and 2&nbsp;μm, meaning that {{mp|2007 OR|10}} reflects more light at these wavelengths.<ref name="Brown-2011"/> Additional [[Astronomy:Photometry|photometric]] measurements from the [[Astronomy:Hubble Space Telescope|Hubble Space Telescope]]'s [[Engineering:Wide Field Camera 3|Wide Field Camera 3]] instrument display similar absorption bands at 1.5&nbsp;μm,<ref name="Brown-2011"/> which are characteristic features of water ice, a substance often found on large Kuiper belt objects.<ref name="kbowater"/> The presence of water ice on the surface of {{mp|2007 OR|10}} implies a brief period of cryovolcanism in the distant past, when water erupted from its interior, deposited onto its surface, and subsequently froze.<ref name="BrownRedemption3"/>

{{mp|2007 OR|10}} is among the [[Astronomy:Trans-Neptunian object#Colors|reddest]] trans-Neptunian objects known, especially in the visible and near-infrared.<ref name="Brown-2011"/><ref name="Boehnhardt-2014"/> Its red color is unexpected for an object with a substantial amount of water ice on its surface,<ref name="BrownRedemption3"/><ref name="sciencedaily-2011"/> which are typically neutral in color, hence why {{mp|2007 OR|10}} was initially nicknamed "Snow White".<ref name="BrownRedemption1"/><ref name="Brownblog"/> {{mp|2007 OR|10}}'s color implies that methane is present on its surface, although it was not directly detected in the spectrum of {{mp|2007 OR|10}} due to the low [[Physics:Signal-to-noise ratio|signal-to-noise ratio]] of the data.<ref name="Brown-2011"/> The presence of methane frost would account for its red color, as a result of the photolysis of methane by solar radiation and [[Astronomy:Cosmic ray|cosmic ray]]s producing reddish [[Chemistry:Organic compound|organic compound]]s known as [[Astronomy:Tholin|tholin]]s.<ref name="Brown-2011"/><ref name="Pal-2016"/> Observations of {{mp|2007 OR|10}}'s near-infrared spectrum in 2015 revealed an absorption feature at 2.27&nbsp;μm, indicating the presence of [[Chemistry:Methanol|methanol]] along with its irradiation products on its surface.<ref name="Holler2017"/> Methanol is expected to brighten {{mp|2007 OR|10}}'s surface, although the irradiation of water ice may account for its present dark surface.<ref name="Holler2017"/>

{{mp|2007 OR|10}} is large enough to be able to retain trace amounts of [[Chemistry:Volatility|volatile]] methane on its surface,<ref name="Brown-2011"/> even when at its closest distance to the Sun (33.5&nbsp;[[Astronomy:Astronomical unit|AU]]),<ref name="jpldata"/> where temperatures are higher than that of Quaoar.<ref name="Brown-2011"/> In particular, the large size of {{mp|2007 OR|10}} means that it is likely to retain trace amounts of other volatiles, including [[Chemistry:Ammonia|ammonia]], [[Chemistry:Carbon monoxide|carbon monoxide]], and possibly [[Chemistry:Nitrogen|nitrogen]], which almost all trans-Neptunian objects lose over the course of their existence.<ref name="kbcomp"/><ref name="Pal-2016"/><ref name="NASA-news-2016"/> Like Quaoar, {{mp|2007 OR|10}} is expected to be near the mass limit at which it is able to retain those [[Astronomy:Volatiles|volatile materials]] on its surface.<ref name="kbcomp"/><ref name="sciencedaily-2011"/>

=== Atmosphere ===
The presence of tholins on the surface of {{mp|2007 OR|10}} implies the possible existence of a tenuous methane atmosphere, analogous to Quaoar.<ref name="BrownRedemption3"/><ref name="sciencedaily-2011"/> Although {{mp|2007 OR|10}} occasionally comes closer to the Sun than Quaoar, where it becomes warm enough that a methane atmosphere should evaporate, its larger mass could make the retention of methane just possible.<ref name="Brown-2011"/> During aphelion, methane along with other [[Astronomy:Volatiles|volatiles]] would condense on {{mp|2007 OR|10}}'s surface, allowing for long-term irradiation that would otherwise result in a decrease in surface albedo.<ref name="Johnson2015"/> The lower surface albedo would contribute to the loss of highly volatile materials such as nitrogen, as a lower albedo corresponds to more light being [[Physics:Absorption (electromagnetic radiation)|absorbed]] by the surface rather than being reflected, thus resulting in greater surface heating. Hence, the nitrogen content of {{mp|2007 OR|10}}'s atmosphere is expected to be depleted to trace amounts while methane is likely retained.<ref name="Johnson2015"/>

{{mp|2007 OR|10}} is thought to have had cryovolcanic activity along with a more substantial atmosphere shortly after its [[Astronomy:Formation and evolution of the Solar System|formation]].<ref name="BrownRedemption3"/><ref name="sciencedaily-2011"/> Such cryovolcanic activity is expected to have been brief, and the resulting atmosphere gradually [[Earth:Atmospheric escape|escaped]] over time.<ref name="BrownRedemption3"/><ref name="sciencedaily-2011"/> Volatile gases, such as nitrogen and carbon monoxide, were lost, while less volatile gases such as methane are likely to remain in its present tenuous atmosphere.<ref name="BrownRedemption3"/><ref name="Johnson2015"/>

=== Size ===
{| class="wikitable floatleft" style="text-align: center; font-size: 0.9em; margin-right: 12px;"
|+ Size estimates
|-
! Year !! Diameter !! Method !! Refs
|-
| 2010
| 1,752&nbsp;km
| thermal
| <ref name="Tancredi2010"/>
|-
| 2011
| {{val|1200|300|200|fmt=commas|u=km}}
| best fit albedo
| <ref name="Brown-2011"/>
|-
| 2012
| {{val|1280|210|fmt=commas|u=km}}
| thermal
| <ref name="TNOsCool4"/>
|-
| 2013
| {{val|1142|647|467|fmt=commas|u=km}}
| thermal
| <ref name="TNOsCool9"/>
|-
| 2013
| 1,290&nbsp;km
| radiometric
| <ref name="Brown-dplist"/>
|-
| 2016
| {{val|1535|75|225|fmt=commas|u=km}}
| thermal
| <ref name="Pal-2016"/>
|-
| 2018
| {{val|1230|50|fmt=commas|u=km}}
| radiometric
| <ref name="massdensity"/>
|}
{{TNO imagemap}}
[[File:2007 OR10, Earth & Moon size comparison.png|upright|thumb|{{mp|2007 OR|10}} compared to the Earth and the Moon]]
As of 2019, {{mp|2007 OR|10}} is estimated to have a diameter of {{convert|1230|km|mi|abbr=on}}, derived from [[Astronomy:Radiometry|radiometric]] measurements, its calculated mass, and assuming a density similar to other similar bodies.<ref name="massdensity"/> This would make {{mp|2007 OR|10}} the fifth-largest trans-Neptunian object, after [[Astronomy:Pluto|Pluto]], [[Astronomy:Eris (dwarf planet)|Eris]], [[Astronomy:Haumea|Haumea]] and [[Astronomy:Makemake|Makemake]]. {{mp|2007 OR|10}} is approximately the size of Pluto's moon [[Astronomy:Charon (moon)|Charon]], although {{mp|2007 OR|10}}'s current size estimate has an uncertainty of {{convert|50|km|mi|abbr=on}}.<ref name="massdensity"/>

The International Astronomical Union (IAU) has not addressed the possibility of officially accepting additional dwarf planets since the acceptance of [[Astronomy:Makemake|Makemake]] and [[Astronomy:Haumea|Haumea]] in 2008, prior to the announcement of {{mp|2007 OR|10}} in 2009.<ref name="IAU-naming"/><ref name="IAU0603"/> Despite not satisfying the IAU's criterion of having an [[Astronomy:Absolute magnitude#Solar System bodies (H)|absolute magnitude]] brighter than +1,<ref name="IAU-naming"/>{{efn|A larger magnitude value corresponds to a dimmer brightness and vice versa. The numerical value of {{mp|2007 OR|10}}'s absolute magnitude is 2.34,<ref name="Pal-2016"/> hence it is dimmer than the IAU's minimum absolute magnitude of 1.}} {{mp|2007 OR|10}} is large enough to be considered a dwarf planet by several astronomers.<ref name="Tancredi2010"/><ref name="Sheppard-2011"/><ref name="Brown-dplist"/> Brown states that {{mp|2007 OR|10}} "must be a dwarf planet even if predominantly rocky", based on the 2013 radiometric measurement of {{val|1290|u=km}}.<ref name="Brown-dplist"/> [[Biography:Scott S. Sheppard|Scott Sheppard]] and his colleagues think that it is likely to be a dwarf planet,<ref name="Sheppard-2011"/> based on its minimum possible diameter—{{val|580|u=km}} under the assumption of an albedo of 1{{refn|The resulting minimum diameter of 580&nbsp;km is derived from the equation <math> E=\frac{1329}{\sqrt{p}} 10^{-0.2H}</math>, where <math>H</math> is the absolute magnitude of {{mp|2007 OR|10}}, and <math>p</math> is the albedo of {{mp|2007 OR|10}}, which in this case is assumed to be 1.<ref name="sizemagnitude"/>|name=magnitude|group=lower-alpha}}—and what was at the time the expected lower size limit of around {{val|200|u=km}} for [[Astronomy:Hydrostatic equilibrium|hydrostatic equilibrium]] in cold icy-rocky bodies.<ref name="Sheppard-2011"/> However, Iapetus is not in equilibrium despite being {{convert|1470|km|mi|abbr=on}} in diameter, so this remains just a possibility.<ref name="Thomas2010">{{cite journal| doi = 10.1016/j.icarus.2010.01.025| last1 = Thomas| first1 = P. C.| date = July 2010| title = Sizes, shapes, and derived properties of the saturnian satellites after the Cassini nominal mission| journal = Icarus| volume = 208| issue = 1| pages = 395–401| pmid = | pmc = | url = http://www.ciclops.org/media/sp/2011/6794_16344_0.pdf| bibcode = 2010Icar..208..395T| ref = harv}}</ref>

In 2010, astronomer Gonzalo Tancredi initially estimated {{mp|2007 OR|10}} to have a very large diameter of {{convert|1752|km|mi|abbr=on}}, though its dwarf planet status was unclear as there was no lightcurve data or other information to ascertain its size.<ref name="Tancredi2010"/> {{mp|2007 OR|10}} is too distant to be resolved directly; Brown placed a rough estimate of its diameter ranging from {{convert|1000|-|1500|km|mi|abbr=on}}, based on an albedo of 0.18 which was the best fit in his model.<ref name="Brown-2011"/> A survey led by a team of astronomers using the [[Organization:European Space Agency|European Space Agency]]'s [[Astronomy:Herschel Space Observatory|Herschel Space Observatory]] in 2012 determined its diameter to be {{val|1280|210|u=km}}, based on the thermal properties of {{mp|2007 OR|10}} observed in the [[Physics:Far infrared|far infrared]] range.<ref name="TNOsCool4"/> This measurement is consistent with Brown's estimate. Later observations in 2013 using combined thermal emission data from ''Herschel'' and the [[Astronomy:Spitzer Space Telescope|Spitzer Space Telescope]] suggested a smaller size of {{val|1142|647|467|u=km}}, though this estimate had a larger range of uncertainty.<ref name="TNOsCool9"/>

In 2016, combined observations from the [[Astronomy:Kepler space telescope|''Kepler'']] spacecraft and archival thermal emission data from ''Herschel'' suggested that {{mp|2007 OR|10}} was much larger than previously thought, giving a size estimate of {{val|1535|75|225|u=km}} ({{val|954|u=mi}}) based on an assumed equator-on view and a lower estimated albedo of 0.089.<ref name="Pal-2016"/><ref name="scida2015"/> This would have made {{mp|2007 OR|10}} the third-largest trans-Neptunian object after Eris and Pluto, larger than Makemake ({{val|1430|u=km}}).<ref name="scida2015"/><ref name="NASA-news-2016"/> These observations of {{mp|2007 OR|10}} were part of the ''Kepler'' spacecraft's [[Astronomy:Kepler space telescope#Second Light (K2)|K2 mission]] which includes studying [[Astronomy:Small Solar System bodies|small Solar System bodies]].<ref name="NASA-news-2016"/> Subsequent measurements in 2018 revised the size of {{mp|2007 OR|10}} to {{val|1230|50|u=km}}, based on the mass and density of {{mp|2007 OR|10}} derived from the orbit of its satellite and the discovery that the viewing direction was almost [[Astronomy:Axial tilt|pole-on]].<ref name="massdensity"/> With this size estimate, {{mp|2007 OR|10}} is again thought to be the fifth-largest trans-Neptunian object.<ref name="massdensity"/>

=== Mass, density and rotation ===
[[File:Kepler 2007 OR10.ogg|thumb|{{mp|2007 OR|10}} moving among background stars during a 19-day observation period by the ''Kepler'' spacecraft<ref name="NASA-news-2016"/>]]
Based on the orbit of its satellite, the mass of {{mp|2007 OR|10}} has been calculated to be {{cvt|1.75e21|kg|lbs}}, with a density of {{val|1.72|0.16|u=g/cm3}}.<ref name="massdensity"/> From these mass and density estimates, the size of {{mp|2007 OR|10}} was calculated to be about {{convert|1230|km|mi|abbr=on}}, smaller than the previous 2016 size estimate of {{convert|1535|km|mi|abbr=on}}.<ref name="massdensity"/> Given the mass, the 2016 size estimate of {{convert|1535|km|mi|abbr=on}} would have implied an unexpectedly low (and likely erroneous) density of {{val|0.92|u=g/cm3}}.<ref name="massdensity"/>

{{mp|2007 OR|10}} is the fifth most massive trans-Neptunian object, after Eris, Pluto, Haumea, and Makemake.<ref name="massdensity"/> It is slightly more massive and denser than Charon, which has a mass of {{cvt|1.586e21|kg|lbs}} and a density of {{val|1.702|u=g/cm3}}.<ref name="massdensity"/><ref name="Stern_2017"/> Due to its large size, mass, and density, {{mp|2007 OR|10}} is expected to be in hydrostatic equilibrium, taking the shape of a MacLaurin spheroid that is slightly flattened due to its rotation.<ref name="massdensity"/><ref name="Pal-2016"/>

The rotation period of {{mp|2007 OR|10}} was first measured in March 2016, through observations of variations in its brightness with the ''Kepler'' space telescope.<ref name="Pal-2016"/> {{mp|2007 OR|10}}'s [[Astronomy:Light curve|light curve]] [[Physics:Amplitude|amplitude]] as observed by ''Kepler'' is small, only varying in brightness by about 0.09 [[Astronomy:Magnitude|magnitude]]s.<ref name="Pal-2016"/> The small light curve amplitude of {{mp|2007 OR|10}} indicates that it is being viewed at a pole-on configuration, further evidenced by the observed inclined orbit of its satellite.<ref name="massdensity"/> The ''Kepler'' observations provided ambiguous values of {{val|44.81|0.37}} and {{val|22.4|0.18}} hours for the rotation period.<ref name="Pal-2016"/><ref name="massdensity"/> Based on a best-fit model for its rotation pole orientation, the value of {{val|22.4|0.18}} hours is thought to be the more plausible one.<ref name="massdensity"/> {{mp|2007 OR|10}} rotates slowly compared to other trans-Neptunian objects, which usually have rotation periods between 6 and 12 hours.<ref name="massdensity"/> Due to its slow rotation, it is expected to have a low oblateness of 0.03 or 0.007, for rotation periods of 22.4 or 44.81 hours, respectively.<ref name="massdensity"/>

== Orbit ==
{{multiple image
 |direction=horizontal
 |align=right
 |width1=187
 |width2=233
 |width3=270
 |image1=2007 OR10 orbit Jan2018.png
 |image2=2007 OR10 orbit Jan2018-side.png
 |image3=TNO-2007OR10-resonance.gif
 |caption1=Polar view of the orbits of {{mp|2007 OR|10}}, [[Astronomy:Eris (dwarf planet)|Eris]], and [[Astronomy:Pluto|Pluto]]
 |caption2=[[Astronomy:Ecliptic|Ecliptic]] view of the highly inclined orbits of {{mp|2007 OR|10}} and Eris
 |caption3=A preliminary motion analysis of {{mp|2007 OR|10}} librating in a 3:10 resonance with Neptune. This animation consists of 16 frames covering 26,000 years.<ref name="Buie"/> Neptune (white dot) is held stationary.}}
[[File:2007OR10 star path.png|thumb|400px|Apparent motion of {{mp|2007 OR|10}} through the constellation [[Astronomy:Aquarius (constellation)|Aquarius]] (years 2000 to 2050)]]

{{mp|2007 OR|10}} orbits the Sun at an average distance of {{cvt|67.4|AU}}, and completes a full orbit in 553 years.<ref name="jpldata"/> The orbit of {{mp|2007 OR|10}} is highly inclined to the [[Astronomy:Ecliptic|ecliptic]], with an [[Astronomy:Orbital inclination|orbital inclination]] 30.7 degrees.<ref name="jpldata"/> Its orbit is also highly eccentric, with a measured [[Astronomy:Orbital eccentricity|orbital eccentricity]] of 0.503.<ref name="jpldata"/> Due to its highly eccentric orbit, the distance of {{mp|2007 OR|10}} from the Sun varies greatly over the course of its orbit, from {{cvt|101.3|AU}} at aphelion, its furthest point from the Sun, to around {{cvt|33.5|AU}} at perihelion, its closest point to the Sun.<ref name="jpldata"/><ref name="MPC-object"/> {{mp|2007 OR|10}} had approached its perihelion in 1857, and is currently moving farther from the Sun, toward its aphelion.<ref name="theskylive"/>

The [[Organization:Minor Planet Center|Minor Planet Center]] lists it as a [[Astronomy:Scattered disc|scattered disc]] object for its eccentric and distant orbit.<ref name="MPC-CEN-SDO-list"/> The [[Astronomy:Deep Ecliptic Survey|Deep Ecliptic Survey]] shows the orbit of {{mp|2007 OR|10}} to be in a 3:10 resonance with Neptune; {{mp|2007 OR|10}} completes three orbits around the Sun for every ten orbits completed by Neptune.<ref name="Buie"/>

{{asof|2019}}, {{mp|2007 OR|10}} is about {{convert|88|AU|km|lk=in|abbr=on}} from the Sun<ref name="AstDyS-distances"/> and is moving away at a speed of {{convert|1.1|km/s|mph|abbr=off|sp=us}}.<ref name="horizons"/> It is the sixth-farthest known Solar System object from the Sun, preceding {{mpl|2015 TH|367}} (89.5&nbsp;AU), {{mpl|2014 UZ|224}} (90.4&nbsp;AU), {{dp|Eris}} (96.1&nbsp;AU), {{mpl|2018 VG|18}} (~&thinsp;120&nbsp;AU),<ref name="2018VG18"/> and "[[Astronomy:FarFarOut|FarFarOut]]" (~&thinsp;140&nbsp;AU).<ref name="AstDyS-distances"/><ref name="farfarout"/> {{mp|2007 OR|10}} is more distant than {{dp|Sedna}}, which is located 84.8&nbsp;AU from the Sun as of July 2019.<ref name="AstDyS-distances"/> It has been farther from the Sun than Sedna since 2013.<ref name="horizons"/> {{mp|2007 OR|10}} will be farther than both Sedna and Eris by 2045,<ref name="Horizons2076"/> and will reach its aphelion in 2130.<ref name="horizons"/>

=== Brightness ===
{{mp|2007 OR|10}} has an absolute magnitude (H) of 2.34,<ref name="Boehnhardt-2014"/><ref name="Pal-2016"/> which makes it the seventh-brightest trans-Neptunian object known. It is dimmer than {{dp|Orcus}} (H=2.31; D=917&nbsp;km)<ref name="TNOsCool8"/> but brighter than Quaoar (H=2.82; D=1,110&nbsp;km).<ref name="Braga-Ribas-2013"/> The Minor Planet Center and the [[Astronomy:JPL Small-Body Database|Jet Propulsion Laboratory Small-Body Database]] assume a brighter absolute magnitude of 1.6 and 1.8, respectively,<ref name="MPC-object"/><ref name="jpldata"/> which would make it the fifth brightest trans-Neptunian object.<ref name="BrownRedemption2"/>

Being 88&nbsp;AU from the Sun, the [[Astronomy:Apparent magnitude|apparent magnitude]] of {{mp|2007 OR|10}} is only 21.5,<ref name="AstDys"/> and so it is too dim to be seen from [[Astronomy:Earth|Earth]] with the [[Astronomy:Naked eye|naked eye]].<ref name="naming"/>{{efn|Under good conditions, the unaided human eye can detect objects with a visual magnitude of around +7.4 or lower.<ref>{{cite web|title=What's my naked-eye magnitude limit?|url=https://www.skyandtelescope.com/astronomy-resources/astronomy-questions-answers/naked-eye-magnitude-limit/|first=Roger W.|last=Sinnott|publisher=Sky and Telescope|date=19 July 2006|accessdate=17 April 2019}}</ref>}} Although closer to the Sun than the dwarf planet Eris, {{mp|2007 OR|10}} appears dimmer, as Eris has a higher albedo and an apparent magnitude of 18.8.<ref name="TNOsCool4"/><ref name="Astdys_Eris"/>

== Satellite ==
[[File:Moon Around the Dwarf Planet 2007 OR10.jpg|thumb|Hubble images of {{mp|2007 OR|10}} and its moon, taken in 2009 and 2010 with the Wide Field Camera 3]]
Following the March 2016 discovery that {{mp|2007 OR|10}} was an unusually slow rotator, the possibility was raised that a satellite may have slowed it down via [[Physics:Tidal force|tidal force]]s.<ref name="Lakdawalla2016a"/> The indications of a possible satellite orbiting {{mp|2007 OR|10}} led Csaba Kiss and his team to analyze [[Astronomy:Precovery|archival]] Hubble observations of {{mp|2007 OR|10}}.<ref name="Kissetal2017"/> Their analysis of Hubble images taken on 18 September 2010 revealed a faint satellite orbiting {{mp|2007 OR|10}} at a distance of at least {{convert|15000|km|mi|abbr=on}}.<ref name="DPS48"/> The discovery was announced on 17 October 2016 and the satellite was subsequently [[Astronomy:Provisional designation|provisionally designated]] S/2010 (225088) 1.<ref name="naming"/> The satellite is approximately {{convert|100|km|mi|abbr=on}} in diameter and has an orbital period of 25 days.<ref name="Kissetal2017"/>

== Exploration ==
It was calculated by [[Astronomy:Planetary science|planetary scientist]] Amanda Zangari that a [[Engineering:Flyby (spaceflight)|flyby]] mission to {{mp|2007 OR|10}} would take a minimum of over 20 years with current rocket capabilities.<ref name="Zangari2018"/> A flyby mission could take just under 25 years using a Jupiter [[Astronomy:Gravity assist|gravity assist]], based on a launch date of 2030 or 2031. {{mp|2007 OR|10}} would be approximately 95 AU from the Sun when the spacecraft arrives.<ref name="Zangari2018"/>

== See also ==
* List of gravitationally rounded objects of the Solar System
* [[Astronomy:List of most distant trans-Neptunian objects|List of most distant trans-Neptunian objects]]
* List of Solar System objects most distant from the Sun
* [[Astronomy:List of possible dwarf planets|List of possible dwarf planets]]

== Notes ==
{{notelist}}

== References ==
{{Reflist|30em|refs=

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<ref name="sciencedaily-2011">{{cite news
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<ref name="NeedsName">{{cite web
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  |publisher  = International Astronomical Union
  |date       = 10 April 2019
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<ref name="lcdb">{{cite web
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  |arxiv      = 1810.07811}}</ref>
  
<ref name="theskylive">{{cite web
  |url        = https://theskylive.com/2007or10-info
  |title      = Asteroid 2007 OR10
  |publisher  = The Sky Live
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<ref name="AstDyS-distances">{{cite web
  |title      = AstDyS-2, Asteroids - Dynamic Site
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  |work       = Asteroids Dynamic Site
  |publisher  = Department of Mathematics, University of Pisa
  |quote      = Objects with distance from Sun over 84.2 AU
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<ref name="horizons">{{cite web
  |title      = Horizon Online Ephemeris System
  |type       = Settings: Ephemeris Type "VECTORS", Table Settings "output units=KM-S"
  |url        = http://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&body_group=sb&sstr=2007OR10
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<ref name="2018VG18">{{cite news
  |title      = Discovered: The Most-Distant Solar System Object Ever Observed
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  |title      = Astronomers Discover Solar System's Most Distant Object, Nicknamed 'FarFarOut'
  |work       = Science
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  |date       = 21 February 2019
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<ref name="designation">{{cite web
  |title      = New- And Old-Style Minor Planet Designations
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  |work       = Minor Planet Center
  |publisher  = International Astronomical Union
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  |work       = Andrew Lowe's Minor Planet Home Page
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  |title      = Help Name 2007 OR10
  |url        = https://2007or10.name
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<ref name="results">{{cite web
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<ref name="IAU-naming">{{cite web
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<ref name="Williams2015">{{cite web
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<ref name="Braga-Ribas-2013">{{cite journal
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<ref name="Holler2017">{{cite conference
  |title      = Methanol ice on Kuiper Belt objects 2007 OR<sub>10</sub> and Salacia: Implications for formation and dynamical evolution
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  |publisher  = European Planetary Science Congress
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  |id         = EPSC2017-330
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}} <!-- end of reflist -->

== External links ==
* [http://andrew-lowe.ca/2007or10.htm {{mp|2007 OR|10}} Precovery Images]
* [http://www.cfa.harvard.edu/mpec/K09/K09V05.html {{mp|2007 OR|10}} Minor planet designation number]
* [https://hla.stsci.edu/hlaview.html#Inventory|filterText%3D%24filterTypes%3D|query_string=22%2016%2030.29%20%20%20-14%2024%2045.5&posfilename=&poslocalname=&posfilecount=&listdelimiter=whitespace&listformat=degrees&RA=334.126208&Dec=-14.412639&Radius=0.200000&inst-control=all&inst=ACS&inst=ACSGrism&inst=WFC3&inst=WFPC2&inst=NICMOS&inst=NICGRISM&inst=COS&inst=WFPC2-PC&inst=STIS&inst=FOS&inst=GHRS&imagetype=best&prop_id=&spectral_elt=&proprietary=both&preview=1&output_size=256&cutout_size=12.8|ra=&dec=&sr=&level=&image=&inst=ACS%2CACSGrism%2CWFC3%2CWFPC2%2CNICMOS%2CNICGRISM%2CCOS%2CWFPC2-PC%2CSTIS%2CFOS%2CGHRS&ds= Hubble images of (225088) {{mp|2007 OR|10}} taken on 18 September 2010]
* [https://hla.stsci.edu/hlaview.html#Inventory|filterText%3D%24filterTypes%3D|query_string=22%2022%2000%20-12%2034%2042%20r%3D5d&posfilename=&poslocalname=&posfilecount=&listdelimiter=whitespace&listformat=degrees&RA=335.500000&Dec=-12.578333&Radius=5.000000&inst-control=all&inst=ACS&inst=ACSGrism&inst=WFC3&inst=WFPC2&inst=NICMOS&inst=NICGRISM&inst=COS&inst=WFPC2-PC&inst=STIS&inst=FOS&inst=GHRS&imagetype=best&prop_id=15207&spectral_elt=&proprietary=both&preview=1&output_size=256&cutout_size=12.8|ra=&dec=&sr=&level=&image=&inst=ACS%2CACSGrism%2CWFC3%2CWFPC2%2CNICMOS%2CNICGRISM%2CCOS%2CWFPC2-PC%2CSTIS%2CFOS%2CGHRS&ds= Hubble images of (225088) {{mp|2007 OR|10}} taken in 2017]
* [http://www.mikebrownsplanets.com/2011/08/redemption-of-snow-white-part-1.html The redemption of Snow White (Part 1)] (Mike Brown blog 9 August 2011)
* [https://www.minorplanetcenter.net/iau/lists/NumberedMPs225001.html Discovery Circumstances: Numbered Minor Planets (225001)-(230000)] – Minor Planet Center
* [https://www.wired.com/2016/05/give-dwarf-planet-2007-or10-real-name-deserves-already Give Dwarf Planet 2007 OR10 the Real Name It Deserves Already] – WIRED article by Emma Grey Ellis
* {{AstDys|225088}}
* {{JPL small body}}

{{Dwarf planets}}
{{Trans-Neptunian objects}}
{{Minor planets navigator | |number=225088 |PageName={{mp|(225088) 2007 OR|10}} | }}
{{Small Solar System bodies}}

{{DEFAULTSORT:2007 OR10}}
[[Category:Possible dwarf planets|225088]]

{{Sourceattribution|(225088) 2007 OR10|1}}