Просмотр кода страницы Английская Википедия:(307261) 2002 MS4

{{Английская Википедия/Панель перехода}}
{{Short description|Classical Kuiper belt object}}
{{DISPLAYTITLE:{{mp|(307261) 2002 MS|4}}}} <!-- DISCLAIMER: The page numbers listed in the {{rp|page=}} templates refer to the actual publication page number, not the PDF page number -->
{{Infobox planet
 | minorplanet     = yes
 | name            = {{mp|(307261) 2002 MS|4}}
 | background      = #C2E0FF
 | image           = 2002MS4_Hubble.png
 | image_size      = 250
 | caption         = {{mp|2002 MS|4}} imaged by the [[Hubble Space Telescope]] on 9 April 2006
 | discovery_ref   = <ref name="MPC-object"/>
 | discovered      = 18 June 2002
 | discoverer      = [[Chad Trujillo|Chadwick A. Trujillo]]<br/>[[Michael E. Brown]]
 | discovery_site  = [[Palomar Observatory|Palomar Obs.]]
 | mpc_name        = {{mp|2002 MS|4}}
 | alt_names       = 
 | pronounced      = 
 | named_after     = 
 | mp_category     = {{Nowrap|[[Trans-Neptunian object|TNO]]<ref name="jpldata"/>{{·}}[[Classical Kuiper belt object|cubewano]] (hot)<ref name="Gladman2008"/>{{rp|page=56}}}}<br/>[[Distant minor planet|distant]]<ref name="MPC-object"/>{{·}}[[Scattered disc|Scat-Ext]]<ref name="Buie"/>
 | orbit_ref       = <ref name="horizons-ssb"/><ref name="jpldata"/>
 | barycentric     = yes
 | epoch           = 25 February 2023 ([[Julian day|JD]] 2460000.5)
 | uncertainty     = 2
 | observation_arc = 66.22 yr (24,188 d)
 | earliest_precovery_date = 8 April 1954
 | aphelion        = 47.801 [[Astronomical unit|AU]]
 | perihelion      = 35.677 AU
 | time_periastron = ≈ 10 June 2123<ref name="perihelion-2123"/><br />±0.6 days<ref name="jpldata"/>
 | semimajor       = 41.739 [[Astronomical unit|AU]]
 | eccentricity    = 0.14524
 | period          = 269.48 [[Julian year (astronomy)|yr]] (98,429 [[Julian year (astronomy)|d]])
 | mean_anomaly    = 226.844[[Degree (angle)|°]]
 | mean_motion     = {{Deg2DMS|0.0036575|sup=ms}} / day
 | inclination     = 17.693°
 | asc_node        = 216.075°
 | arg_peri        = 214.575°
 | dimensions      = ({{val|823|20}})&nbsp;×&nbsp;({{val|770|34}})&nbsp;km (projected)<ref name="Rommel2023"/>
 | mean_diameter   = {{val|796|24|u=km}}<ref name="Rommel2023"/>
 | flattening      = {{val|0.066|0.034|p=≥}}<ref name="Rommel2023"/>{{rp|page=5}}
 | mass            = 
 | density         = 
 | rotation        = {{val|14.251|ul=h}}<ref name="Peng2023"/>{{rp|pages=5, 54}}<br/>{{val|7.33|u=h}} or {{val|10.44|u=h}} (single-peaked)<ref name="Thirouin2013"/>{{rp|page=158}}
 | albedo          = {{val|0.100|0.025}}<ref name="Rommel2023"/>{{rp|page=8}} or {{val|0.098|0.004}}<ref name="Verbiscer2022"/>{{rp|page=2}}&nbsp;([[Geometric albedo|geometric]])<br/>{{val|0.039|0.005}} ([[Bond albedo|Bond]])<ref name="Verbiscer2022"/>{{rp|page=23}}
 | spectral_type   = [[Trans-Neptunian object#Color indices|B−V]]={{val|0.69|0.02}}<ref name="Tegler2016"/>{{rp|page=6}}<br/>V−R={{val|0.38|0.02}}<br/>B−R={{val|1.07|0.02}}
 | abs_magnitude   = {{val|3.56|0.03}}<ref name="Peng2023"/>{{rp|pages=62, 74}}<br/>{{val|3.63|0.05}}<ref name="Rommel2023"/>{{rp|page=8}}<br/>3.62<ref name="jpldata"/><ref name="MPC-object"/>
 | magnitude       = 20.5<ref name="AstDys"/>
 | single_temperature = 65 [[kelvin|K]]<ref name="Cook2023-eposter"/>
}}

'''{{mp|(307261) 2002 MS|4}}''' ([[provisional designation]] '''{{mp|2002 MS|4}}''') is a large [[trans-Neptunian object]] in the [[Kuiper belt]], a region of icy [[planetesimal]]s beyond [[Neptune]]. It was discovered on 18 June 2002 by [[Chad Trujillo]] and [[Michael E. Brown|Michael Brown]] during their search for bright, [[Pluto]]-sized Kuiper belt objects at [[Palomar Observatory]]. {{mp|2002 MS|4}} has a diameter close to {{cvt|800|km|mi}}, which approximately ties it with {{mpl|2002 AW|197}} and {{mpl|2013 FY|27}} (to within measurement uncertainties) as the [[List of Solar System objects by size|largest unnamed object]] in the Solar System. {{mp|2002 MS|4}} is large enough that astronomers consider it a [[List of possible dwarf planets|possible dwarf planet]].

The surface of {{mp|2002 MS|4}} is dark gray and is composed of water and [[carbon dioxide]] ices. {{mp|2002 MS|4}} has been observed through [[stellar occultation]]s, which have revealed massive topographic features along the outline of its shape. These features include a mountain-like peak that is {{cvt|25|km|mi}} tall and a [[crater]]-like depression that is {{cvt|320|km|mi}} wide and {{cvt|45|km|mi}} deep. {{mp|2002 MS|4}}'s topographic features are among the [[List of tallest mountains in the Solar System|tallest]] and deepest known for Solar System bodies.

== History ==
=== Discovery ===
{{mp|2002 MS|4}} was discovered on 18 June 2002 by astronomers [[Chad Trujillo]] and [[Michael E. Brown|Michael Brown]] at [[Palomar Observatory]] in [[San Diego County, California]], United States.<ref name="MPC-object"/> The discovery formed part their Caltech Wide Area Sky Survey for bright, [[Pluto]]-sized [[Kuiper belt object]]s using the observatory's {{convert|1.22|m|in|adj=on|sp=us}} [[Samuel Oschin telescope]] with its wide-field [[CCD camera]], which was operated jointly with the nightly [[Near Earth Asteroid Tracking]] program at Palomar.<ref name="Trujillo2003"/>{{rp|page=100}} This survey was responsible for the discovery of several other large objects beyond [[Neptune]], which includes the [[dwarf planet]]s {{dp|Eris}}, {{dp|Sedna}}, and {{dp|Quaoar}}.<ref name="Schilling2008"/>{{rp|page=214}}

{{mp|2002 MS|4}} was found through manual vetting of potential moving objects identified by the team's automatic image-searching software.<ref name="Trujillo2003"/>{{rp|page=101}} It was among the fainter objects detected, just below the survey's [[limiting magnitude]] with an [[apparent magnitude|observed brightness]] of [[magnitude (astronomy)|magnitude]] 20.9.<ref name="Trujillo2003"/>{{rp|pages=99, 103}} Follow-up observations were conducted two months later with Palomar Observatory's {{convert|1.52|m|in|adj=on|sp=us}} telescope on 8 August 2002.<ref name="MPEC-2002-W27"/> The discovery was announced by the [[Minor Planet Center]] on 21 November 2002 and the object was given the [[minor planet]] [[provisional designation]] of {{mp|2002 MS|4}}.<ref name="MPEC-2002-W27"/>

{{multiple image
| direction         = horizontal
| align             = center
| total_width       = 500
| image1            = P48 1994 Jean Large.jpg
| image2            = 2002 MS4 discovery annotated zoom.gif
| caption1          = The 1.2-meter [[Samuel Oschin telescope]] that was used to discover {{mp|2002 MS|4}} at [[Palomar Observatory]]
| caption2          = Discovery images of {{mp|2002 MS|4}} from 18 June 2002
}}

=== Further observations ===
Since receiving follow-up in August 2002, {{mp|2002 MS|4}} remained unobserved for more than nine months until it was recovered by Trujillo at Palomar Observatory on 29 May 2003, followed by observations by [[Wolf Bickel]] at [[Bergisch Gladbach Observatory]] in Germany in June 2003.<ref name="MPEC-2003-M44"/> These recovery observations significantly improved {{mp|2002 MS|4}}'s orbit, allowing for further extrapolation of its position backwards in time for identification in [[precovery]] observations.<ref name="lowe"/> Seven precovery observations from [[Digitized Sky Survey]] [[photographic plate|plates]] were identified by astronomer Andrew Lowe in 2007; the earliest of these was taken on 8 April 1954 by [[Palomar Observatory]].<ref name="lowe"/><ref name="MPS231732"/>{{rp|page=42}} {{Asof|2023}}, {{mp|2002 MS|4}} [[observation arc|has been observed]] for over 68 years, or about 25% of its [[orbital period]].<ref name="jpldata"/><ref name="MPC-object"/>

=== Numbering and naming ===
{{mp|2002 MS|4}} received its permanent [[Minor-planet designation|minor planet catalog number]] of 307261 from the Minor Planet Center on 10 December 2011.<ref name="lowe"/><ref name="MPC77416"/>{{rp|page=292}} As of yet, it remains unnamed and the discoverers' privilege for naming this object has expired ten years after its numbering.<ref name="MPC-object"/><ref name="wgsbn"/>{{rp|page=6}} Per naming guidelines by the [[International Astronomical Union]]'s [[Working Group for Small Bodies Nomenclature]], {{mp|2002 MS|4}} is open for name suggestions that pertain to creation myths, as required for Kuiper belt objects in general.<ref name="wgsbn"/>{{rp|page=8}}

== Orbit and classification ==
{{mp|2002 MS|4}} is a [[trans-Neptunian object]] (TNO) orbiting the [[Sun]] beyond Neptune with an orbital period of 269 years.<ref name="horizons-ssb"/>{{efn|name=barycentric|These orbital elements are expressed in terms of the [[Solar System Barycenter]] (SSB) as the frame of reference.<ref name="horizons-ssb"/> Due to planetary [[perturbation (astronomy)|perturbations]], the Sun revolves around the SSB at non-negligible distances, so heliocentric-frame orbital elements and distances can vary in short timescales as shown in [[JPL Horizons On-Line Ephemeris System|JPL-Horizons]].<ref name="horizons-heliocentric"/>}} Its [[semi-major axis]] or average orbital distance from the Sun is 41.7 [[astronomical unit]]s (AU), with a moderate<ref name="Gladman2008"/>{{rp|page=45}} [[orbital eccentricity]] of 0.15.<ref name="horizons-ssb"/> In its eccentric orbit, {{mp|2002 MS|4}} comes within 35.7&nbsp;AU from the Sun at [[perihelion]] and 47.8&nbsp;AU at [[aphelion]].<ref name="horizons-ssb"/> It has an [[orbital inclination]] of nearly 18° with respect to the [[ecliptic]].<ref name="horizons-ssb"/> {{mp|2002 MS|4}} last passed perihelion in April 1853, passed aphelion in February 1987, and will make its next perihelion passage in June 2123.<ref name="perihelion-1853"/><ref name="aphelion-1987"/><ref name="perihelion-2123"/>

{{mp|2002 MS|4}} is located in the classical region of the [[Kuiper belt]] 37–48&nbsp;AU from the Sun,<ref name="Lykawka2007"/>{{rp|page=227}} and is thus classified as a [[classical Kuiper belt object]] or cubewano.<ref name="Gladman2008"/>{{rp|page=53}} {{mp|2002 MS|4}}'s high orbital inclination qualifies it as a dynamically "hot" member of the classical Kuiper belt, which implies that it was gravitationally [[perturbation (astronomy)|scattered]] out to its present location by Neptune's outward [[planetary migration]] in the Solar System's early history.<ref name="Lykawka2007"/>{{rp|pages=227, 229}} {{mp|2002 MS|4}}'s present orbit is far enough from Neptune ([[minimum orbit intersection distance]] 6.6&nbsp;AU)<ref name="MPC-object"/> that it no longer experiences scattering from close encounters with the planet.<ref name="Buie"/><ref name="Lykawka2007"/>{{rp|page=214}}

A dynamical study in 2007 simulated {{mp|2002 MS|4}}'s orbital evolution over a 10-million-year timespan and found that it may be in an intermittent 18:11 mean-motion [[orbital resonance]] with Neptune,<ref name="Lykawka2007"/>{{rp|page=218}} which seems to cause irregular fluctations in {{mp|2002 MS|4}}'s orbital inclination and eccentricity.<ref name="Lykawka2007"/>{{rp|page=225}} Despite this, researchers do not consider {{mp|2002 MS|4}} to be in resonance with Neptune.<ref name="Buie"/><ref name="Gladman2008"/>{{rp|page=56}}<ref name="Verbiscer2022"/>{{rp|page=2}}
{{multiple image
| direction         = horizontal
| align             = center
| total_width       = 500
| image1            = 2002 MS4 resonance.gif
| image2            = 2002 MS4 orbit 2018.png
| caption1          = The 18:11-[[Orbital resonance|resonant]] libration of {{mp|2002 MS|4}}'s nominal orbit, in a frame co-rotating with [[Neptune]]
| caption2          = Top and side views of {{mp|2002 MS|4}}'s orbit (white) with [[Pluto]] and other [[classical Kuiper belt object]]s for comparison
}}
{{clear|left}}

== Observability ==
[[File:2002 MS4-sky.png|thumb|upright=1.5|{{mp|2002 MS|4}}'s position in the [[constellation (astronomy)|constellation]] [[Scutum (constellation)|Scutum]] in 2020, moving eastward (left) across the brightest areas of the [[Milky Way]]]]

In the night sky, {{mp|2002 MS|4}} is located near the [[Milky Way]]'s [[Galactic Center]] in the [[southern celestial hemisphere]]. It has been passing through that region's dense field of background stars since its discovery.<ref name="Verbiscer2022"/>{{rp|page=9}} Combined with {{mp|2002 MS|4}}'s faint [[apparent magnitude]] of 20.5 as seen from Earth,<ref name="AstDys"/> its crowded location can make Earth-based observations difficult.<ref name="Thirouin2013"/>{{rp|page=92}}<ref name="Verbiscer2022"/>{{rp|page=9}} On the other hand, {{mp|2002 MS|4}}'s location makes it viable for observing [[stellar occultation]]s as there are numerous stars for it to pass in front of.<ref name="Verbiscer2022"/>{{rp|page=9}}

=== Occultations ===
{| class="wikitable floatright" style="text-align: center; font-size: 0.9em; margin-right: 12px;"
|+ {{mp|2002 MS|4}} occultations observed in 2019–2022<ref name="Rommel2023"/>{{rp|pages=5, 18B.4}}
!Date!!Star apparent<br/>magnitude<br/>([[Photometric system|V-band]])!!Positive<br/>detections!!Negative<br/>detections{{efn|Telescopes that were affected by poor weather or technical problems are not counted as negative detections.}}!!Number of<br/>telescope<br/>locations{{efn|Telescopes that are located in the same place or are located very close together are considered single locations.}}!!Continents<br/>observed
|-
|09 Jul 2019
|15.00
|2
|4
|10
|South America
|-
|26 Jul 2019
|17.78
|3
|0
|3
|South America
|-
|26 Jul 2019
|15.45
|1
|0
|1
|North America
|-
|19 Aug 2019
|16.51
|2
|0
|2
|North America
|-
|26 Jul 2020
|14.76
|2
|0
|5
|Africa
|-
|8 Aug 2020
|14.62
|61
|40
|116
|Europe, Africa, Asia
|-
|24 Feb 2021
|16.51
|1
|1
|2
|South America
|-
|14 Oct 2021
|15.83
|2
|0
|14
|North America
|-
|10 Jun 2022
|15.1
|3
|0
|3
|North America, Africa
|}

Stellar occultations by {{mp|2002 MS|4}} occur when it passes in front of a star and blocks out its light, causing the star to dim for several seconds until {{mp|2002 MS|4}} emerges.<ref name="Rommel2023"/>{{rp|page=2}} Observing stellar occultations by {{mp|2002 MS|4}} can provide precise measurements for its position, shape, and size.<ref name="Rommel2023"/>{{rp|page=1}}<ref name="Peng2023"/>{{rp|page=35}} Due to [[parallax]] between Earth, {{mp|2002 MS|4}}, and the occulted star, occultations by {{mp|2002 MS|4}} may only be observable to certain locations on Earth. For this reason, the {{mp|2002 MS|4}}'s orbital trajectory and [[ephemeris]] must be precisely known before occultation predictions can be reliably made.<ref name="Rommel2023"/>{{rp|page=2}}<ref name="Peng2023"/>{{rp|page=35}}

To facilitate occultation predictions for {{mp|2002 MS|4}}, astronomers of the [[European Research Council]]'s ''Lucky Star'' project gathered [[astrometry|astrometric]] observations of {{mp|2002 MS|4}} from 2009–2019 to reduce its orbital uncertainty and utilized the [[Gaia catalogues|''Gaia'' catalogues]] for high-precision positions of stars.<ref name="Rommel2020"/><ref name="Rommel2023"/>{{rp|page=2}} From 2019–2022, the ''Lucky Star'' project organized campaigns for astronomers worldwide to observe the predicted occultations by {{mp|2002 MS|4}}, yielding nine successfully-observed occultations by the end of the period.<ref name="Rommel2023"/>{{rp|pages=1, 3}} The first successfully-observed occultation by {{mp|2002 MS|4}} took place in South America on 9 July 2019, which yielded two positive detections and four negative detections from the 10 participating telescope locations; the remaining four telescopes were affected by poor weather.<ref name="Rommel2020"/><ref name="Rommel2023"/>{{rp|pages=2, 18B.4}} More successful observations of {{mp|2002 MS|4}}'s occultations took place on 26 July and 19 August 2019, which provided highly precise astrometry that helped refine later occultation predictions.<ref name="LuckyStar-20200808"/><ref name="Rommel2023"/>{{rp|page=2}}

On 8 August 2020, the ''Lucky Star'' project organized a large observing campaign for {{mp|2002 MS|4}}, which would occult a relatively bright star of apparent magnitude 14.6 and be observable over densely-populated regions in multiple continents.<ref name="Rommel2023"/>{{rp|page=4}} A total of 116 telescope locations from Europe, North Africa, and Western Asia participated in the campaign and yielded 61 positive detections and 40 negative detections, with the remaining 15 telescopes inhibited by poor weather or technical difficulties.<ref name="Rommel2023"/>{{rp|pages=4, 18B.1–3}} The observers of the occultation found no evidence of [[Ring system|rings]], [[Comet#Jet|cometary jets]], or [[natural satellite]]s around {{mp|2002 MS|4}}.<ref name="Rommel2023"/>{{rp|page=9}} This is the most extensive participation in a TNO occultation campaign {{asof|2023|lc=y}}.<ref name="Kilic2022"/>{{rp|page=1347}}<ref name="Rommel2023"/>{{rp|page=9}} Thanks to the large amount of positive detections across various locations, the global shape outline and [[topography]] of {{mp|2002 MS|4}} could be seen clearly for the first time.<ref name="Rommel2021"/><ref name="Rommel2023"/>

<gallery mode="packed" heights="200px">
File:2002 MS4 occultation map - Rommel et al. 2023 Fig 3.tif|Map showing the location of telescopes that participated in the 8 August 2020 occultation campaign. Telescopes within the path of {{mp|2002 MS|4}}'s shadow (region between the two solid blue curves) made positive detections (blue and red points), whereas telescopes outside the path made negative detections (green points).
File:2002 MS4 occultation chords - Rommel et al. 2023 Fig 1.tif|{{mp|2002 MS|4}}'s projected shape revealed by the many positive detection [[chord (astronomy)|chords]] from the 8 August 2020 occultation (blue with red error bars). A massive topographic peak and depression is visible along {{mp|2002 MS|4}}'s [[lunar limb|limb]] in the northeast direction.
</gallery>

== Physical characteristics ==
{| class="wikitable floatleft" style="text-align: center; font-size: 0.9em; margin-right: 12px;"
|+ History of diameter estimates for {{mp|2002 MS|4}}
!Year of<br/>Publication!!Diameter<br/>(km)!!Method!!Refs
|-
|2008
|{{val|726.2|123.2|122.9}}
|thermal<br/>{{small|(''Spitzer'')}}
|<ref name="Stansberry2008"/>{{rp|page=173}}
|-
|2009
|{{val|730|118|120}}
|thermal<br/>{{small|(''Spitzer'', remodeled)}}
|<ref name="Brucker2009"/>{{rp|page=291}}
|-
|2012
|{{val|934|47}}
|thermal<br/>{{small|(''Herschel'')}}
|<ref name="Vilenius2012"/>{{rp|page=10}}
|-
|2020
|{{val|770|2}}
|occultation<br/>{{small|(9 Jul 2019)}}
|<ref name="Rommel2020"/>
|-
|2022
|{{val|810|70|p=<}}
|occultation<br/>{{small|(26 Jul 2019)}}
|<ref name="Zemouri2022"/>
|-
|2023
|'''{{val|796|24}}'''
|occultation<br/>{{small|(8 Aug 2020)}}
|<ref name="Rommel2023"/>{{efn|Rommel et al. previously reported a diameter of {{val|800|24|u=km}} in a 2021 conference talk about their preliminary 8 August 2020 occultation results.<ref name="Rommel2021"/> This preliminary diameter estimate has been superseded by the more recent estimate of {{val|796|24|u=km}} in their paper published in 2023.<ref name="Rommel2023"/>}}
|}

Results from the extensively observed 8 August 2020 occultation show that {{mp|2002 MS|4}} has a shape close to that of an [[oblate spheroid]], with an equatorial diameter of {{cvt|814|km|mi}} and a polar diameter of up to {{cvt|770|km|mi}}.<ref name="Rommel2023"/>{{rp|page=5}} {{mp|2002 MS|4}}'s mean diameter from these dimensions is {{cvt|796|km|mi}}, which places it between the diameters of the two largest asteroids, [[Ceres (dwarf planet)|Ceres]] and [[4 Vesta|Vesta]].<ref name="Rommel2023"/>{{rp|page=5}} It is unknown whether {{mp|2002 MS|4}}'s equator is being viewed obliquely or edge-on from Earth's perspective, so it is possible that the object's actual polar diameter may be smaller, or have a greater [[oblateness]], than observed in the August 2020 occultation.<ref name="Rommel2023"/>{{rp|page=8}} {{mp|2002 MS|4}} is the 10th (or 11th if counting Pluto's moon [[Charon (moon)|Charon]]) largest known TNO. Because of its large size, it is considered a [[List of possible dwarf planets|dwarf planet candidate]] by astronomers.<ref name="Pinilla-Alonso2015"/>{{rp|page=245}}<ref name="Rommel2023"/>{{rp|page=1}}<ref name="Peng2023"/>{{rp|page=iii}} With measurement uncertainties considered, it is approximately tied with {{mpl|2002 AW|197}} and {{mpl|2013 FY|27}} (diameters {{val|729|-|807|u=km}}<ref name="Vilenius2014"/> and {{val|659|-|820|u=km}},<ref name="Sheppard2018"/> respectively) as the [[List of Solar System objects by size|largest unnamed object in the Solar System]].

{{mp|2002 MS|4}} was previously thought to have a larger diameter of {{cvt|934|km|mi}}, according to [[infrared]] [[thermal radiation|thermal emission]] measurements made by the ''[[Spitzer Space Telescope|Spitzer]]'' and ''[[Herschel Space Observatory|Herschel]]'' space telescopes in 2006 and 2010.<ref name="Vilenius2012"/>{{rp|pages=4, 7, 10}} This thermal emission-derived diameter disagrees with the occultation-derived diameter; if both the thermal emission measurements and occultation-derived diameter are correct, then {{mp|2002 MS|4}} would be emitting more thermal radiation than predicted if it were a non-rotating, simple airless body.<ref name="Peng2023"/>{{rp|page=68, 70, 73}} It is not yet clear why {{mp|2002 MS|4}} seems to be emitting excess thermal radiation; it could be possible that either there is an unknown satellite of {{mp|2002 MS|4}} contributing to the excess thermal emission,<ref name="Rommel2023"/>{{rp|page=9}} or the predictions for {{mp|2002 MS|4}}'s thermal emission behavior are inaccurate.<ref name="Peng2023"/>{{rp|page=73}}

The mass and density of {{mp|2002 MS|4}} is unknown since it has no known moons, which would have made mass estimates possible by [[Kepler's third law]].<ref name="Peng2023"/>{{rp|page=35}} Without a known mass and density, it is not possible to determine whether {{mp|2002 MS|4}}'s spheroidal shape is due to [[hydrostatic equilibrium]], which would qualify it as a [[dwarf planet]].<ref name="Lineweaver2009"/>{{rp|page=10}} Inferring from its diameter and albedo, {{mp|2002 MS|4}} is probably not in hydrostatic equilibrium since it lies within the {{cvt|400-1000|km|mi}} diameter range where TNOs are typically observed with very low densities, presumably due to having highly [[porosity|porous]] interior structures that have not gravitationally compressed into solid bodies.<ref name="Grundy2019"/>{{rp|pages=1, 8}} Otherwise, if {{mp|2002 MS|4}} is in hydrostatic equilibrium, then its density could be estimated from its oblateness and rotation period.<ref name="Rommel2023"/>{{rp|page=8}} However, both of these properties are poorly known for {{mp|2002 MS|4}}, so only its minimum and maximum possible densities could be estimated.<ref name="Rommel2023"/>{{rp|page=8}} Assuming a [[Maclaurin spheroid]] as the equilibrium shape for {{mp|2002 MS|4}}, the ranges of possible densities are {{val|0.72|-|8.0|u=g/cm3}} and {{val|0.36|-|3.9|u=g/cm3}} for possible rotation periods of 7.44 and 10.44&nbsp;hours, respectively.<ref name="Rommel2023"/>{{rp|page=8}}

=== Surface ===
{{TNO imagemap}}
{{mp|2002 MS|4}} has a gray or spectrally neutral surface color, meaning it reflects similar amounts of light for [[wavelength]]s across the [[visible spectrum]].<ref name="Tegler2016"/>{{rp|page=6}} In Barucci et al.'s classification scheme for [[Trans-Neptunian object#Color indices|TNO color indices]], {{mp|2002 MS|4}} falls under the BB group of TNOs with neutral colors, whose surface compositions characteristically have a high fraction of water ice and [[amorphous carbon]] but low amounts of [[tholin]]s.<ref name="Barucci2005"/>{{rp|page=1294, 1296}} [[Near-infrared]] [[spectroscopy]] by the [[James Webb Space Telescope]] (JWST) in 2022 revealed the presence of [[Ice|crystalline water ice]], [[Amorphous ice|amorphous water ice]], and [[carbon dioxide]] ice in {{mp|2002 MS|4}}'s surface.<ref name="Cook2023"/><ref name="Cook2023-eposter"/> The large Kuiper belt object [[120347 Salacia]] was observed by JWST to have a similar surface composition as {{mp|2002 MS|4}}.<ref name="Cook2023-eposter"/> Preliminary modeling of {{mp|2002 MS|4}}'s JWST spectrum by Cook et al. suggests that the water ice on the object's surface consists of micrometer-sized grains and the carbon dioxide ice consists of a mix of coarser, micrometer-sized grains to finer, sub-micrometer-sized grains.<ref name="Cook2023-eposter"/> Tholins should also exist on {{mp|2002 MS|4}}'s surface according to Cook et al.'s preliminary model, although they have not been detected in {{mp|2002 MS|4}}'s JWST spectrum.<ref name="Cook2023-eposter"/> [[Volatile (astrogeology)|Volatile]] ices such as [[methane]] were also not detected in {{mp|2002 MS|4}}'s JWST spectrum.<ref name="Cook2023"/> The lack of volatiles on {{mp|2002 MS|4}}'s surface agrees with its low [[geometric albedo]] of 0.1 determined from observations by the ''[[New Horizons (spacecraft)|New Horizons]]'' spacecraft, which indicates {{mp|2002 MS|4}} has a very dark and unevolved surface in contrast to the bright and volatile-rich dwarf planets like Pluto.<ref name="Verbiscer2022"/>{{rp|pages=2, 18–19}} ''New Horizons'' observations of {{mp|2002 MS|4}}'s [[Phase curve (astronomy)|phase curve]] indicate that the icy [[regolith]] grains on the object's surface are rough and irregularly shaped.<ref name="Verbiscer2022"/>{{rp|page=19}}

=== Topographic features ===
{{multiple image
| direction         = vertical
| align             = right
| total_width       = 300
| image1            = 2002 MS4 shape - Rommel et al. 2023 Fig 6.tif
| image2            = 2002 MS4 limb topography - Rommel et al. 2023 Fig 5.tif
| caption1          = Projected shape of {{mp|2002 MS|4}} seen in the 8 August 2020 occultation
| caption2          = Plot of topographic elevation variations along {{mp|2002 MS|4}}'s limb
}}

The 8 August 2020 occultation revealed massive topographic features along {{mp|2002 MS|4}}'s northeastern outline, or [[lunar limb|limb]], which notably includes a crater-like depression {{cvt|322 ± 39|km|mi}} wide and {{cvt|45.1 ± 1.5|km|mi}} deep, and a {{val|25|4|5|u=km}} ({{val|15.5|2.5|3.1|u=mi}})-tall peak near the rim of the depression.<ref name="Rommel2023"/>{{rp|page=7}} Another depression feature about {{cvt|10|km|mi}} wide and {{cvt|11|km|mi}} deep was detected by a single telescope from [[Varages|Varages, France]] during the occultation; this depression feature partially occulted the star as {{mp|2002 MS|4}} emerged, which resulted in the star brightening gradually instead of instantly.<ref name="Rommel2023"/>{{rp|page=7}} The [[elevation]]s of these observed topographic features lie beyond the maximum elevation of {{cvt|6–7|km|mi}} expected for an icy body of {{mp|2002 MS|4}}'s size, signifying that the object may have experienced a large impact in its past.<ref name="Rommel2023"/>{{rp|pages=6, 9}} It would be possible for {{mp|2002 MS|4}} to support its massive topographic features if its [[Strength of materials|material strength]] increases toward its core.<ref name="Rommel2023"/>{{rp|page=6}} Topographic features on other TNOs have been previously observed through occultation, such as {{mpl|(208996) 2003 AZ|84}} which has a depression feature at least {{cvt|8|km|mi|0}} deep.<ref name="Dias-Oliveira2017"/><ref name="SN-20230829"/>

The topographic peak on {{mp|2002 MS|4}} has a height comparable to [[Mars]]'s tallest mountain, [[Olympus Mons]], and the central mound of the [[Rheasilvia]] crater on asteroid Vesta.<ref name="SN-20230829"/><ref name="Schenk2012"/> If {{mp|2002 MS|4}}'s topographic peak is a mountain, then it would qualify as one of the [[List of tallest mountains in the Solar System|tallest known mountains in the Solar System]].<ref name="SN-20230829"/> It is possible that this topographic peak may actually be an unknown {{cvt|213|km|mi}}-diameter satellite that was [[Planetary transits and occultations|passing in front or behind]] {{mp|2002 MS|4}} during the occultation, but this scenario is unlikely according to Bruno Sicardy, one of the occultation team members.<ref name="Rommel2023"/>{{rp|pages=9, 25}}<ref name="SN-20230829"/> A satellite of this size would not be large enough to explain {{mp|2002 MS|4}}'s excess thermal emission.<ref name="Rommel2023"/>{{rp|pages=25}}

If {{mp|2002 MS|4}}'s massive depression is a crater, then it would be the first observation of a massive crater on a TNO.<ref name="Rommel2023"/>{{rp|page=9}} The depression's width takes up about 40% of {{mp|2002 MS|4}}'s diameter, which is comparable to the largest crater-to-diameter ratios seen in Saturn's moons [[Tethys (moon)|Tethys]] and [[Iapetus (moon)|Iapetus]]. For context, Tethys's largest crater [[Odysseus (crater)|Odysseus]] takes up about 43% of its diameter, while Iapetus's largest crater [[Turgis (crater)|Turgis]] takes up about 40% of its diameter.<ref name="Rommel2023"/>{{rp|page=9}} The trans-Neptunian dwarf planets Pluto and Charon do not exhibit such large craters on the other hand,{{efn|Pluto has an over-{{cvt|1000|km|mi}}-wide ice-covered basin named [[Sputnik Planitia]], although it is unclear whether it originated from an impact.}} as their largest crater-to-diameter ratios are 10.5% and 18.9%, respectively.<ref name="Rommel2023"/>{{rp|page=9}} The depth of {{mp|2002 MS|4}}'s massive depression takes up 5.7% of {{mp|2002 MS|4}}'s diameter and exceeds those seen in the largest craters of other Solar System bodies of comparable size: the largest crater of Saturn's moon [[Mimas (moon)|Mimas]] has a depth of up to {{cvt|10–12|km|mi}}<ref name="Moore2004"/>{{rp|page=424}} and Vesta's Rheasilvia crater has a depth of up to {{cvt|25|km|mi}}.<ref name="Schenk2012"/>

=== Rotation and light curve ===
The [[rotation period]] of {{mp|2002 MS|4}} is uncertain and its rotational [[axial tilt]] is unknown. It is difficult to measure {{mp|2002 MS|4}}'s rotation period [[Photometry (astronomy)|photometrically]] with telescopes on Earth since the object is obscured in a dense field of background stars.<ref name="Thirouin2013"/>{{rp|page=118}}<ref name="Rommel2023"/>{{rp|page=7}} Due to {{mp|2002 MS|4}}'s spheroidal shape and possible surface albedo variations, its [[light curve]] only exhibits very small fluctuations in brightness (amplitude 0.05–0.12 [[magnitude (astronomy)|mag]]<ref name="Peng2023"/>{{rp|page=85}}) over time as it rotates.<ref name="Rommel2023"/>{{rp|page=7}}<ref name="Peng2023"/>{{rp|page=73}} The first attempts at measuring {{mp|2002 MS|4}}'s rotation were made with the [[Sierra Nevada Observatory]]'s 1.5-meter telescope in August 2005, but it did not observe the object long enough to identify any periodicities in its light curve.<ref name="Thirouin2013"/>{{rp|page=31, 92}} Subsequent observations by the [[Galileo National Telescope]] in June–July 2011 took advantage of {{mp|2002 MS|4}} passing in front of a [[dark nebula]], which enabled it to determine possible periods of either 7.33 hours or 10.44 hours, for an assumed single-peaked light curve due to a spheroidal body with albedo variations.<ref name="Thirouin2013"/>{{rp|pages=77, 94}} On the other hand, observations by the [[Canada–France–Hawaii Telescope]] in July–August 2013 measured a rotation period of 14.251 hours, with other less probable rotation period [[aliasing#Sampling sinusoidal functions|aliases]] of 8.932 and 5.881 hours.<ref name="Peng2023"/>{{rp|pages=43, 53, 74}}

== Exploration ==
=== ''New Horizons'' ===
The ''[[New Horizons (spacecraft)|New Horizons]]'' spacecraft observed {{mp|2002 MS|4}} during 2016–2019, as part of its extended Kuiper belt mission after its successful Pluto flyby in 2015.<ref name="Verbiscer2022"/>{{rp|page=8}} {{mp|2002 MS|4}} was {{convert|15.3|AU|e9km e9mi|abbr=unit}} away from the spacecraft when it began observations on 13 July 2016, and was {{convert|12.0|AU|e9km e9mi|abbr=unit}} away from the spacecraft when it ended observations in 1 September 2019.<ref name="Verbiscer2022"/>{{rp|page=8}} ''New Horizons'' had the unique vantage point of observing {{mp|2002 MS|4}} and other TNOs while it was inside the Kuiper belt, which allowed the spacecraft to observe these objects at high [[phase angle (astronomy)|phase angle]]s (>2°) that are not observable from Earth.<ref name="Verbiscer2022"/>{{rp|page=1}} By observing how {{mp|2002 MS|4}}'s brightness changes as a function of phase angle, the object's phase curve could be determined, which can reveal the light [[scattering]] properties of {{mp|2002 MS|4}}'s surface regolith.<ref name="Verbiscer2022"/>{{rp|page=1}} In addition to significantly improving the knowledge of {{mp|2002 MS|4}}'s phase curve, the observations by ''New Horizons'' also significantly improved the precision of {{mp|2002 MS|4}}'s orbit.<ref name="Lakdawalla2018"/>

<gallery mode="packed" heights="200px">
File:2002 MS4 New Horizons.gif|{{mp|2002 MS|4}} imaged by the ''[[New Horizons (spacecraft)|New Horizons]]'' spacecraft in July 2016, from a distance of {{convert|15.3|AU|e9km e9mi|abbr=unit|sigfig=2}}
File:New Horizons KEM Trajectory.png|''New Horizons'' trajectory through the Kuiper belt, with positions of nearby KBOs including {{mp|2002 MS|4}} labeled
</gallery>

=== Proposed ===
{{mp|2002 MS|4}} has been considered as a possible exploration target for future missions to the Kuiper belt and beyond, such as NASA's ''[[Interstellar Probe (spacecraft)|Interstellar Probe]]'' concept.<ref name="Runyon2020"/> A 2019 study by Amanda Zangari and collaborators identified several possible trajectories to {{mp|2002 MS|4}} for a spacecraft that would be launched in 2025–2040.<ref name="Zangari2019"/> For a spacecraft launched in 2027–2031, a single [[gravity assist]] from Jupiter could bring a spacecraft to {{mp|2002 MS|4}} over a minimum duration of 9.1–12.8 years, depending on the [[characteristic energy|excess launch energy]] of the spacecraft.<ref name="Zangari2019"/>{{rp|page=922}} Another trajectory using a single Jupiter gravity assist for a 2040 launch date could bring a spacecraft to {{mp|2002 MS|4}} over a minimum duration of 13 years.<ref name="Zangari2019"/>{{rp|page=922}} A 2038–2040 launch trajectory using a single Saturn gravity assist could bring a spacecraft to {{mp|2002 MS|4}} over a minimum duration of 16.7 years,<ref name="Zangari2019"/>{{rp|page=925}} while a 2038–2040 launch trajectory using two gravity assists from Jupiter and Saturn could bring a spacecraft to {{mp|2002 MS|4}} over a minimum duration of 18.6–19.5 years.<ref name="Zangari2019"/>{{rp|page=923}}

== See also ==
* [[List of Solar System objects by size]]

== Notes ==
{{notelist}}
== References ==
{{reflist|30em|refs=

<ref name="jpldata">{{cite web
  |type       = 2022-07-04 last obs.
  |title      = JPL Small-Body Database Lookup: 307261 (2002 MS4)
  |url        = https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=2307261
  |publisher  = [[Jet Propulsion Laboratory]]
  |accessdate = 10 December 2023}}</ref>

<ref name="horizons-ssb">{{cite web
  |title      = JPL Horizons On-Line Ephemeris for 307261 (2002 MS4) at epoch JD 2460000.5
  |url        = https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND='307261'&TABLE_TYPE='ELEMENTS'&START_TIME='JD2460000.5'&STOP_TIME='JD2460200.5'&STEP_SIZE='1y'&CENTER='@0'&OUT_UNITS='AU-D'
  |work       = [[JPL Horizons On-Line Ephemeris System]]
  |publisher  = Jet Propulsion Laboratory
  |accessdate = 19 June 2022}} Solution using the Solar System [[Barycenter]]. Ephemeris Type: Elements and Center: @0)</ref>

<ref name="horizons-heliocentric">{{cite web
  |title      = JPL Horizons On-Line Ephemeris for 307261 (2002 MS4) at epochs JD 2450000.5–2460000.5
  |url        = https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND='307261'&TABLE_TYPE='ELEMENTS'&START_TIME='JD2450000.5'&STOP_TIME='JD2470000.5'&STEP_SIZE='200d'&CENTER='500@10'&OUT_UNITS='AU-D'
  |work       = [[JPL Horizons On-Line Ephemeris System]]
  |publisher  = Jet Propulsion Laboratory
  |accessdate = 28 June 2022}} Solution using the Sun. Ephemeris Type: Elements and Center: @sun)</ref>

<ref name="perihelion-1853">{{cite web
  |title      = JPL Horizons On-Line Ephemeris for 307261 (2002 MS4) from 1853-Jan-01 to 1854-Jan-01
  |url        = https://ssd.jpl.nasa.gov/api/horizons.api?format=text&COMMAND='307261'&OBJ_DATA='YES'&MAKE_EPHEM='YES'&EPHEM_TYPE='OBSERVER'&CENTER='@sun'&START_TIME='1853-01-01'&STOP_TIME='1854-01-01'&STEP_SIZE='1d'&QUANTITIES='20'
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<ref name="aphelion-1987">{{cite web
  |title      = JPL Horizons On-Line Ephemeris for 307261 (2002 MS4) from 1987-Jan-01 to 1988-Jan-01
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<ref name="perihelion-2123">{{cite web
  |title      = JPL Horizons On-Line Ephemeris for 307261 (2002 MS4) from 2123-Jan-01 to 2124-Jan-01
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<ref name="lowe">{{cite web
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}} <!-- end of refs -->

== External links ==
* [http://andrew-lowe.ca/2002ms4.htm {{mp|(307261) 2002 MS|4}} Precovery Images], Andrew Lowe
* {{JPL small body|id=307261}}

{{Minor planets navigator| |number=307261 |PageName={{mp|(307261) 2002 MS|4}} |}}
{{Dwarf planets}}
{{Small Solar System bodies}}
{{Trans-Neptunian objects}}
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{{DEFAULTSORT:2002 MS4}}
[[Category:Classical Kuiper belt objects|307261]]
[[Category:Discoveries by Michael E. Brown]]
[[Category:Discoveries by Chad Trujillo]]
[[Category:Possible dwarf planets|307261]]
[[Category:Objects observed by stellar occultation]]
[[Category:Astronomical objects discovered in 2002|20020618]]
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