(307261) 2002 MS₄

(307261) 2002 MS₄ is a large classical Kuiper belt object and a possible dwarf planet in the Kuiper belt, a region of icy planetesimals beyond Neptune.^[13] It was discovered in 2002 by Chad Trujillo and Michael Brown, and has precovery images back to 8 April 1954.^[2]

(307261) 2002 MS₄

2002 MS4 imaged by the Hubble Space Telescope on 9 April 2006
Discovery^[1]
Discovered by	Chadwick A. Trujillo Michael E. Brown
Discovery site	Palomar Obs.
Discovery date	18 June 2002
Designations
MPC designation	2002 MS4
Minor planet category	TNO^[2] · cubewano (hot)^[3]^: 56 distant^[1] · Scat-Ext^[4]
Orbital characteristics (barycentric)^[6]^[2]
Epoch 25 February 2023 (JD 2460000.5)
Uncertainty parameter 3
Observation arc	66.22 yr (24,188 days)
Earliest precovery date	8 April 1954
Aphelion	47.801 AU
Perihelion	35.677 AU
Semi-major axis	41.739 AU
Eccentricity	0.14524
Orbital period (sidereal)	269.48 yr (98,429 d)
Mean anomaly	226.844°
Mean motion	0° 0^m 13.167^s / day
Inclination	17.693°
Longitude of ascending node	216.075°
Time of perihelion	≈ 12 June 2123^[5] ±5 days^[2]
Argument of perihelion	214.575°
Physical characteristics
Dimensions	808±11 × 748±15 km RMS (projected)^[7]^[8]
Mean diameter	800±24 km^[8]
Synodic rotation period	7.33 h or 10.44 h (single-peaked)^[9]
Geometric albedo	0.098±0.004 (geometric)^[10]^: 2 0.039±0.005 (Bond)^[10]^: 23
Spectral type	B−V=0.69±0.02^[11]^: 6 V−R=0.38±0.02 B−R=1.07±0.02
Apparent magnitude	20.5^[12]
Absolute magnitude (H)	4.0±0.6^[13]^: 7 3.62^[2]^[1]

As of 2021^[update], 2002 MS₄ is 46.4 AU from the Sun.^[12] It will reach perihelion, its closest point to the Sun, in 2123.^[5] At 800 km (500 mi) in diameter, it is approximately tied with 2002 AW197 and 2013 FY27 (to within measurement uncertainties) as the largest unnamed object in the Solar System.

History

Discovery

2002 MS₄ was discovered on 18 June 2002 by astronomers Chad Trujillo and Michael Brown at Palomar Observatory in San Diego County, California, United States.^[1] The discovery formed part their Caltech Wide Area Sky Survey for bright Kuiper belt objects using the observatory's 1.22-meter (48 in) Samuel Oschin telescope with its wide-field CCD camera, which was operated jointly with the nightly Near Earth Asteroid Tracking program at Palomar.^[14]: 100 This survey was responsible for the discovery of several other large, distant objects, including the dwarf planets Eris, Sedna, and Quaoar.^[15]: 214

2002 MS₄ was found through manual vetting of potential moving objects identified by the team's automatic image-searching software.^[14]: 101 It was among the fainter objects detected, just below the survey's limiting magnitude with an observed brightness of magnitude 20.9.^{[14]: 99, 103} Follow-up observations were conducted two months later with Palomar Observatory's 1.52-meter (60 in) telescope on 8 August 2002.^[16] The discovery was announced by the Minor Planet Center on 21 November 2002 and the object was given the minor planet provisional designation of 2002 MS₄.^[16]

 

The 1.2-meter Samuel Oschin telescope that was used to discover 2002 MS₄ at Palomar Observatory

 

Discovery images of 2002 MS₄ from 18 June 2002

Further observations

Since receiving follow-up in August 2002, 2002 MS₄ 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.^[17] These recovery observations significantly improved 2002 MS₄'s orbit, allowing for further extrapolation of its position backwards in time for identification in precovery observations.^[18] Seven precovery observations from Digitized Sky Survey plates were identified by astronomer Andrew Lowe in 2007; the earliest of these was taken on 8 April 1954 by Siding Spring Observatory in New South Wales, Australia.^{[18][19]: 42}

As of 2022^[update], 2002 MS₄ has a well-determined orbit with an uncertainty parameter of 3.^[2] With an observation arc of over 66 years, it has been observed throughout 24% of its orbital period.^[2][1]

Numbering and naming

2002 MS₄ received its permanent minor planet number of 307261 by the Minor Planet Center on 10 December 2011.^{[18][20]: 292} As of yet, it remains unnamed and the discoverers' privilege for naming this object has expired ten years since its numbering.^[1][21]: 6 Per naming guidelines by the International Astronomical Union's Working Group Small Body Nomenclature, 2002 MS₄ is open for name suggestions that pertain to creation myths, as required for Kuiper belt objects in general.^[21]: 8

Visibility

 

2002 MS₄'s position in the constellation Scutum, moving eastward across the brightest areas of the Milky Way

2002 MS₄ is located near the Milky Way's Galactic Center in the southern celestial hemisphere and it has been passing through that region's dense field of background stars since its discovery.^[10]: 9 Combined with its faint apparent magnitude of 20.5 as seen from Earth,^[12] 2002 MS₄ at its crowded location can make Earth-based observations difficult.^{[9]: 92 [10]: 9} On the other hand, 2002 MS₄'s location also makes it viable for observing stellar occultations as there are numerous stars for it to pass in front of.^[10]: 9 Several occultation events by 2002 MS₄ have been observed from Earth since 2019,^[22][23] including one noteworthy event that involved an international campaign of 116 observers on 8 August 2020.^[8]

Orbit and classification

 

The 18:11-resonant libration of 2002 MS₄'s nominal orbit, in a frame co-rotating with Neptune

 

Top and side views of 2002 MS₄'s orbit (white) with Pluto and other classical Kuiper belt objects for comparison

2002 MS₄ orbits beyond Neptune with an orbital period of 269 years.^[6][a] Its semi-major axis or average orbital distance from the Sun is 41.7 astronomical units (AU), with a moderate^[3]: 45 orbital eccentricity of 0.15.^[6] In its eccentric orbit, 2002 MS₄ comes within 35.7 AU from the Sun at perihelion and 47.8 AU at aphelion.^[6] It has an orbital inclination of nearly 18° with respect to the ecliptic.^[6] 2002 MS₄ last passed perihelion in April 1853 and will make its next perihelion passage in June 2123.^[25][5]

2002 MS₄ is located in the classical region of the Kuiper belt 37–48 AU from the Sun,^[26]: 227 and is thus classified as a classical Kuiper belt object or cubewano.^[3]: 53 Its high orbital inclination qualifies it as a dynamically "hot" member of the classical Kuiper belt, which implies it may have been gravitationally scattered out to its present location by Neptune early in its history.^{[26]: 227, 229} 2002 MS₄'s present orbit is far enough from Neptune (minimum orbit intersection distance 6.6 AU)^[1] that it no longer experiences scattering from close encounters with the planet.^{[4][26]: 214}

2002 MS₄ is in an intermittent 18:11 mean-motion orbital resonance with Neptune, as shown in numerical simulations of its orbit over a 10-million-year timespan.^[26]: 218 This weak resonance primarily affects 2002 MS₄'s orbital inclination irregularly, but it may alternate to affecting its eccentricity as well.^[26]: 225

Physical characteristics

Size

Size estimates for 2002 MS₄

Year of Publication	Diameter (km)	Method	Refs
2008	726.2+123.2 −122.9	thermal (Spitzer)	^[27]^: 173
2009	730+118 −120	thermal (Spitzer, remodeled)	^[28]^: 291
2012	934±47	thermal (Herschel)	^[13]^: 10
2020	770±2	occultation (9 Jul 2019)	^[22]
2021	800±24	occultation (8 Aug 2020)	^[8]

 

Artistic comparison of Pluto, Eris, Haumea, Makemake, Gonggong, Quaoar, Sedna, Orcus, Salacia, 2002 MS₄, and Earth along with the Moon

• v
• t
• e

In 2008, the Spitzer Space Telescope estimated it to have a diameter of 726±123 km and the Herschel Space Telescope estimated it to be 934±47 km.^[27]: 173

Seven occultation events were observed from 2019 to 2021. The most successful was on 8 August 2020, involving 116 telescopes. The result was a diameter of 800±24 km; the ±24-km variation is thought to be largely due to surface features.^[8]

2002 MS₄ has measured color indices of B−V=0.69±0.02 and V−R=0.38±0.02, which indicates that it has a neutral (gray) surface color.^[11]: 6 In Barucci et al.'s classification scheme for TNO color indices, 2002 MS₄ falls under the BB group of TNOs with neutral colors.^[29]: 1294 No reflectance spectrum of 2002 MS₄ has been measured as of yet, thus its surface composition remains unknown.^[10]: 10 Nevertheless, it can be inferred that 2002 MS₄ lacks volatiles such as nitrogen and methane due to its low geometric albedo of 0.1 determined from New Horizons observations.^{[10]: 2, 18–19} This low albedo indicates that 2002 MS₄ has a very dark and unevolved surface depleted in volatiles.^{[10]: 18–19}

Occultations

 

2002 MS₄'s projected shape as seen from positive detections of the 8 August 2020 occultation (blue). A topographic peak and depression is visible along 2002 MS₄'s limb in the northeast direction.^[8]

Two stellar occultations by 2002 MS₄ were observed from South America and Canada on 9 July and 26 July 2019, both yielding at least two positive detections from participating observers. A negative chord grazing the projected shape of 2002 MS₄ on the 9 July event allowed for constraints on its diameter, yielding a best-fit equivalent spherical radius of 770±2 km.^[22] In the following month, two observers from Canada recorded another stellar occultation by 2002 MS₄ on 19 August 2019. The two positive chords from the event suggested that 2002 MS₄ may have an oblate shape, with projected dimensions of 842 × 688 km.^[30]

On 8 August 2020, a campaign organized by Lucky Star project successfully observed the occultation of a magnitude 14.6 star with 61 positive detections.^[31][8] The resulting projected dimensions of 2002 MS₄ were 808 × 748 km, consistent with the results from the previous year.^[7] Topographic features 20 km (12 mi) in depth and height were observed on 2002 MS₄'s surface.^[8]

Rotation

As of 2019^[update], the rotation period of 2002 MS₄ is unknown. Observations in 2005 and 2011 showed possible periods of either 7.33 hours or its alias 10.44 hours (single-peaked), or twice those values for the double-peaked solution, with a small light curve amplitude of 0.05±0.01 mag. Light curve observations of 2002 MS₄ are difficult because of the dense field of background stars it is crossing. Observations made in June and July 2011 took advantage of 2002 MS₄ moving in front of a dark nebula.^[9]: 118

No known moons; possible dwarf status

2002 MS₄ does not have any known moons orbiting it; thus an accurate mass estimate cannot be made. Based on its size alone, Brown lists it as nearly certain to be a dwarf planet.^[32] However, its low albedo may imply the opposite: dark, mid-sized bodies such as this, less than about 900–1000 km in diameter and with albedos less than about 0.2 that suggest they have never been resurfaced, have likely never collapsed into solid bodies, much less differentiated or relaxed into hydrostatic equilibrium, and thus are unlikely to be dwarf planets.^[33]: 16

Exploration

New Horizons

 

2002 MS₄ imaged by the New Horizons spacecraft in July 2016, from a distance of 15.3 AU (2.3 billion km; 1.4 billion mi)

 

New Horizons trajectory through the Kuiper belt, with positions of nearby KBOs including 2002 MS₄ labeled

From July 2016 to September 2019, 2002 MS₄ was observed by the New Horizons spacecraft, as part of its extended Kuiper belt mission.^[10]: 11 The observations significantly improved the knowledge of 2002 MS₄'s orbit and phase curve behavior from the scattering properties of its surface.^[34][35]

See also

• List of Solar System objects by size

Notes

1. These orbital elements are expressed in terms of the Solar System Barycenter (SSB) as the frame of reference.^[6] Due to planetary 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.^[24]

References

1. "(307261) = 2002 MS4". Minor Planet Center. Retrieved 13 September 2021.
2. "JPL Small-Body Database Browser: 307261 (2002 MS4)" (2020-06-28 last obs.). Jet Propulsion Laboratory. Retrieved 18 June 2022.
3. Gladman, Brett; Marsden, Brian G.; VanLaerhoven, Christa (2008). "Nomenclature in the Outer Solar System" (PDF). The Solar System Beyond Neptune. University of Arizona Press. pp. 43–57. arXiv:astro-ph/0702538. Bibcode:2008ssbn.book...43G. ISBN 9780816527557. S2CID 14469199.
4. Buie, Marc W. "Orbit Fit and Astrometric record for 307261". Southwest Research Institute. from the original on 27 June 2021. Retrieved 13 September 2021.
5. "JPL Horizons On-Line Ephemeris for 307261 (2002 MS4) from 2123-Jan-01 to 2124-Jan-01". JPL Horizons On-Line Ephemeris System. Jet Propulsion Laboratory. Retrieved 28 June 2022. (Perihelion occurs when deldot changes from negative to positive. Uncertainty in time of perihelion is 1-sigma from JPL Small-Body Database.)
6. "JPL Horizons On-Line Ephemeris for 307261 (2002 MS4) at epoch JD 2460000.5". JPL Horizons On-Line Ephemeris System. Jet Propulsion Laboratory. Retrieved 19 June 2022. Solution using the Solar System Barycenter. Ephemeris Type: Elements and Center: @0)
7. "2020/08/08 - 307261 - 2002 MS4 - 4UC419-096262". euraster.net. Euraster. 16 August 2020. Retrieved 31 August 2020.
8. Rommel, Flavia L.; Braga-Ribas, Felipe; Vara-Lubiano, Mónica; Ortiz, Jose L.; Desmars, Josselin; Morgado, Bruno E.; et al. (September 2021). Evidence of topographic features on (307261) 2002 MS4 surface. 15th Europlanet Science Congress 2021. Europlanet Society. Bibcode:2021EPSC...15..440R. doi:10.5194/epsc2021-440. EPSC2021-440. Retrieved 13 September 2021.
9. Thirouin, Audrey (2013). Study of Trans-Neptunian Objects using photometric techniques and numerical simulations (PDF) (Thesis). University of Granada. pp. 92–95. S2CID 125259956. Retrieved 19 November 2019.
10. Verbiscer, Anne J.; Helfenstein, Paul; Porter, Simon B.; Benecchi, Susan D.; Kavelaars, J. J.; Lauer, Tod R.; et al. (April 2022). "The Diverse Shapes of Dwarf Planet and Large KBO Phase Curves Observed from New Horizons". The Planetary Science Journal. 3 (4): 31. Bibcode:2022PSJ.....3...95V. doi:10.3847/PSJ/ac63a6. 95.
11. Tegler, S. C.; Romanishin, W.; Consolmagno, G. J. (December 2016). "Two Color Populations of Kuiper Belt and Centaur Objects and the Smaller Orbital Inclinations of Red Centaur Objects". The Astronomical Journal. 152 (6): 13. Bibcode:2016AJ....152..210T. doi:10.3847/0004-6256/152/6/210. S2CID 125183388. 210.
12. "(307261) 2002MS4 Ephemerides". Asteroids Dynamic Site. Department of Mathematics, University of Pisa, Italy. Retrieved 19 November 2019.
13. Vilenius, E.; Kiss, C.; Mommert, M.; Müller, T.; Santos-Sanz, P.; Pal, A.; et al. (May 2012). ""TNOs are Cool": A survey of the trans-Neptunian region VI. Herschel/PACS observations and thermal modeling of 19 classical Kuiper belt objects" (PDF). Astronomy & Astrophysics. 541: 17. arXiv:1204.0697. Bibcode:2012A&A...541A..94V. doi:10.1051/0004-6361/201118743. S2CID 54222700. A94.
14. Trujillo, C. A.; Brown, M. E. (June 2003). "The Caltech Wide Area Sky Survey". Earth, Moon, and Planets. 92 (1): 99–112. Bibcode:2003EM&P...92...99T. doi:10.1023/B:MOON.0000031929.19729.a1. S2CID 189905639.
15. Schilling, Govert (2008). The Hunt For Planet X. Springer. p. 214. ISBN 978-0-387-77804-4.
16. Trujillo, C. A.; Brown, M. E.; Helin, E. F.; Pravdo, S.; Lawrence, K.; Hicks, M.; Nash, C.; Jordan, A. B.; Staples, S.; Schwartz, M.; Marsden, B. G. (21 November 2002). "MPEC 2002-W27 : 2002 MS4, 2002 QX47, 2002 VR128". Minor Planet Electronic Circular. Minor Planet Center. 2002-W27. Bibcode:2002MPEC....W...27T. Retrieved 26 August 2009.
17. "MPEC 2003-M44 : 2002 KW14, 2002 MS4". Minor Planet Electronic Circular. Minor Planet Center. 29 May 2003. Retrieved 20 June 2022.
18. Lowe, Andrew. "(307261) 2002 MS₄ Precovery Images". andrew-lowe.ca. Retrieved 20 June 2022.
19. "M.P.S. 231732" (PDF). Minor Planet Circulars Supplement. Minor Planet Center (231732): 42. 30 December 2007. Retrieved 19 November 2019.
20. "M.P.C. 77416" (PDF). Minor Planet Circulars. Minor Planet Center (77416): 292. 10 December 2011. Retrieved 20 June 2022.
21. "Rules and Guidelines for Naming Non-Cometary Small Solar-System Bodies" (PDF). IAU Working Group Small Body Nomenclature. 20 December 2021. p. 10. Retrieved 20 June 2022.
22. Rommel, Flavia Luane; Braga-Ribas, Felipe; Pereira, Crystian Luciano; Desmars, Josselin; Santos-Sanz, Pablo; Benedetti-Rossi Rossi, Gustavo; et al. (September 2020). Results on stellar occultations by (307261) 2002 MS4. 14th Europlanet Science Congress 2020. Europlanet Society. Bibcode:2020EPSC...14..866L. doi:10.5194/epsc2020-866. EPSC2020-866. Retrieved 6 September 2021.
23. Zemouri, Rami; Ceravolo, Peter; Kavelaars, JJ; Bridges, Terry (March 2022). "Report on Three Stellar Occultations by the Excited Kuiper Belt Object 2002 MS4". Research Notes of the AAS. 6 (3): 59. Bibcode:2022RNAAS...6...59Z. doi:10.3847/2515-5172/ac5f3b. 59.
24. "JPL Horizons On-Line Ephemeris for 307261 (2002 MS4) at epochs JD 2450000.5–2460000.5". JPL Horizons On-Line Ephemeris System. Jet Propulsion Laboratory. Retrieved 28 June 2022. Solution using the Sun. Ephemeris Type: Elements and Center: @sun)
25. "JPL Horizons On-Line Ephemeris for 307261 (2002 MS4) from 1853-Jan-01 to 1854-Jan-01". JPL Horizons On-Line Ephemeris System. Jet Propulsion Laboratory. Retrieved 28 June 2022. (Perihelion occurs when deldot changes from negative to positive. Uncertainty in time of perihelion is 1-sigma from JPL Small-Body Database.)
26. Lykawka, Patryk Sofia; Tadashi, Mukai (July 2007). "Dynamical classification of trans-neptunian objects: Probing their origin, evolution, and interrelation". Icarus. 189 (1): 213–232. Bibcode:2007Icar..189..213L. doi:10.1016/j.icarus.2007.01.001. S2CID 122671996.
27. Stansberry, John; Grundy, Will; Brown, Mike; Cruikshank, Dale; Spencer, John; Trilling, David; Margot, Jean-Luc (2008). "Physical Properties of Kuiper Belt and Centaur Objects: Constraints from the Spitzer Space Telescope" (PDF). The Solar System Beyond Neptune. University of Arizona Press. pp. 161–179. arXiv:astro-ph/0702538. Bibcode:2008ssbn.book..161S. ISBN 9780816527557. S2CID 578439.
28. Brucker, M. J.; Grundy, W. M.; Stansberry, J. A.; Spencer, J. R.; Sheppard, S. S.; Chiang, E. I.; Buie, M. W. (May 2009). "High albedos of low inclination Classical Kuiper belt objects" (PDF). Icarus. 201 (1): 284–294. arXiv:0812.4290. Bibcode:2009Icar..201..284B. doi:10.1016/j.icarus.2008.12.040. S2CID 53543791.
29. Barucci, M. A.; Belskaya, I.; Fulchignoni, M.; Birlan, M. (September 2005). "Taxonomy of Centaurs and Trans-Neptunian Objects". The Astronomical Journal. 130 (3): 1291–1298. Bibcode:2005AJ....130.1291B. doi:10.1086/431957. S2CID 32008426.
30. "(307261) 2002 MS4, 2019 Aug 19 occultation". IOTA Asteroid Occultation Results Webpage. International Occultation Timing Association. 19 August 2019. Retrieved 19 November 2019.
31. "2002 MS4 08/08/2020". ERC Lucky Star project. Retrieved 6 September 2021.
32. Brown, Michael E. (23 February 2021). "How many dwarf planets are there in the outer solar system?". California Institute of Technology. Retrieved 13 September 2021.
33. Grundy, W. M.; Noll, K. S.; Buie, M. W.; Benecchi, S. D.; Ragozzine, D.; Roe, H. G. (December 2019). "The Mutual Orbit, Mass, and Density of Transneptunian Binary Gǃkúnǁʼhòmdímà ((229762) 2007 UK₁₂₆)" (PDF). Icarus. 334: 30–38. Bibcode:2019Icar..334...30G. doi:10.1016/j.icarus.2018.12.037. S2CID 126574999.
34. Lakdawalla, E. (24 January 2018). "New Horizons prepares for encounter with 2014 MU69". The Planetary Society. Retrieved 13 November 2019.
35. Verbiscer, A.; Porter, S.; Spencer, J.R.; Buie, M.W.; et al. (2017), "New Horizons High-Phase Observations of Distant Kuiper Belt Objects", AGU Fall Meeting Abstracts, 2017: P11C–2528, Bibcode:2017AGUFM.P11C2528V

External links

• 2002 MS4 Precovery Images
• (307261) 2002 MS4
• (307261) 2002 MS4 at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters