S/2015 (136472) 1

S/2015 (136472) 1
Makemake and its moon S/2015 (136472) 1 (arrow)
Discovery[1]
Discovered by
Discovery date27 April 2015
Designations
MK2 (unofficial nickname)[2]
Orbital characteristics[3]
22250±780 km[3]
Eccentricity≈0
18.023±0.017 days[3]
Inclination83.7° wrt Earth line of sight[3]
63°–87° wrt ecliptic (prograde)[1]: 3 
Satellite ofMakemake
Physical characteristics
~175 km (4% albedo; best fit)[1]: 4 
175–250 km (2–4% albedo)[a]
87.5 km
Albedo0.04 (best fit)[1]: 4 
0.02–0.04[1]: 4 
25.0[4]
7.89±0.04[1]: 3 

S/2015 (136472) 1, unofficially nicknamed MK2 by the discovery team,[2] is the only known moon of the trans-Neptunian dwarf planet Makemake.[1][5] It is a dark object about 175 km (110 mi) in diameter, orbiting 22,250 km (13,800 mi) away from Makemake with an orbital period of 18 days.[3] Observations leading to its discovery occurred in April 2015, using the Hubble Space Telescope's Wide Field Camera 3, and its discovery was announced on 26 April 2016.[2]

Physical characteristics

S/2015 (136472) 1 is extremely faint, with an apparent magnitude of 25 in visible light.[4] The satellite is 1,300 times fainter than Makemake, corresponding to a magnitude difference of 7.80.[6][1]: 3 

Prior to the discovery of S/2015 (136472) 1, measurements of Makemake's far-infrared thermal emission by the Spitzer and Herschel space telescopes showed that the dwarf planet emits more thermal radiation than expected for its size and brightness in visible light.[5] This led astronomers to suspect that Makemake must have extra dark surface area that is contributing to this excess thermal emission.[1]: 3  Makemake does not exhibit significant variations in brightness as it rotates, which leaves the possibilities that some of this dark surface area may either be uniformly distributed on Makemake's surface or is located on satellites orbiting Makemake.[5][1]: 3 [7]: 6  The discovery of S/2015 (136472) 1 lends credibility to the hypothesis that Makemake's excess thermal emission largely comes from satellites with dark surfaces.[7]: 6 

Assuming S/2015 (136472) 1 has a uniformly dark surface, the satellite has a geometric albedo or visible light reflectivity of 2–4%, which makes it as dark as charcoal.[1]: 3–4 [6] The satellite is exceptionally dark compared to Makemake's geometric albedo of 82%; this may be because the satellite's gravity is too weak to hold on to bright, volatile ices as they sublimate off the satellite's surface into space.[1]: 4 [6] S/2015 (136472) 1 is estimated to have a diameter of 175 to 250 km (109 to 155 mi), based on its geometric albedo and brightness in visible light.[a] Within this range, S/2015 (136472) 1's diameter is most likely 175 km (109 mi) for a geometric albedo of 4%.[1]: 4  If S/2015 (136472) 1 has the same density as Makemake, then it would contribute less than 0.2% of the total system mass.[1]: 4 

Orbit

S/2015 (136472) 1 follows a likely circular orbit around Makemake with an orbital period of 18 days and a semi-major axis of 22,250 ± 780 km (13,830 ± 480 mi).[3] The satellite's orbit is oriented edge-on from the point of view of Earth-based observatories,[8] meaning that the satellite appears to pass in front of or behind Makemake.[3] This would make the satellite difficult to detect because it would be lost in Makemake's glare most of the time; this is the reason why the satellite was not seen in earlier telescope observations.[1] Although it is ambiguous whether the satellite is orbiting Makemake in the prograde or retrograde direction, the satellite's orbital inclination with respect to Earth's line of sight suggests that it may have been eclipsing and occulting Makemake 7±2 years before or after January 2018.[3]

Name

See also: Makemake (deity)

As of 2025, the satellite has no official name.[9] The designation S/2015 (136472) 1 is the satellite's provisional designation, with "S/" indicating satellite, "2015" being the satellite's year of discovery, and "1" being the satellite's order of discovery in that year.[10] "(136472)" is Makemake's minor-planet number.[11]

The nickname 'MK2' simply means object 2 in the Makemake system. A permanent name may be chosen from an associated figure in the mythology of Easter Island.

Notes

  1. ^ a b For a nominal absolute magnitude of 7.8, a geometric albedo of 0.02 gives a diameter of 250 km (160 mi)[1]: 3  while a geometric albedo of 0.04 gives a diameter of 175 km (109 mi).[1]: 4 

References

  1. ^ a b c d e f g h i j k l m n o p q Parker, A. H.; Buie, M. W.; Grundy, W. M.; Noll, K. S. (25 April 2016). "Discovery of a Makemakean Moon". The Astrophysical Journal. 825 (1): L9. arXiv:1604.07461. Bibcode:2016ApJ...825L...9P. doi:10.3847/2041-8205/825/1/L9. S2CID 119270442.
  2. ^ a b c "HubbleSite – NewsCenter – Hubble Discovers Moon Orbiting the Dwarf Planet Makemake (04/26/2016) – The Full Story". hubblesite.org. Retrieved 14 July 2022.
  3. ^ a b c d e f g h Bamberger, Daniel. "A preliminary orbit for the satellite of dwarf planet (136472) Makemake". arXiv:2509.05880 [astro-ph.EP].
  4. ^ a b William M. Grundy (13 February 2020). "Makemake (136472 2005 FY9)". Lowell Observatory. Archived from the original on 21 February 2020. Retrieved 20 February 2020.
  5. ^ a b c Parker, A. (2 May 2016). "A Moon for Makemake". Planetary Society blogs. Planetary Society. Retrieved 2 May 2016.
  6. ^ a b c Mike Wall (26 April 2016). "Distant Dwarf Planet Makemake Has Its Own Moon". Space.com. Retrieved 26 April 2016.
  7. ^ a b T. A. Hromakina; I. N. Belskaya; Yu. N. Krugly; V. G. Shevchenko; J. L. Ortiz; P. Santos-Sanz; R. Duffard; N. Morales; A. Thirouin; R. Ya. Inasaridze; V. R. Ayvazian; V. T. Zhuzhunadze; D. Perna; V. V. Rumyantsev; I. V. Reva; A. V. Serebryanskiy; A. V. Sergeyev; I. E. Molotov; V. A. Voropaev; S. F. Velichko (9 April 2019). "Long-term photometric monitoring of the dwarf planet (136472) Makemake". Astronomy & Astrophysics. 625: A46. arXiv:1904.03679. Bibcode:2019A&A...625A..46H. doi:10.1051/0004-6361/201935274. S2CID 102350991.
  8. ^ Green, Daniel W. E. (26 April 2016). "S/2015 (136472) 1". Central Bureau Electronic Telegram. 4275 (4275). Central Bureau for Astronomical Telegrams: 1. Bibcode:2016CBET.4275....1P.
  9. ^ "JPL Small-Body Database Browser: 136472 Makemake (2005 FY9)". NASA Jet Propulsion Laboratory (2019-05-12 last obs). Archived from the original on 16 June 2019. Retrieved 20 February 2020.
  10. ^ "Naming of Astronomical Objects". International Astronomical Union. Archived from the original on 31 October 2013. Retrieved 8 July 2017.
  11. ^ International Astronomical Union (19 July 2008). "Fourth dwarf planet named Makemake" (Press release). International Astronomical Union (News Release – IAU0806). Archived from the original on 23 July 2008. Retrieved 20 July 2008.
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