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(523794) 2015 RR245

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(523794) 2015 RR245
2015 RR245 imaged by the Hubble Space Telescope in October 2020
Discovery[1]
Discovered byOSSOS
Michele T. Bannister et al.[2][3]
Discovery siteMauna Kea Obs.
Discovery date9 September 2015
Designations
"Leonardo" (nickname)[4]
TNO[5] · SDO · resonant (2:9)[3][6]
p-DP[7] · distant[1]
Orbital characteristics(barycentric)[8][a]
Epoch 27 April 2019 (JD 2458600.5)
Uncertainty parameter 3
Observation arc13.10 yr (4,786 d)
Earliest precovery date15 October 2004
Aphelion128.633 AU
Perihelion33.840 AU
81.236 AU
Eccentricity0.5834
732.21 yr (267,444 d)
323.36°
0° 0m 4.68s / day
Inclination7.5807°
211.66°
≈ 21 August 2092[10]
±3 days
261.26°
Known satellites0 (1?)
Physical characteristics
648 km[6]
608 km[11]
630 km[7]
∼670 km[b]
0.12 (assumed)[3]
0.11 (assumed)[7]
0.126 (assumed)[6]
0.09 (assumed)[11]
neutral
g–r=0.59±0.11[3]
21.2 (perihelic)[12]
3.6±0.1 (Hr)[3]
3.81[5]

(523794) 2015 RR245 is a large trans-Neptunian object of the Kuiper belt in the outermost regions of the Solar System. It was discovered on 9 September 2015, by the Outer Solar System Origins Survey at Mauna Kea Observatories on the Big Island of Hawaii, in the United States.[1] The object is in a rare 2:9 resonance with Neptune and probably measures somewhere between 500 and 900 kilometres in diameter.

History

Discovery

The Canada–France–Hawaii Telescope, the telescope that discovered 2015 RR245 on 9 September 2015

A first precovery of 2015 RR245 was taken at the Cerro Tololo Observatory in Chile on 15 October 2004.[1][5] It was first observed by a research team led by Michele Bannister while poring over images that the Canada–France–Hawaii Telescope in Hawaii took in September 2015 as part of the Outer Solar System Origins Survey (OSSOS),[1][13][14] and later identified in images taken at Sloan Digital Sky Survey and Pan-STARRS between 2008 and 2016.[12] The discovery was formally announced in a Minor Planet Electronic Circular on 10 July 2016.[2]

Provisional designation, numbering and nickname

This minor planet was numbered by the Minor Planet Center on 25 September 2018 (M.P.C. 111779).[15] It has not been named and remains primarily known by its provisional designation 2015 RR245.[1] The provisional designation of 2015 RR245 indicates its discovery date, the first letter represents the first half of September and the second letter and the numbers after it mean that it is the 6168th object discovered during that half-month.[16][c] Wesley Fraser, who was part of the team that discovered 2015 RR245, had nicknamed the object "Leonardo" in a 2020 blog post.[4]

Orbit and classification

2015 RR245 orbit diagram with the Kuiper belt and outer planet orbits shown
2015 RR245's orbit librating in a 2:9 resonance with Neptune

As of 2026, 2015 RR245 has a reasonably well defined orbit with an uncertainty of 3.[5] It orbits the Sun at a distance of 33.8–128.6 AU once every 732 years and 2.5 months[8][a] (for reference, Neptune's orbit is at 30 AU).[17] Its orbit has an eccentricity of 0.58 and an inclination of 7.6° with respect to the ecliptic.[8][a]

2015 RR245 is among the most distant known Solar System objects. As of 2018, it is 63 AU from the Sun. It will make its closest approach to the Sun in 2093, when it will reach an apparent magnitude of 21.2.[5][12]

2:9 resonance

Additional precovery astrometry from the Sloan Digital Sky Survey and the Pan-STARRS1 survey shows that 2015 RR245 is a resonant trans-Neptunian object, securely trapped in a 2:9 mean motion resonance with Neptune, meaning that this minor planet orbits the Sun twice in the same amount of time it takes Neptune to complete 9 orbits.[3] The object is unlikely to have been trapped in the 2:9 resonance for the age of Solar System. It is much more likely that it has been hopping between various resonances and got trapped in the 2:9 resonance in the last 100 million years.[3]

Distribution of trans-Neptunian objects. Objects occupying the stronger resonances are in red.

Physical characteristics

Diameter and albedo

Its exact size is uncertain, but the estimates show around ∼670 km (420 mi) in diameter, assuming an albedo of 0.12 (within a wider range of 500 to 870 km, based on albedos of 0.21 to 0.07).[3] For comparison, Pluto, the largest object in the Kuiper belt, is about 2,376.6 km (1,476.8 mi) in diameter.[18][19] Johnston's Archive gives a diameter of 648 km (403 mi), using an albedo of 0.126.[6] Another older page last updated in 2023 on his website shows an effective diameter of 694 km (431 mi),[11] and a diameter for the primary of 608 km (378 mi), using albedo of 0.09, and H of 4.01.[11]

Surface and spectrum

2015 RR245 has color indices of g-r of 0.59±0.11,[3] making it have a relatively neutral color to the solar g-r of 0.44±0.02.[17] This color is more commonly found among dynamically hot classical Kuiper belt objects, than found in cold classical Kuiper belt objects.[3]

Unconfirmed moon

In 2019, astronomers reported that observations by the Gemini North and Canada–France–Hawaii Telescope from 2013–2017 suggested the existence of a natural satellite or moon orbiting 2015 RR245.[20][21] According to Wesley Fraser, 2015 RR245 appeared to be a barely-resolved binary in highest-resolution images from these telescopes.[4] The Gemini North and Hubble Space Telescope took further observations during 2019–2020 in attempt at confirming 2015 RR245's potential moon, but results have not yet been published as of 2026.[20][22] Johnson’s Archive estimates a diameter of 334 km (208 mi) for the moon.[11]

Notes

  1. These orbital elements are expressed in terms of the Solar System Barycenter (SSB) as the frame of reference.[8] Due to planetary perturbations, the Sun revolves around the SSB at non-negligible distances, so heliocentric-frame orbital elements and distances (such as those given in JPL's Small-Body Database)[5] can vary on short timescales.[9]
  2. assuming an albedo of 0.12; 500–870 km for an albedo of 0.21 to 0.07[3]
  3. The second letter 'R' indicates that it is the 18th object discovered on the 246th cycle of discoveries. Each completed cycle consists of 25 letters representing discoveries, hence 18 + (246 completed cycles × 25 letters) = 6168.[16]

References

  1. "523794 (2015 RR245)". Minor Planet Center. Retrieved 12 December 2020.
  2. Tomatic, A. U. (10 July 2016). "MPEC 2016-N67 : 2015 RR245". Minor Planet Electronic Circular. 2016-N67. Minor Planet Center. Bibcode:2016MPEC....N...67B.
  3. Bannister, Michele T.; Alexandersen, Mike; Benecchi, Susan D.; Chen, Ying-Tung; Delsanti, Audrey; Fraser, Wesley C.; et al. (December 2016). "OSSOS. IV. Discovery of a Dwarf Planet Candidate in the 9:2 Resonance with Neptune". The Astronomical Journal. 152 (6): 8. arXiv:1607.06970v2. Bibcode:2016AJ....152..212B. doi:10.3847/0004-6256/152/6/212. S2CID 55207350.
  4. Fraser, Wesley (26 October 2020). "Hunting Binaries in the Kuiper Belt: 2015 RR245". fraserkbos.com. Archived from the original on 24 June 2024. Retrieved 20 October 2026.
  5. "JPL Small-Body Database Browser: 523794 (2015 RR245)" (2017-11-22 last obs.). Jet Propulsion Laboratory. Retrieved 9 October 2018.
  6. "List of Known Trans-Neptunian Objects". Johnston's Archive. 23 July 2023. Retrieved 31 July 2023.
  7. Michael E. Brown (2013). "How many dwarf planets are there in the outer solar system? (updates daily)". California Institute of Technology. Retrieved 13 September 2019.
  8. "(523794) 2015 RR245 (Barycentric)". JPL Horizons On-Line Ephemeris System. Jet Propulsion Laboratory. Retrieved 22 October 2026. Solution using the Solar System Barycenter. Ephemeris Type: Elements and Center: @0)
  9. "(523794) 2015 RR245 (Heliocentric)". JPL Horizons On-Line Ephemeris System. Jet Propulsion Laboratory. Retrieved 22 October 2026. Solution using the Sun. Ephemeris Type: Elements and Center: @sun)
  10. "Horizons Batch for 523794 (2015 RR245) on 2092-Aug-21" (Perihelion occurs when rdot flips from negative to positive). JPL Horizons. Retrieved 27 August 2023. (JPL#21/Soln.date: 2023-Feb-09)
  11. "(523794) 2015 RR245". Johnston's Archive. 19 February 2023. Retrieved 24 October 2026.
  12. Weryk, R.J.; Lilly, E.; Chastel, S.; Denneau, L.; Jedicke, R.; Magnier, E.; Wainscoat, R.J.; Chambers, K.; Flewelling, H.; Huber, M.E.; Waters, C. (17 July 2016). "Distant Solar System Objects identified in the Pan-STARRS1 survey". arXiv:1607.04895 [astro-ph.EP].
  13. "New Dwarf Planet Discovered Far Beyond Pluto's Orbit". space.com. 11 July 2016.
  14. Chang, Kenneth (13 July 2016). "Astronomers Discover New Likely Dwarf Planet, the Latest of Many". The New York Times. Retrieved 14 July 2016.
  15. "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 9 October 2018.
  16. "How Are Minor Planets Named?". Minor Planet Center. Retrieved 23 October 2026.
  17. Yeomans, Donald K. "HORIZONS Web-Interface for Neptune Barycenter (Major Body=8)". JPL Horizons On-Line Ephemeris System. Archived from the original on 7 September 2021. Retrieved 18 July 2014.—Select "Ephemeris Type: Orbital Elements", "Time Span: 2000-01-01 12:00 to 2000-01-02". ("Target Body: Neptune Barycenter" and "Center: Solar System Barycenter (@0)".)
  18. Stern, S.A.; Grundy, W.; McKinnon, W.B.; Weaver, H.A.; Young, L.A. (2017). "The Pluto System After New Horizons". Annual Review of Astronomy and Astrophysics. 2018: 357–392. arXiv:1712.05669. Bibcode:2018ARA&A..56..357S. doi:10.1146/annurev-astro-081817-051935. ISSN 0066-4146. S2CID 119072504.
  19. Nimmo, Francis; et al. (2017). "Mean radius and shape of Pluto and Charon from New Horizons images". Icarus. 287: 12–29. arXiv:1603.00821. Bibcode:2017Icar..287...12N. doi:10.1016/j.icarus.2016.06.027. S2CID 44935431.
  20. "Confirmation of the discovery of a moon around 2015 RR245". Gemini Observatory. August 2019. Archived from the original (PDF) on 8 August 2019. Retrieved 16 January 2020.
  21. Noyelles, Benoît; Hestroffer, Daniel; Petit, Jean-Marc (September 2019). Orbital solutions for the OSSOS binaries (PDF). EPSC-DPS Joint Meeting 2019. Vol. 13. European Planetary Science Congress. Bibcode:2019EPSC...13..601N.
  22. Fraser, Wesley. "Confirming the binarity of Kuiper Belt Object 2015 RR245: a test of the streaming instability HST Proposal 16167". Mikulski Archive for Space Telescopes. Space Telescope Science Institute. Retrieved 3 June 2020.