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(768325) 2015 BP519

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(768325) 2015 BP519
Orbital diagram of 2015 BP519 and other extreme objects along with hypothetical Planet Nine
Discovery[1][2]
Discovered byDark Energy Survey
Discovery siteCerro Tololo Obs.
Discovery date17 January 2015
(first observed only)
Designations
"Caju" (nickname)[a]
TNO[3] · ESDO[4] · ETNO
distant[2]
Orbital characteristics[3]
Epoch 27 April 2019 (JD 2458600.5)
Uncertainty parameter 5
Observation arc3.22 yr (1,176 d)
Aphelion820 AU
Perihelion35.2 AU
428.03 AU
Eccentricity0.9178
8856 yr (3,234,488 d)
358.39°
0° 0m 0.36s / day
Inclination54.125°
135.11°
≈ 7 September 2058[5]
±1 month
348.37°
Known satellites0
Physical characteristics
524 km (est.)[6]
516 km (est.)[4]
400–700 km (est.)[7]
719+309
−208 km (from assumed albedo)[8]
0.08 (assumed)[6]
0.124 (assumed)[4]
0.07 to 0.21 (assumed)[7]
g–r = 0.79±0.17[7]
r–i = 0.19±0.12
r–z = 0.42±0.15
i–z = 0.23±0.15
21.5
4.32[2][3]

(768325) 2015 BP519, internally nicknamed Caju,[a] is an extreme trans-Neptunian object from the scattered disc on a highly eccentric and inclined orbit in the outermost region of the Solar System.[7] It has been described as an extended scattered disc object (ESDO),[4] and fits into the group of extreme objects that led to the prediction of Planet Nine, and has the highest orbital inclination of any of these objects.[a]

The diameter of 2015 BP519 is estimated to be 719+309
−208 km.[8]

History

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Discovery and observations

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The 4.0-meter Víctor M. Blanco Telescope at Cerro Tololo Observatory, which houses the Dark Energy Camera (DECam)

2015 BP519 was first observed on 17 January 2015, by astronomers with the Dark Energy Survey at Cerro Tololo Observatory (W84) in Chile.[1][2] The body's observation arc begins with a precovery taken on 27 November 2014 by astronomers with the Dark Energy Survey using the DECam instrument of the Víctor M. Blanco Telescope at Cerro Tololo Inter-American Observatory in Chile.[2] Its discovery was reported in a paper published by Dark Energy Survey astronomers in 2018.[7]

Naming

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As of 2026, 2015 BP519 has not been named, but it is nicknamed Caju ("cashew") by the discovery team.[a]

Orbit and classification

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This image shows the plot of eccentricity and perihelion of trans-Neptunian objects, colored by their main dynamical categories. 2015 BP519 is shown at the top, left of 2017 OF201.

Orbital characteristics

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2015 BP519 orbits the Sun at a distance of 35.2–821 AU once every 8856 years (3,234,488 days; semi-major axis of 428 AU). Its orbit has an exceptionally high eccentricity of 0.92 and an inclination of 54° with respect to the ecliptic.[3] This makes it a probable outlier among the known extreme trans-Neptunian objects.[3][9] It has been described as an extended scattered disc object (ESDO).[4]

Planet Nine hypothesis

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2015 BP519 fits into the group of extreme trans-Neptunian objects that originally led to the prediction of Planet Nine.[a]: 13  The group consists of more than a dozen bodies with a perihelion greater than 30 AU and a semi-major axis greater than 250 AU, with 2015 BP519 having the highest orbital inclination of any of these objects.[a] Subsequently, unrefereed work by de la Fuente Marcos (2018) found that 2015 BP519's current orbital orientation in space is not easily explained by the same mechanism that keeps other extreme trans-Neptunian objects together, suggesting that the clustering in its orbital angles cannot be attributed to Planet Nine's influence.[9] However, regardless of the current direction of its orbit, its high orbital inclination appears to fit into the class of high-semi major axis, high-inclination objects predicted by Batygin & Morbedelli (2017) to be generated by Planet Nine.

Physical characteristics

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Size and albedo

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According to the original paper for the discovery of the object, its diameter is estimated to be 400 km to 700 km, using a albedo of 0.07 to 0.21.[7] However, according to Michael Brown and Johnston's Archive, 2015 BP519 measures 524 and 516 kilometers in diameter based on an assumed albedo of 0.08 and 0.124, respectively.[6][4] A newer 2025 study estimated its diameter at 719+309
−208 km assuming a median geometric albedo, which is bigger than previously thought.[8]

Spectra and surface

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2015 BP519 has color indices of: g-r 0.79 ± 0.17, r-i 0.19 ± 0.12, r-z 0.42 ± 0.15 and i-z 0.23 ± 0.15.[7] The color of 2015 BP519 is moderately red.[7]

Upcoming observations

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As of 2018, no rotational lightcurve of has been obtained from photometric observations. The body's rotation period, pole and shape remain unknown.[3] It has not yet been imaged by high-resolution telescopes, so it has no known moons.[10] The Hubble Space Telescope is planned to image 2015 BP519 in 2026, which should determine if it has significantly sized moons.[10]

See also

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Notes

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  1. 1 2 3 4 5 6 The nickname "Caju" is mentioned in the downloadable PowerPoint presentation "Evaluating the Dynamical Stability of Outer Solar System Objects in the Presence of Planet Nine", by Juliette Becker, Fred Adams, Tali Khain, Stephanie Hamilton, and David Gerdes at University of Michigan.

References

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  1. 1 2 "List Of Centaurs and Scattered-Disk Objects". Minor Planet Center. Retrieved 9 February 2018.
  2. 1 2 3 4 5 "2015 BP519". Minor Planet Center. Retrieved 10 May 2018.
  3. 1 2 3 4 5 6 "JPL Small-Body Database Browser: (2015 BP519)" (2018-02-15 last obs.). Jet Propulsion Laboratory. Retrieved 10 May 2018.
  4. 1 2 3 4 5 6 "List of Known Trans-Neptunian Objects". Johnston's Archive. 7 October 2018. Retrieved 23 October 2018.
  5. ↑ JPL Horizons Observer Location: @sun (Perihelion occurs when deldot changes from negative to positive. Uncertainty in time of perihelion is 3-sigma.)
  6. 1 2 3 Brown, Michael E. "How many dwarf planets are there in the outer solar system?". California Institute of Technology. Retrieved 23 October 2018.
  7. 1 2 3 4 5 6 7 8 Becker, J. C.; Khain, T.; Hamilton, S. J.; Adams, F. C.; Gerdes, D. W.; Zullo, L.; et al. (August 2018). "Discovery and Dynamical Analysis of an Extreme Trans-Neptunian Object with a High Orbital Inclination". The Astronomical Journal. 156 (2): 17. arXiv:1805.05355. Bibcode:2018AJ....156...81B. doi:10.3847/1538-3881/aad042. S2CID 55163842.
  8. 1 2 3 Ferreira, Feliphe S.; Camargo, Julio I. B.; Boufleur, Rodrigo; Banda-Huarca, M. V.; Pieres, Adriano; Peixoto, Viviane F.; Assafin, Marcelo; Bernardinelli, P. H.; Lin, H. W.; Braga-Ribas, Felipe; Gomes-Junior, Altair; Vieira-Martins, Roberto; Costa, da; Abbott, T. M. C.; Aguena, M.; Allam, Sahar S.; Alves, O.; Annis, J.; Bacon, D.; Brooks, D.; Burke, D. L.; Rosell, A. Carneiro; Carretero, J.; Desai, S.; Doel, P.; Everett, S.; Ferrero, I.; Frieman, J.; García-Bellido, J.; Gatti, M.; Gaztanaga, E.; Giannini, G.; Gruen, D.; Gruendl, R. A.; Herner, K.; Hinton, S. R.; Hollowood, D. L.; Honscheid, K.; James, D. J.; Kuehn, K.; Lee, S.; Marshall, J. L.; Mena-Fernández, J.; Miquel, R.; Myles, J.; Palmese, A.; Malagón, A. A. Plazas; Pereira, M. E. S.; Samuroff, S.; Sanchez, E.; Cid, D. Sanchez; Servila-Noarbe, I.; Smith, M.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; To, C.; Tucker, D. L.; Vicente, de; Vikram, V.; Walker, A. R.; Weaverdyck, N.; Collaboration, DES (23 April 2025). "Year six photometric measurements of known Trans-Neptunian Objects and Centaurs by the Dark Energy Survey". arXiv.org. Retrieved 8 October 2026.
  9. 1 2 de la Fuente Marcos, Carlos; de la Fuente Marcos, Raúl (September 2018). "A Fruit of a Different Kind: 2015 BP519 as an Outlier Among the Extreme Trans-neptunian Objects". Research Notes of the American Astronomical Society. 2 (3): 167. arXiv:1809.02571. Bibcode:2018RNAAS...2c.167D. doi:10.3847/2515-5172/aadfec. S2CID 119433944.
  10. 1 2 Proudfoot, Benjamin (August 2025). "A Search For The Moons of Mid-Sized TNOs". Mikulski Archive for Space Telescopes. Space Telescope Science Institute: HST Proposal 18010. Cycle 33. Retrieved 17 August 2025.
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