174567 Varda

174567 Varda
	Hubble Space Telescope image of Varda and its satellite Ilmarë, taken in 2010 and 2011
Discovery
Discovered by	J. A. Larsen
Discovery site	Kitt Peak National Obs.
Discovery date	21 June 2003
Designations
Designation	(174567) Varda
Pronunciation	/ˈvɑːrdə/
Named after	Varda; (figure by J. R. R. Tolkien)
Alternative names	2003 MW12
Minor planet category	TNO · cubewano; detached · distant
Symbol	(astrological)
Orbital characteristics
	Epoch 31 May 2020 (JD 2459000.5)
	Uncertainty parameter 2
Observation arc	39.12 yr (14,290 d)
Earliest precovery date	19 March 1980
Aphelion	52.711 AU
Perihelion	39.510 AU
Semi-major axis	46.110 AU
Eccentricity	0.14315
Orbital period (sidereal)	313.12 yr (114,366 d)
Mean anomaly	275.208°
Mean motion	0° 0m 11.332s / day
Inclination	21.511°
Longitude of ascending node	184.151°
Time of perihelion	≈ 1 November 2096; ±4 days
Argument of perihelion	180.072°
Known satellites	1 (Ilmarë)
Physical characteristics
Mean diameter	740±14 km (area equivalent); 722+82; −76 km
Flattening	0.080±0.049 (for period of 11.82 h); or 0.235±0.050 (for period of 5.91 h)
Mass	(2.45±0.06)×1020 kg
Mean density	1.23±0.04 g/cm3 (for period of 11.82 h); 1.78±0.06 g/cm3 (for period of 5.61 h)
Synodic rotation period	5.61 h or 5.91 h (single-peaked); 11.82 h (double-peaked)
Albedo	0.099±0.002 (primary); 0.102+0.024; −0.024
Spectral type	IR (moderately red); B−V=0.886±0.025; V–R=0.55±0.02; V−I=1.156±0.029
Apparent magnitude	20.5
Absolute magnitude (H)	3.81±0.01 (primary); 3.097±0.060; 3.4

174567 Varda (provisional designation 2003 MW₁₂) is a binary trans-Neptunian planetoid of the resonant hot classical population of the Kuiper belt, located in the outermost region of the Solar System.^[1] Its moon, Ilmarë, was discovered in 2009.^[13]

Astronomer Michael Brown estimates that, with an absolute magnitude of 3.5 and a calculated diameter of approximately 700–800 kilometers (430–500 miles),^[14]^[15] it is likely a dwarf planet.^[16] However, William M. Grundy et al. argue that objects in the size range of 400–1000 km, with albedos less than ≈0.2 and densities of ≈1.2 g/cm³ or less, have likely never compressed into fully solid bodies, let alone differentiated, and so are highly unlikely to be dwarf planets.^[17] It is not clear if Varda has a low or a high density.

Discovery and orbit

Varda was discovered in March 2006, using imagery dated from 21 June 2003, by Jeffrey A. Larsen with the Spacewatch telescope as part of a United States Naval Academy Trident Scholar project.^[18]

It orbits the Sun at a distance of 39.5–52.7 AU once every 313.1 years (over 114,000 days; semi-major axis of 46.1 AU). Its orbit has an eccentricity of 0.14 and an inclination of 21.5° with respect to the ecliptic.^[1] As of November 2019^[update], Varda is 47.5 AU from the Sun.^[12] It will come to perihelion around November 2096.^[6] It has been observed 321 times over 23 oppositions, with precovery images back to 1980.^[1]^[2]

Name

The names for Varda and its moon were announced by the Minor Planets Center on 16 January 2014. Varda (Quenya: [ˈvarda]) is the queen of the Valar, creator of the stars, one of the most powerful servants of almighty Eru Ilúvatar in J. R. R. Tolkien's fictional mythology. Ilmarë is a chief of the Maiar and Varda's handmaiden.^[2]

The use of planetary symbols is discouraged in astronomy, so Varda never received a symbol in the astronomical literature. There is no standard symbol for Varda used by astrologers either. Zane Stein proposed a gleaming star as the symbol ().^[19]

Satellite

Varda has one known satellite, Ilmarë (or Varda I), which was discovered in 2009. It is estimated to be about 350 km in diameter (about 50% that of its primary), constituting 8% of the system mass, or 2×10¹⁹ kg, assuming its density and albedo are the same as that of Varda.^[b]

The Varda–Ilmarë system is tightly bound, with a semimajor axis of 4809±39 km (about 12 Varda radii) and an orbital period of 5.75 days.

Physical properties

Based on its apparent brightness and assumed albedo, the estimated combined size of the Varda–Ilmarë system is 792+91
−84 km, with the size of the primary estimated at 722+82
−76 km.^[8] The total mass of the binary system is approximately 2.66×10²⁰ kg. The density of both the primary and the satellite is estimated at 1.24 g/cm³, assuming that they have equal density.^[10]^[8] On the other hand, if the density or albedo of the satellite is lower than that of primary then the density of Varda will be higher up to 1.31 g/cm³.^[8]

On 10 September 2018, Varda's projected diameter was measured to be 766±6 km via a stellar occultation, with a projected oblateness of 0.066±0.047. The equivalent diameter is 740 km, consistent with previous measurements.^[7] Given Varda's equivalent diameter derived from the occultation, its geometric albedo is measured at 0.099, making it as dark as the large plutino 2003 AZ84.

The rotation period of Varda is unknown; it has been estimated at 5.61 hours in 2015,^[8] and more recently (in 2020) as either 4.76, 5.91 (the most likely value), 7.87 hours, or twice those values.^[7] The large uncertainty in Varda's rotation period yields various solutions for its density and true oblateness; given a most likely rotation period of 5.91 or 11.82 hours, its bulk density and true oblateness could be either 1.78±0.06 g/cm³ and 0.235 or 1.23 g/cm³ and 0.080, respectively.^[7]

The surfaces of both the primary and the satellite appear to be red in the visible and near-infrared parts of the spectrum (spectral class IR), with Ilmarë being slightly redder than Varda. The spectrum of the system does not show water absorption but shows evidence of methanol ice.^{[citation needed]}

Notes

^ Assuming equal albedos for the primary and the secondary
^ ^a ^b Using Grundy et al.'s working diameters of 361 km and 163 km, and assuming the densities of the two bodies are equal, Varda would contribute 91.6% of the system mass of (2.664±0.064)×10²⁰ kg.^[8]

References

^ ^a ^b ^c ^d ^e ^f ^g "JPL Small-Body Database Browser: 174567 Varda (2003 MW12)" (2019-05-04 last obs.). Jet Propulsion Laboratory. 30 May 2019. Retrieved 20 February 2020.
^ ^a ^b ^c ^d ^e "174567 Varda (2003 MW12)". Minor Planet Center. Retrieved 24 November 2019.
^ "List of Transneptunian Objects". Minor Planet Center. Retrieved 5 June 2018.
^ "MPEC 2009-P26 :Distant Minor Planets (2009 AUG. 17.0 TT)". Minor Planet Center. 7 August 2009. Retrieved 24 August 2009.
^ Marc W. Buie. "Orbit Fit and Astrometric record for 174567". SwRI (Space Science Department). Retrieved 24 November 2019.
^ ^a ^b JPL Horizons Observer Location: @sun (Perihelion occurs when deldot changes from negative to positive. Uncertainty in time of perihelion is 3-sigma.)
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k Souami, D.; Braga-Ribas, F.; Sicardy, B.; Morgado, B.; Ortiz, J. L.; Desmars, J.; et al. (August 2020). "A multi-chord stellar occultation by the large trans-Neptunian object (174567) Varda". Astronomy & Astrophysics. 643: A125. arXiv:2008.04818. Bibcode:2020A&A...643A.125S. doi:10.1051/0004-6361/202038526. S2CID 221095753.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k Grundy, W. M.; Porter, S. B.; Benecchi, S. D.; Roe, H. G.; Noll, K. S.; Trujillo, C. A.; et al. (September 2015). "The mutual orbit, mass, and density of the large transneptunian binary system Varda and Ilmarë". Icarus. 257: 130–138. arXiv:1505.00510. Bibcode:2015Icar..257..130G. doi:10.1016/j.icarus.2015.04.036. S2CID 44546400.
^ ^a ^b Thirouin, A.; Noll, K. S.; Ortiz, J. L.; Morales, N. (September 2014). "Rotational properties of the binary and non-binary populations in the trans-Neptunian belt". Astronomy and Astrophysics. 569: 20. arXiv:1407.1214. Bibcode:2014A&A...569A...3T. doi:10.1051/0004-6361/201423567. S2CID 119244456.
^ ^a ^b 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". Astronomy & Astrophysics. 541: 17. arXiv:1204.0697. Bibcode:2012A&A...541A..94V. doi:10.1051/0004-6361/201118743. S2CID 54222700.
^ Tegler, S. C.; Romanishin, R. W.; Consolmalgo, J. S. (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.
^ ^a ^b "AstDys (174567) Varda Ephemerides". Department of Mathematics, University of Pisa, Italy. Archived from the original on 24 November 2019. Retrieved 24 November 2019.
^ Johnston, Wm. Robert (31 January 2015). "Asteroids with Satellites Database – (174567) Varda and Ilmare". Johnston's Archive. Retrieved 5 June 2018.
^ Ceravolo, D.; Ceravolo, P. (26 July 2019). "(174567) Varda, 2018 September 10 occultation". asteroidoccultation.com. Retrieved 28 November 2019.
^ Braga-Ribas, Felipe; Sicardy, Bruno; Assafin, Marcelo; Ortiz, José-Luis; Camargo, Julio; Desmars, Josselin; et al. (September 2019). The stellar occultation by the TNO (174567) Varda of September 10, 2018: size, shape and atmospheric constraints (PDF). EPSC-DPS Joint Meeting 2019. Vol. 13. European Planetary Science Congress. Retrieved 14 October 2019.
^ Brown, Michael E. "How many dwarf planets are there in the outer solar system?". California Institute of Technology. Retrieved 9 February 2018.
^ W.M. Grundy, K.S. Noll, M.W. Buie, S.D. Benecchi, D. Ragozzine & H.G. Roe, 'The Mutual Orbit, Mass, and Density of Transneptunian Binary Gǃkúnǁʼhòmdímà ((229762) 2007 UK₁₂₆)', Icarus (forthcoming, available online 30 March 2019) Archived 7 April 2019 at the Wayback Machine DOI: 10.1016/j.icarus.2018.12.037,
^ Larsen, Jeffrey A.; Roe, Eric A.; Albert, C. Elise; et al. (2007). "The Search for Distant Objects in the Solar System Using Spacewatch". The Astronomical Journal. 133 (4): 1247–1270. Bibcode:2007AJ....133.1247L. doi:10.1086/511155.
^ Miller, Kirk (26 October 2021). "Unicode request for dwarf-planet symbols" (PDF). unicode.org.