20000 Varuna

:"This article is about 20000 Varuna, a minor planet. For other uses of the word, see Varuna (disambiguation)"Infobox Planet
bgcolour = #FFFFC0
name = 20000 Varuna
symbol =


caption = Artist's conception of Varuna
discovery = yes
discoverer = R. McMillan (Spacewatch)
discovered = 28 November 2000
mp_name = 20000 Varuna
alt_names = mp|2000 WR|106
mp_category = TNO (cubewano)cite web
author=Marc W. Buie
date=2007/01/12
title=Orbit Fit and Astrometric record for 20000
publisher=SwRI (Space Science Department)
url=http://www.boulder.swri.edu/~buie/kbo/astrom/20000.html
accessdate=2008-09-19]
epoch = 14 July 2004 (JD 2453200.5)
aphelion = 6 781.985 Gm (45.335 AU)
perihelion = 6 120.810 Gm (40.915 AU)
semimajor = 6 451.398 Gm (43.129 AU)
semiminor =
orbital_circ =
eccentricity = 0.051
period = 103 440.6 d (283.20 a)
avg_speed = 4.53 km/s
max_speed =
min_speed =
inclination = 17.2°
asc_node = 97.296°
arg_peri = 271.631°
mean_anomaly=89.673°
physical_characteristics = yes
dimensions=800 km (avg of thermals)cite web|url=http://www.johnstonsarchive.net/astro/tnodiam.html |title=TNO/Centaur diameters and albedos |accessdate=2006-11-08 |last=Stansberry |date=2008]
(scalene ellipsoid)?
surface_area =
volume =
mass = ~5.9e|20 kg
density = 0.992 g/cm³Lightcurves Lacerda P., Jewitt D."Dentisities Of Solar System Objects From Their Rotational Lightcurves", accepted to AJ Dec. 2006 [http://www.arxiv.org/abs/astro-ph/0612237 Preprint] ]
surface_grav = 0.15 m/s²
escape_velocity = 0.39 km/s
sidereal_day = 0.132 16 d (3.17 h)
rot_velocity =
albedo = 0.037–0.26
single_temperature = ~43–41 K
spectral_type = (moderately red) B-V=0.93 V-R=0.64 [cite web|url=http://www.psi.edu/pds/asteroid/EAR_A_COMPIL_3_TNO_CEN_COLOR_V3_0/data/tnocencol.tab |title=TNO and Centaur Colors |accessdate=2006-11-08]
magnitude = 19.9 (opposition)cite web
title=HORIZONS Web-Interface
publisher= [http://ssd.jpl.nasa.gov JPL Solar System Dynamics]
url=http://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&body_group=sb&sstr=20000
accessdate=2008-07-02]
abs_magnitude = 3.7cite web
date=2007-11-17 last obs
title=JPL Small-Body Database Browser: 20000 Varuna (2000 WR106)
url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=20000
accessdate=2008-07-02]

20000 Varuna (pron-en|ˈværənə "," ["Merriam Webster's Collegiate Dictionary"] from Sanskrit वरुण IPAlink|vəˈrʊɳə) is a large classical Kuiper Belt object (KBO). It previously had the provisional designation mp|2000 WR|106 and has been precovered in plates dating back to 1953. Under the International Astronomical Union's 2006 draft proposal for the definition of a planet, Varuna would be classified as a dwarf planet if it could be proven to be spherical.

Name

Varuna is named after the Hindu deity Varuṇa. Varuna was one of the most important deities of the ancient Indo-Aryans, and he presided over the waters of the heaven and of the ocean and as the guardian of immortality. [MW Sanskrit-English dictionary] Due to his association with the waters and the ocean, he is often identified with Greek Poseidon and Roman Neptune.

Size

---

thumb|250px|left|Varuna_compared_to_Eris,_Pluto,_Makemake,_Haumea,_Sedna,_Orcus,_Quaoar,_and_Earth.
#Earthrect 646 1714 2142 1994 The Earth
#Eris and Dysnomiacircle 226 412 16 Dysnomiacircle 350 626 197 (136199) Eris
#Pluto and Charoncircle 1252 684 86 Charoncircle 1038 632 188 (134340) Pluto
#Makemakecircle 1786 614 142 (136472) Makemake
#Haumeacircle 2438 616 155 (136108) Haumea
#Sednacircle 342 1305 137 (90377) Sedna
#Orcuscircle 1088 1305 114 (90482) Orcus
#Quaoarcircle 1784 1305 97 (50000) Quaoar
#Varunacircle 2420 1305 58 (20000) Varuna
#link to image (under all other links)rect 0 0 2749 1994

desc none
# - setting this to "bottom-right" will display a (rather large) icon linking to the graphic, if desired

#Notes:
#Details on the new coding for clickable images is here:
#While it may look strange, it's important to keep the codes for a particular system in order. The clickable coding treats the first object created in an area as the one on top.
#Moons should be placed on "top" so that their smaller circles won't disappear "under" their respective primaries.The size of the large KBOs can be determined by simultaneous observations of thermal emission and reflected sunlight. Unfortunately, thermal measures, intrinsically weak for distant objects are further hampered by the absorption of the Earth atmosphere as only the weak ‘tail’ of the emissions is accessible to Earth-based observations. In addition, the estimates are model-dependent with the unknown parameters (e.g. pole orientation and thermal inertia) to be assumed. Consequently, the estimates of the albedo vary resulting in sometimes substantial differences in the inferred size.

Estimates for the size of Varuna have varied from 500 to 1060 km. The two most recent estimates are closer to the 500km range. The 2005 estimate of a size of 936 ±|238|324 km, [http://arxiv.org/abs/astro-ph/0502229 Preprint on arXiv.] ] based on earlier results (900 ±|129|145)cite journal | author=Jewitt D, Aussel H, Evans A | title=The size and albedo of the Kuiper-belt object (20000) Varuna | journal=Nature | volume=411 | issue=6836 | year=2001 | pages=446–7 | doi=10.1038/35078008 PMID 11373669. [http://www.ifa.hawaii.edu/~jewitt/papers/VARUNA/JAE2001.pdf Reprint] on the Author's site.] and (1060 ±|180|-220),cite journal | author=E. Lellouch, R. Moreno, J. L. Ortiz, G. Paubert, A. Doressoundiram and N. Peixinho | title="Coordinated thermal and optical observations of Trans-Neptunian object (20 000)Varuna from Sierra Nevada" | journal=Astronomy & Astrophysics | volume=391 | year=2002 | pages=1133–1139 | doi=10.1051/0004-6361:20020903 [http://www.arxiv.org/abs/astro-ph/0206486 Preprint on arXiv.] ] may be too high.

Orbit

Varuna is classified as a classical trans-Neptunian object and follows a near-circular orbit with a semi-major axis of ~43 AU, similar to that of dp|Quaoar but more inclined. Its orbital period is similar to Quaoar at 283 Earth years.The graph shows the polar view (top; Varuna’s orbit in blue, dp|Pluto’s in red, Neptune in grey). The spheres illustrate the current (April 2006) positions, relative sizes and colours. The perihelia (q), aphelia (Q) and the dates of passage are also marked.Interestingly, the orbits of Varuna and Pluto have similar inclination and are similarly oriented (the nodes of both orbits are quite close).

At 43 AU and on a near-circular orbit, unlike Pluto which is in 2:3 orbital resonance with Neptune, Varuna is free from any significant perturbation from Neptune.The ecliptic view illustrates the comparison of Varuna's near-circular orbit with that of Pluto (highly eccentric, e=0.25), both similarly inclined.

Physical characteristics

Varuna has a rotational period of approximately 3.17 hours (or 6.34 hours, depending on whether the light curve is single or double-peaked). Given the rapid rotation, rare for objects so large, Varuna is thought to be an elongated spheroid (ratio of axis 2:3), with a mean density around 1g/cm³ (roughly the density of water ice).cite journal | url=http://www.iop.org/EJ/article/1538-3881/123/4/2110/201498.html | author=Jewitt D, Sheppard S | title=Physical Properties Of Trans-Neptunian Object (20000) Varuna | journal=Astronomical Journal | volume=123 | issue=April | year=2002 | pages=2110–2120 | doi=10.1086/339557 [http://arxiv.org/abs/astro-ph/0201082 Preprint on arXiv.] ] Examination of Varuna's light curve has found that the best-fit model for Varuna is a triaxial ellipsoid with the axes a,b,c in relations: b/a = 0.63 − 0.80, c/a = 0.45 − 0.52 and a bulk density of 0.992 g/cm³. Since the discovery of Varuna, another, even larger, rapidly rotating (3.9 h) object dp|Haumea has been discovered, also thought to have an elongated shape.D. L. Rabinowitz, K. M. Barkume, M. E. Brown, H. G. Roe, M. Schwartz, S. W. Tourtellotte, C. A. Trujillo (2005), "Photometric Observations Constraining the Size, Shape, and Albedo of mp|2003 EL|61, a Rapidly Rotating, Pluto-Sized Object in the Kuiper Belt", The Astrophysical Journal (2006), 639, Issue 2, pp. 1238-1251 [http://arxiv.org/abs/astro-ph/0509401 Preprint on arXiv] ]

The surface of Varuna is moderately red (similar to dp|Quaoar) and small amounts of water ice have been detected on its surface.cite journal | author=Licandro J, Oliva E, Di Martino M | title=NICS-TNG infrared spectroscopy of trans-neptunian objects 2000 EB173 and 2000 WR106 | journal=Astronomy & Astrophysics | volume=373 | issue=July | year=2001 | pages=29–32L | doi=10.1051/0004-6361:20010758]

References

External links

* Site updated Reretrived on 2006-07-10
* [http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=Varuna;orb=1;view=Far Orbital simulation] from JPL (Java) / [http://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&body_group=sb&sstr=Varuna Ephemeris]