astro.wikisort.org - Asteroid

(55637) 2002 UX₂₅ is a trans-Neptunian object that orbits the Sun in the Kuiper belt beyond Neptune. This TNO briefly garnered scientific attention when it was found to have an unexpectedly low density of about 0.82 g/cm³.[12]

(55637) 2002 UX₂₅

2002 UX25 and satellite, as seen by Hubble
Discovery[1]
Discovered by	Spacewatch (291)
Discovery site	Kitt Peak National Obs.
Discovery date	30 October 2002
Designations
MPC designation	(55637) 2002 UX25
Minor planet category	Cubewano (MPC)[2] Extended (DES)[3]
Orbital characteristics[1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 2
Observation arc	25.26 yr (9,228 days)
Earliest precovery date	12 October 1991
Aphelion	48.491 AU
Perihelion	36.485 AU
Semi-major axis	42.488 AU
Eccentricity	0.1413
Orbital period (sidereal)	276.95 yr (101,157 days)
Average orbital speed	4.54 km/s
Mean anomaly	295.71°
Mean motion	0° 0m 12.96s / day
Inclination	19.484°
Longitude of ascending node	204.68°
Time of perihelion	≈ 5 September 2066[4] ±3 days
Argument of perihelion	279.00°
Known satellites	1 (ø: 190–260 km)[5][6]
Physical characteristics
Mean diameter	665±29 km[7] 659±38 km[8]
Mass	(1.25±0.03)×1020 kg[6]
Mean density	0.82±0.11 g/cm3 (assuming equal densities for primary and satellite)[6] 0.80±0.13 g/cm3[8]
Equatorial surface gravity	0.075 m/s2
Equatorial escape velocity	0.227 km/s
Synodic rotation period	14.382±0.001 h[9]
Geometric albedo	0.107+0.005 −0.008[7] 0.1±0.01[8]
Temperature	≈ 43 K
Spectral type	B–V=1.007±0.043[10] V−R=0.540±0.030[10] V−I=1.046±0.034[10]
Apparent magnitude	19.8 [11]
Absolute magnitude (H)	3.87±0.02,[9] 4.0[1]

2002 UX₂₅ has an absolute magnitude of about 4.0,[1] and Spitzer Space Telescope results estimate it to be about 681 km in diameter.[13] The low density of this and many other mid sized TNOs implies that they have likely never compressed into fully solid bodies, let alone differentiated or collapsed into hydrostatic equilibrium, and so are highly unlikely to be dwarf planets.[14]

It was discovered on 30 October 2002, by the Spacewatch program.[15]

Numbering and naming

This minor planet was numbered (55637) by the Minor Planet Center on 16 February 2003 (M.P.C. 47763).[16] As of 2022^[update], it has not been named.[17]

Classification

2002 UX₂₅ has a perihelion of 36.7 AU,[1] which it will next reach in 2065.[1] As of 2020, 2002 UX₂₅ is 40 AU from the Sun.[11]

The Minor Planet Center classifies 2002 UX₂₅ as a cubewano[2] while the Deep Ecliptic Survey (DES) classifies it as scattered-extended.[3] The DES using a 10 My integration (last observation: 2009-10-22) shows it with a minimum perihelion (q_min) distance of 36.3 AU.[3]

It has been observed 212 times with precovery images dating back to 1991.[1]

Physical characteristics

A variability of the visual brightness was detected which could be fit to a period of 14.38 or 16.78 h (depending on a single-peaked or double peaked curve).[18] The light-curve amplitude is ΔM = 0.21±0.06.[9]

The analysis of combined thermal radiometry of 2002 UX₂₅ from measurements by the Spitzer Space Telescope and Herschel Space Telescope indicates an effective diameter of 692 ± 23 km and albedo of 0.107^+0.005
_−0.008. Assuming equal albedos for the primary and secondary it leads to the size estimates of ~664 km and ~190 km, respectively. If the albedo of the secondary is half of that of the primary the estimates become ~640 and ~260 km, respectively.[6] Using an improved thermophysical model slightly different sizes were obtained for UX25 and its satellite: 659 km and 230 km, respectively.[8]

2002 UX₂₅ has red featureless spectrum in the visible and near-infrared but has a negative slope in the K-band, which may indicate the presence of the methanol compounds on the surface.[7] It is redder than Varuna, unlike its neutral-colored "twin" 2002 TX300, in spite of similar brightness and orbital elements.

Composition

With a density of 0.82 g/cm³, assuming that the primary and satellite have the same density, 2002 UX₂₅ is one of the largest known solid objects in the Solar System that is less dense than water.[12] Why this should be is not well understood, because objects of its size in the Kuiper belt often contain a fair amount of rock and are hence pretty dense. To have a similar composition to others large KBOs, it would have to be exceptionally porous, which was believed to be unlikely given the compactability of water ice;[6] this low density thus astonished astronomers.[12] Studies by Grundy et al. suggest that at the low temperatures that prevail beyond Neptune, ice is brittle and can support significant porosity in objects significantly larger than 2002 UX₂₅, particularly if rock is present; the low density could thus be a consequence of this object failing to warm sufficiently during its formation to significantly deform the ice and fill these pore spaces.[19]

Density comparison

What	Density (g/cm3)	Notes
Settled snow	0.2–0.3	[20]
Slush/firn	0.7–0.8	[20]
2002 UX25	0.82	[6]
Glacier ice	0.83–0.92	[20]
Tethys	0.984	[21]
Liquid water	1	[20]

Satellite

The discovery of a minor-planet moon was reported in IAUC 8812 on 22 February 2007.[5] The satellite was detected using the Hubble Space Telescope in August 2005.[5] The satellite was found at 0.16 arcsec from the primary with an apparent magnitude difference of 2.5.[22] It orbits the primary in 8.309±0.0002 days,[9] at a distance of 4770±40 km, yielding a system mass of (1.25±0.03)×10²⁰ kg.[6][9] The eccentricity of the orbit is 0.17±0.03.[9]

This moon is estimated to be 210±30 km in diameter.[7] Assuming the same albedo as the primary, it would have a diameter of 190 km, assuming an albedo of 0.05 (typical of other cold, classical KBOs of similar size) a diameter of 260 km.[6]

References

External links

• MPEC 2002-V08
• Astronomers surprised by large space rock less dense than water, Ron Cowen, Nature, 13 November 2013
• Scientist finds medium sized Kuiper belt object less dense than water, Bob Yirka, Phys.org, 14 November 2013
• (55637) 2002 UX25 at AstDyS-2, Asteroids—Dynamic Site
  • Ephemeris · Observation prediction · Orbital info · Proper elements · Observational info
• (55637) 2002 UX25 at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters

На других языках

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[de] (55637) 2002 UX25

(55637) 2002 UX25 ist ein großes transneptunisches Objekt, das am 30. Oktober 2002 durch das Spacewatch-Programm entdeckt wurde. Mit etwa 665 Kilometern Durchmesser ist (55637) 2002 UX25 eines der größeren Kuipergürtelobjekte und ein potentieller Zwergplanet. 2007 wurde die Entdeckung eines Begleiters bekanntgegeben, der etwa ein Drittel des Durchmessers des Mutterasteroiden aufweist.

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- [en] (55637) 2002 UX25

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[es] (55637) 2002 UX25

(55637) 2002 UX25 es un objeto del cinturón de Kuiper que orbita alrededor del Sol a 42 UA de distancia, descubierto por Spacewatch el 30 de octubre de 2002 desde el Observatorio Nacional de Kitt Peak. Es candidato a la categoría de planeta enano.

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[ru] (55637) 2002 UX25

(55637) 2002 UX25 — очень крупный классический объект пояса Койпера[2]. Оценка размеров позволяет причислить его к кандидатам в карликовые планеты.

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