(55637) 2002 UX25

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Template:Mp (provisional designation Template:Mp) is a trans-Neptunian object that orbits the Sun in the Kuiper belt beyond Neptune. It briefly garnered scientific attention when it was found to have an unexpectedly low density of about 0.82 g/cm3.[1] It was discovered on 30 October 2002, by the Spacewatch program;[2] as of June 2025, the object has yet to be named.

Template:Mp has an absolute magnitude of about 4.0,[3] and Spitzer Space Telescope results estimate it to be about 681 km in diameter.[4] The low density of this and many other mid-sized TNOs implies that they have never compressed into fully solid bodies, let alone differentiated or collapsed into hydrostatic equilibrium, and so are highly unlikely to be dwarf planets.[5]

Numbering and naming

This minor planet was numbered (55637) by the Minor Planet Center on 16 February 2003 (M.P.C. 47763Script error: No such module "Check for unknown parameters".).[6] since 2025Template:Dated maintenance category (articles)Script error: No such module "Check for unknown parameters"., it has not been named.[7]

Classification

File:UX25-LB1-2009Nov19-06UT.jpg
Template:Mp (vmag 19.9) as viewed with a 24" telescope

Template:Mp has a perihelion of 36.7 AU,[3] which it will next reach in 2065.[3] As of 2020, Template:Mp is 40 AU from the Sun.[8]

The Minor Planet Center classifies Template:Mp as a cubewano[9] while the Deep Ecliptic Survey (DES) classifies it as scattered-extended.[10] The DES using a 10 My integration (last observation: 2009-10-22) shows it with a minimum perihelion (qmin) distance of 36.3 AU.[10]

It has been observed 212 times with precovery images dating back to 1991.[3]

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).[11] The light-curve amplitude is ΔM = Script error: No such module "val"..[12]

The analysis of combined thermal radiometry of Template:Mp from measurements by the Spitzer Space Telescope and Herschel Space Telescope indicates an effective diameter of 692 ± 23 km and albedo of 0.107Script error: No such module "Su".. 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.[13] Using an improved thermophysical model slightly different sizes were obtained for UX25 and its satellite: 659 km and 230 km, respectively.[14]

Template:Mp 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.[15] It is redder than Varuna, unlike its neutral-colored "twin" Template:Mpl, 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, Template:Mp is one of the largest known solid objects in the Solar System that is less dense than water.[1] 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;[13] this low density thus astonished astronomers.[1] 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 Template:Mp, 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.[16]

Density comparison
Material Density
(g/cm3) 		Notes
Settled snow 0.2–0.3 [17]
Slush/firn 0.7–0.8 [17]
Template:Mp 0.82 [13]
Glacier ice 0.83–0.92 [17]
Tethys 0.984 [18]
Liquid water 1 [17]

Satellite

File:2002 UX25 moon-orbit.png
A simulated circular orbit of 210-km-diameter moon at a distance of 4770 km

Script error: No such module "infobox".Script error: No such module "Check for unknown parameters". The discovery of a minor-planet moon was reported in IAUC 8812 on 22 February 2007.[19] The satellite was detected using the Hubble Space Telescope in August 2005.[19] The satellite was found at 0.16 arcsec from the primary with an apparent magnitude difference of 2.5.[20] It orbits the primary in Script error: No such module "val". days,[12] at a distance of Script error: No such module "val"., yielding a system mass of Script error: No such module "val"..[13][12] The eccentricity of the orbit is Script error: No such module "val"..[12]

This moon is estimated to be Script error: No such module "val". in diameter.[15] 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.[13]

References

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  1. ↑ a b c Script error: No such module "Citation/CS1".
  2. ↑ Script error: No such module "citation/CS1".
  3. ↑ a b c d Script error: No such module "citation/CS1".
  4. ↑ Script error: No such module "citation/CS1".
  5. ↑ 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 (Template:Mp)', Icarus (forthcoming, available online 30 March 2019) Template:Webarchive DOI: 10.1016/j.icarus.2018.12.037,
  6. ↑ Script error: No such module "citation/CS1".
  7. ↑ Script error: No such module "citation/CS1".
  8. ↑ Script error: No such module "citation/CS1".
  9. ↑ Script error: No such module "citation/CS1".
  10. ↑ a b Script error: No such module "citation/CS1".
  11. ↑ Rousselot, P.; Petit, J.-M.; Poulet, F.; Sergeev, A. Photometric study of Centaur Template:Mp and trans-neptunian object Template:Mp at different phase angles, Icarus, 176, (2005) pp. 478–491.Abstract.
  12. ↑ a b c d Script error: No such module "citation/CS1".
  13. ↑ a b c d e Script error: No such module "Citation/CS1".
  14. ↑ Script error: No such module "Citation/CS1".
  15. ↑ a b Script error: No such module "Citation/CS1".
  16. ↑ Script error: No such module "citation/CS1".
  17. ↑ a b c d Script error: No such module "citation/CS1".
  18. ↑ Roatsch Jaumann et al. 2009, p. 765, Tables 24.1–2
  19. ↑ a b Script error: No such module "citation/CS1".
  20. ↑ Distant EKO The Kuiper Belt Electronic newsletter, March 2007

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External links

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