Dwarf Planet 136108 Haumea reaches oposition.

The Dwarf Planet 136108 Haumea will reach opposition (i.e. be directly opposite the Sun seen from Earth) at 8.38 pm GMT on Sunday 21 April 2024. This means that it will both be at its closest to the Earth this year, about 49.10 AU (19.28 times the average distance between the Earth and the Sun, or about 7 345 255 000 km), and completely illuminated by the Sun. While it is not visible to the naked eye observer, the planets have phases just like those of the Moon; being further from the Sun than the Earth, 136108 Haumea is 'full' when directly opposite the Sun. The Dwarf Planet will be in the constellation of Bootes and at its highest point in the sky at about midnight local time from anywhere on Earth (this is because the rising and setting of objects in the sky is caused by the Earth's rotation, not the movement of the object). (Even at it's very brightest 136108 Haumea will only have a Magnitude of 17.3, making it almost impossible to see with any but the largest of Earth-based telescopes, and where resolvable it will only be possible to see it as a point of light indistinguishable from a faint star.

The orbit and position of 136108 Haumea at 9.00 pm on Sunday 21 April 2024. JPL Small Body Database Browser.

136108 Haumea orbits the Sun on an eccentric orbit tilted at an angle of 28.2° to the plane of the Solar System, which takes it from 34.4 AU from the Sun (34.4 times the average distance at which the Earth orbits the Sun) to 51.5 AU from the Sun (51.5 times the average distance at which the Earth orbits the Sun). With an average distance of 43.0 AU, 136108 Haumea completes one orbit around the Sun every 282 years. This means that the planet is almost stationary compared to the faster moving Earth, so that it reaches Opposition only one day later each year than the year before, and reaches Solar Conjunction (when it is directly on the opposite side of the Sun to the Earth), roughly six months later.

The Dwarf Planet Haumea is believed to rotate in just under 4 hours. This rapid rotation causes the Dwarf Planet to be elongated in appearance. Stephanie Hoover/Wikimedia Commons.

136108 Haumea was discovered on 28 December 2004 by a team led by Mike Brown of the Palomar Observatory in California, in images taken by them on 28 May 2004; on 27 July 2005 a team led by José Luis Ortiz Moreno and his team at the Instituto de Astrofísica de Andalucía reported that they had also discovered the Dwarf Planet, in images taken between 7 and 10 March 2003. With a diameter of 2100 km it is considered to be the third largest dwarf planet in the Solar System (after 134340 Pluto and 136199 Eris) as well as the eighteenth largest body in the Solar System, excluding the Sun (several moons, including our own, are larger).

Haumea has been calculated to be rotating once every 3.9 hours, far more rapidly than any other large body in the Solar System. Curiously for such a fast rotating body, it has not adopted a oblate spheroid (flattened sphere) shape, but is instead a triaxial ellipsoid (elongate flattened sphere, or flattened egg-shape). This implies that, although its surface is comprised of ice, it has a core of fairly dense rocky material. The Dwarf Planet also appears to be surrounded by a ring of icy material, and at least two moons, which have been named Hiʻiaka and Namaka.

Dwarf Planet Haumea and its satellites, imaged by the Hubble Space Telescope's WFC2 camera from 12 May 2008 and 19 May 2008. The brighter dot orbiting Haumea is the larger outer moon Hi'iaka while the fainter dot is the smaller inner moon Namaka. This animation of the moons' orbits spans 7 days and the orbital plane of Namaka is oriented vertically. Hubble Space Telescope/Michael Brown/Wikimedia Commons.

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The shape of Kuiper Belt Object 2003 SQ317.

The Kuiper Belt is a region of the Solar System extending from the orbit of Neptune at about 30 AU (i.e. 30 times the distance between the Sun and the Earth) out to about 50 AU from the Sun it contains a very large number of bodies known as Kuiper Belt Objects, which are thought to be left over from the formation of the Solar System, elements of the original proto-planetary disk that were to widely scattered, and had to high an angular momentum, to assemble into planets under their own gravity. Some of these objects are large enough to be considered dwarf planets, notably Pluto (formerly considered to be a planet), Makemake and Haumea.

In a paper published on the online arXiv Database at Cornell University Library on 6 September 2013,  and in the Monthly Notices of the Royal Astronomical Society on 3 December 2013, Pedro Lancerda and Andrew McNeill of the Astrophysics Research Centre at Queen's University Belfast and Nuno Peixinho of the Center for Geophysics and Geophysical and Astronomical Observatory of the University of Coimbra, describe attempts to model the shape of one particular Kuiper Belt Object 2003 SQ317.

2003 SQ317 was discovered in September 2003 (the designation 2003 SQ371 indicates that it was the 7941st object discovered in the second half of September 2003). It has an eccentric 279 year orbit inclined to the plane of the Solar System, with an average distance of 42.7 AU from the Sun. It is considered to be a Haumea Family Object, a body with a similar orbital path and albedo to the dwarf planet Haumea, possibly formed by an ancient collision involving the proto-Haumea and another body, though modeling a scenario that could start in such a collision and end with the current pathways of these objects has proved elusive. In 2010 it was noted that 2003 SQ317 had a notably variable albedo, dimming and brightening by a factor of 14 over a period of 3.7 hours, suggesting that it might have a highly irregular shape.  

The calculated orbit of 2003 SQ317. JPL Small Body Database Browser.

Based upon additional observations of 2003 SQ317 using the ESO New Technology Telescope located at the La Silla Observatory in Chile, Lancerda et al. attempted to build a model of the object that fit with the observed pattern of brightening and darkening. 

They were able to come up with two, equally plausible models to account for this. Firstly 2003 SQ317 could be an flattened elongate body (Jacobi ellipsoid) spinning so that the body alternatively presents long and short sides to the Earth. Secondly the object could in fact be a pair of gravitationally bound bodies (a Roche binary pair), rotating one in front of the other, so that alternately one and two bodies can be seen.

Jacobi ellipsoid model that best fi ts the lightcurve of 2003 SQ317. Lancerda et al. (2013).

Roche binary model that best fi ts the lightcurve of 2003 SQ317. Lancerda et al. (2013).

2003 SQ317 is too small and too distant for its shape to be resolved visually with any current telescope. It would in theory be possible to differentiate between the two models it the mass of the object were known (the binary pair would need to be considerably more dense than the Jacobi ellipsoid), though there is no easy way to do this at the current time. 2003 SQ317 is likely to be a rubble pile type object rather than one or two large rocks, which would allow it quite a range of possible densities, and make it hard to determine its density based upon its mineralogy (which can sometimes be assessed from albedo).

See also Asteroids in retrograde orbits, Four more asteroids found to be co-orbitals of Neptune, Neptune's Trailing Trojans, The stability of Neptune's Trojan Asteroids and Pluto gains a fourth moon.

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