". You may wish to read that first. It explains the meaning of a planet's Orbital Cross; a planet's aphelion, perihelion and its nodes in the ecliptic; as well as other things to consider.
The Orbits of Pluto & Orcus
Although Orcus is a bit smaller than Pluto, Orcus has a nearly identical orbital size, orbital period (year), and orbital inclination. However, Orcus' orbital plane's orientation in our solar system is tilted in the opposite direction from Pluto's. Orcus' orbit clearly reveals Orcus to be a compliment to Pluto. Due to their complimentary relationship, I present them together so we can get a better understanding of their similarities and differences.
inclination to the ecliptic plane.
Pluto and Orcus' perihelions lie north of the ecliptic plane. However, their nodal axes lie
in opposite directions--creating an X in the eciptic with an arc separation of 22° 49'.
The Moons of Pluto & Orcus
Just as Pluto has Charon as its primary moon, so too does Orcus have a moon, discovered on Nov 13, 2005 by M.E. Brown and T.A. Suer. The moon of Orcus, recently named Vanth, was chosen in April 2009. Mike Brown, as the discoverer of Orcus, had the priviledge and was responsible for its naming. In Mike Brown's words as of March 29, 2009:
"The Moon of Orcus has about a ten day orbit around Orcus, in a tight precise circle. We suspect - though can’t yet prove - that Orcus and its satellite have their same faces locked towards each other constantly, like an orbiting dumbbell. Only one other Kuiper belt object and satellite are known to do this. Who? Pluto and Charon, of course.
The origin of the satellite of Orcus is confusing. Pluto and Charon are thought to have formed in a giant collision. Haumea clearly had a shattering blow to disperse moons and other family members. But small Kuiper belt objects are thought to acquired moons by simple capture.
Orcus is right in the middle. Was the satellite from a collision or a capture? We had hoped to answer this question by observations from the Hubble Space Telescope. If the satellite had looked just like other known collisional satellite, we would have been pretty convinced. It doesn’t. Unfortunately that tells us less. We can’t rule out either. We have some ideas of new Hubble Space Telescope observations to try to tell the difference. For now, though, we’re just confused."
Vanth is a daimon (mediator, gatekeeper, demigod) in Etruscan mythology who guides the dead to the underworld.
More on the naming of Orcus's Moon, Vanth, on Mike Brown's blog. (See April 09 entires)
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