TNOs – KBOs - EKOs The “tenth” planet? 90337 Sedna • e: 0.849 • a: 502.040 AU • q: 76.032 AU • Q: 928.048 AU • P: 11249.05 yr • i: 11.932°
Estimated diameter: 1180-1800 km. At the time of its discovery it was the largest object in the solar system since Pluto. It is now 5th? largest known TNO after 2003 UB313, Pluto, 2005 FY9, and 2003 EL61. Sedna is one of the reddest objects in the solar system, nearly as red as Mars: possibly caused by a hydrocarbon sludge, or tholins on its surface. Sedna was argued to be the first observed Oort cloud body, and was described as being an inner Oort cloud object, situated in the disc reaching from the Kuiper belt to the spherical part of the cloud. Kenyon and Bromley
76 2004 showed rather that it is probably a KBO jarred loose by a passing star, but the book is far from closed.
• About 1630 KBOs (2013) The “tenth” planet? Eris have been observed (more with uncertain orbits) • Many cluster in mean- e: 0.4378 motion resonances with a: 67.89 AU Neptune (resonant KBOs) q: 38.2 AU • Those in 3:2 resonance Q: 97.610 AU with Neptune are called Neptune crossing line Plutinos (Pluto is also in i: 43.993° this resonance); those in P: 557 yr 2:1, twotinos (ugh!) • Those that have been scattered onto larger orbits by Neptune have q~30 AU (near Neptune) are the scattered disk or SKBOs • CKBOs or the classical • Eris (2003 UB313) has a diameter of 2,700 km, and is about Kuiper belt are the 25% more massive than Pluto (some debate). Initial remainder, sometimes observations show that methane ice is present on the object's called cubewanos after surface. This makes 2003 UB313 more similar to Pluto than 1992 QB1, the first KBO previously discovered large outer solar system planetoids. discovered
Duncan Levison Budd (1995) numerical survey
• Pluto, Eris and Haumea all have moons(!)
Stability map @ i=0
1 Kuiper belt properties
• Assuming albedos of 4% (similar to comets),Haumea this means most KBOs seen so far are 25-150 km (larger than most comets) with some up to Pluto size (hence the discussion of Pluto as planet vs KBO) • Note: recent Spitzer observations point to higher (18%) albedos, which would make the objects smaller! 5 • Observations extrapolated indicatedMakemake ~10 objj,ects > 25 km, total mass 0.2 MEarth in the range 30AU < r < 50 AU • Gray to reddish colours (like comet nuclei)
Estimated Eris number of Pluto- sized dwarf planets in the Kuiper Belt ~100
So which ones of these should be called planets? Pluto and Charon • Pluto may well be the “largest” of the KBOs (2270 km diameter) • However, it and its large moon Charon have high albedos (~.6 Pluto an Charon from HST and4d ~.4 resp. ) • Density ~ 2g/cm3 • Tenuous atmosphere, Three small N2 and CO, which may satelltes of Pluto, only exist when near Hydra and Nix perihelion ? and the most recently discovered (in 83 2011) temporarily called P4
Why isn’t Pluto a planet anymore? • Pluto is not a planet because it has not cleared everything from its orbit. The criteria to be a planet are: – It orbits the Sun – It is large enough for gravity to squash it into a ball – It must have cleared everything in its orbit (Pluto did not fulfill this). • Those objects which can satisfy the first two but not the third are now called “dwarf planets” 84
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