1. Ch. 12 Dwarf Planets
There are several kinds of objects in our Solar System
Terrestrial planets and Jovian planets, with satellites (moons)
Dwarf planets (which can also have moons) and
“small solar system bodies” – asteroids, comets and meteoroids
Objects are still being classified: Kuiper Belt Objects, Plutoids, Plutinos, Trans-Neptunian Objects (TNOs), Oort cloud objects

2. From largest to smallest, the objects in the Solar System
can be classified
into categories
Notice that there
is some overlap
among objects
of the same size.
FIGURE 9-1 Different Classifications of Solar System Objects
Some of the definitions of the different types of objects in the solar
system overlap. For example, the largest asteroids are also being
classified as dwarf planets; various trans-Neptunian objects
(TNOs) are asteroids or comets; some comets are satellites of
Jupiter; some Kuiper belt objects (KBOs) are satellites of other
KBOs. Furthermore, TNOs exist in two groups: Kuiper belt
objects and Oort comet cloud bodies.

3. The period of Pluto’s orbit is 248 years.
FIGURE 9-4 Orbit of Pluto (a) The high-eccentricity
orbit of dwarf planet (and KBO) Pluto stands out compared
to the orbits of the outer three planets. Notice how
many significant events occurred on Earth during Pluto’s
present orbit of the Sun. (b) Details of Pluto’s passage
inside the orbit of Neptune. The two bodies will never collide.

4. The orbit of Pluto is tilted and elliptical (e = 0.25)
FIGURE 9-4 Orbit of Pluto
(c) A nearly edge-on view of the ecliptic and Pluto’s
orbit compared to it.

7. Kuiper Belt Objects Compared to Moon and Earth
Kuiper Belt Objects Compared to Moon and Earth. Notice that we think Triton was captured by Neptune, and is really an object like Pluto and the KBOs. However, the New Horizons results show that Triton and Pluto are quite different. Also see this web page about KBOs:

8. Eris is a dwarf planet even further than Pluto.
FIGURE 9-9 Dwarf Planet Eris
(a) Orbit of Eris and
Dysnomia compared to the planets and Pluto. Their orbit
around the Sun ranges from 38 to 98 AU, with orbital eccentricity,
e, of 0.44 and orbital inclination of 44o. (b) Keck
Telescope image of dwarf planet Eris and its moon Dysnomia.
(a: Orionist; b: M.E. Brown, W.M. Keck Observatory)

9. Dwarf Planets – five known so far
Dwarf planets are round due to gravity, but not big enough to clear out the other objects in their orbit.
In 2006 three objects—Pluto, Ceres, and Eris—were classified as dwarf planets. Later, we observed Haumea and Makemake, so there are 5 dwarf planets.
Ceres is in the asteroid belt; the other dwarf planets are in the Kuiper Belt out past Neptune .
Many other objects orbit the Sun beyond Neptune. For example, at least 1277 KBO’s have been observed. A few potential Oort cloud objects have also been identified. New classification schemes are being proposed.
Lists are at

10. The orbit of Sedna is huge compared to even
FIGURE 9-20 Sedna’s Orbit (a) The farthest known body in
the solar system is in a highly elliptical orbit (b) that ranges
from the outer reaches of the Kuiper belt and possibly extends
to the inner Oort comet cloud. (NASA/Caltech)
The orbit of Sedna is huge compared to even
the Kuiper belt, and may extend to the Oort cloud.