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. Best available picture of Pluto, prior to 2015,
taken with the Hubble telescope in orbit
FIGURE 9-2 Pluto
This Hubble Space Telescope
image of Pluto shows little detail but indicates that
the major features of Pluto’s surface each cover
large amounts of its area. (Alan Stern, Southwest Research
Institute; Marc Buie, Lowell Observatory; NASA; and ESA)

4. Pluto can barely be resolved by telescopes from Earth
Pluto can barely be resolved by telescopes from Earth. This image of Pluto is from the Hubble telescope.

5. Small objects are discovered by comparing photos taken at different
times or days.
Pluto was
discovered by
this method
in 1930.
FIGURE 9-3 Discovery of Pluto
Pluto was discovered
in 1930 by searching for a dim, starlike
object that slowly moved against the background
stars. These two photographs were taken 1 day
apart. (UC Regents/Lick Observatory)

6. 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.

7. 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.

8. A moon of Pluto was discovered by noticing a bulge in some
photos of Pluto.
FIGURE 9-5 Discovery of Charon
Long ignored as just a defect in the photographic emulsion, the
bump on the upper left side of this image of Pluto
led astronomer James Christy to discover the moon Charon.
(U.S. Naval Observatory)

9. Pluto and its moon Charon are almost like a double planet.
Better photos show two smaller moons: Nix and Hydra.

10. smaller moons: Nix and Hydra.
Better photos show two
smaller moons: Nix and Hydra.
FIGURE 9-6 Pluto’s moons Nix and Hydra
Observations by the Hubble Space Telescope in 2005 revealed two small
moons, each about 5000 times dimmer than Pluto. Named
Nix and Hydra, they are between two and three times farther
from Pluto than is Charon. The lines radiating from Pluto and
Charon are artifacts of the exposure. (NASA)

11. Websites: http://pluto.jhuapl.edu/
The New Horizons spacecraft flew by Pluto in July 2015 and greatly increased our knowledge of this dwarf planet.
Websites:
FIGURE 9-7 Pluto and Charon
This picture of Pluto and its moon, Charon, is a composite of Hubble
Space Telescope images. It shows the greatest detail
we have of Pluto’s surface. Pluto and Charon are separated
here by only 19,700 km. Inset: A map covering 85% of Pluto’s
surface. The contrast between dark and light strongly suggests
regions covered with ice and regions covered with rocky material.
(Pluto: Alan Stern/SwRI, Mar Cuie/Lowell Observatory, NASA, &
ESA; Charon: R. Albrecht, ESA/ESO Space Telescope European
Coordinating Facility, and NASA; inset: A. Stern/SwRI, M. Buie/Lowell
Observatories, NASA, and ESA)

18. Pluto images, best seen in a web browser:
Methane snow on peaks
High resolution pictures of Sputnik Planum, an ocean of solid nitrogen
Mountains and plains, with haze layers
geology map with color to denote different types of surface
New Horizons trajectory
For class, we downloaded 3 videos and saved them to the classroom PC.

19. The Pluto–Charon Orbit is so unusual that it probably means Charon is captured, and not co-evolved with Pluto

20. 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:

21. Ultima Thule – a Kuiper Belt Object past Pluto
The Kuiper Belt is a “third zone” of the Solar system:
After the Pluto flyby, New Horizons was directed toward a small KBO initially called 2014MU69; the trajectory is shown at
Now called Ultima Thule, this KBO has a completely unexpected shape, like a snowman:

22. 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)

23. Keck telescope image of Eris and its moon Dysnomia.
FIGURE 9-9 Dwarf Planet Eris
(b) Keck Telescope image of dwarf planet Eris and its moon Dysnomia.
(a: Orionist; b: M.E. Brown, W.M. Keck Observatory)
Keck telescope image of Eris and its moon Dysnomia.

24. 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

25. 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.
This object has not yet been classified.