I. Uranus and Neptune: Discoveries, atmospheres, interiors, rotation, magnetic fields, moons, rings, Uranus’ axis tilt and seasons.

II. Pluto and Charon: Orbit, composition, other moons, why so different from Jovian planets?

III. Transneptunian Bodies (the Kuiper belt)

Outline of Uranus, Neptune and Pluto (Ch. 8 part II and Ch 9 part I Not exactly like Book)

Planet Distance(AU)

Mass(Earth = 1)

Moons Density(Water =1)

Mercury 0.39 0.05 0 5.43Venus 0.72 0.9 0 5.25Earth 1.0 1.0 1 5.52Mars 1.5 0.11 2 3.95Jupiter 5.2 318 28 1.33Saturn 9.5 95 18 0.69Uranus 19.2 17 21 1.29Neptune 30.1 17 8 1.64Pluto 39.5 0.002 3 2.03

Not known to ancient greeks, discovery details.

Composition : H, He, CH4, NH3, etc. Atmospheres: less active, dark spot on

Neptune Interior: liquid hydrogen but no metallic

hydrogen Rotation: fast (~17 hours for both) Magnetic field: strong (but not know how it

is produced) Moons: many moons, Neptune’s Triton is

larger than Pluto and retrograde (probably captured)

Rings: dark and faint, Neptune has incomplete ring arcs

Uranus and Neptune

Interiors of Jovian Planets

Interiors

If Uranus is at its Autumnal Equinox, what does that mean?

Question 1

If Uranus it is at its Autumnal Equinox, what does that mean?

a) Nothing, Uranus has no seasonsb) The Sun is crossing Uranus’ equator

from North to Southc) The Sun is at its northernmost point

on Uranus d) The Sun is in the southern

hemisphere of Uranus

Question 1

If Uranus it is at its Autumnal Equinox, what does that mean?

a) Nothing, Uranus has no seasonsb) The Sun is crossing Uranus’

equator from North to Southc) The Sun is at its northernmost point

on Uranus d) The Sun is in the southern

hemisphere of Uranus

Question 1

Uranus takes 84 years to orbit the Sun. In 2007 Autumn started in the northern hemisphere of Uranus, when will Winter start in the northern hemisphere of Uranus? a) 84 years laterb) 42 years laterc) 21 years laterd) In 2008

Question 2

Uranus takes 84 years to orbit the Sun. In 2007 Autumn started in the northern hemisphere of Uranus, when will Winter start in the northern hemisphere of Uranus? a) 84 years laterb) 42 years laterc) 21 years later in 2028d) In 2008

Question 2

Triton: largest of Neptune’s moons

Larger than Pluto

and in a retrograde

orbit

Triton: largest of Neptune’s moons Larger

than Pluto and in a

retrograde orbit

Why does a retrograde

orbit indicate capture?

II. Pluto and Charon: Orbit, composition, other moons (Nix & Hydra), why so different from Jovian planets?

Outline of Uranus, Neptune and Pluto

Pluto and Charon

Discovery of Caron with ground based telescope

Hubble Space Telescope

Pluto and its three Moons

Planet Distance(AU)

Mass(Earth = 1)

Moons Density(Water =1)

Mercury 0.39 0.05 0 5.43Venus 0.72 0.9 0 5.25Earth 1.0 1.0 1 5.52Mars 1.5 0.11 2 3.95Jupiter 5.2 318 28 1.33Saturn 9.5 95 18 0.69Uranus 19.2 17 21 1.29Neptune 30.1 17 8 1.64Pluto 39.5 0.002 3 2.03

Solar Nebula was “thinning

out hence U and N are smaller than J and S

and so is Pluto and its trans-

neptunian relatives

III. Transneptunian Bodies (the Kuiper belt):

Many objects smaller than planets: similar to the asteroid belt

Largest object (Eris) is slightly larger than Pluto

Source of some of the comets Triton may have formed in the

Kuiper belt was captured by Neptune (Triton’s orbit is retrograde)

Outline of Uranus, Neptune and Pluto (Ch. 8 part II and Ch 9 part I )

Would you expect the composition of objects in the Kuiper belt to be? a) The same as those in the asteroid beltb) Iron cores and silicate mantlesc) Hydrogen and heliumd) None of the above

Question 3

Would you expect the composition of objects in the Kuiper belt to be? a) The same as those in the asteroid beltb) Iron cores and silicate mantlesc) Hydrogen and heliumd) None of the above

Question 3

Kuiper Belt

•

~50 AU

Sun

Neptune’s Orbit

Outer Solar System

Outer Solar System

Collision in the Kuiper BeltPaiting by Daniel D. Durda

Is Pluto a planet or a Kuiper Belt object?

Is Pluto a planet or a Kuiper Belt object? Pluto is well beyond Neptune, in the

Kuiper Belt. Inclined orbit is typical of Kuiper Belt

objects. Composition is typical of Kuiper Belt

objects, but not like any of the other planets.

Is Pluto a planet or a Kuiper Belt comet? One Kuiper Belt object has been found that is

slightly larger Pluto’s size (Eris, a.k.a. object 2003 UB313) and several slightly smaller.

Kuiper Belt objects have similar orbital resonances with Neptune.

Kuiper Belt objects can have moons. Triton (a captured moon of Neptune) is even

larger than Pluto.

What have we learned?• What is Pluto like?Pluto is much smaller than

any other planet, with an orbit more elliptical and more inclined to the ecliptic plane than that of any other planet. It is made mostly of ices and has a very thin atmosphere of gases that are expected to freeze onto the surface as Pluto moves farther from the Sun in its 248-year orbit. It has a moons.

• Is Pluto a planet or a Kuiper belt object?

Pluto was called a planet by the International Astronomical Union until 2006. Its properties suggest that it is one of the largest members of the Kuiper belt objects. Its composition and orbital properties match those of other Kuiper belt objects and do not fit in with the other planets. It was the largest known Kuiper belt object until summer 2005 now there is a larger one further out.