“Ura

nus

& N

eptu

ne, T

he Ic

e G

iant

s”

Wha

t We

Will

Lea

rn T

oday

•H

ow &

Whe

n w

ere

Ura

nus

& N

eptu

ne

disc

over

ed?

•H

ow a

re th

e in

terio

rs a

nd w

eath

er o

n th

ese

plan

ets?

•W

hy is

Nep

tune

as

“war

m”

as U

ranu

s?•

Wha

t are

thei

r m

oons

and

rin

gs li

ke?

•W

hat i

s sp

ecia

l abo

ut T

riton

, Nep

tune

’s

moo

n?•

How

are

thes

e w

orld

s un

ique

in th

e S

S?

Pro

pert

yU

ranu

sN

eptu

ne

Sem

i-maj

orax

is19

.2 A

U30

.1 A

U

Siz

e (r

adiu

s)4.

0 R

Ear

th3.

9 R

Ear

th

Mas

s14

.5 M

Ear

th17

.1 M

Ear

th

Ave

rage

den

sity

1.32

g/c

c1.

64 g

/cc

Com

posi

tion

H, H

e, H

-com

poun

dsH

, He,

H-c

ompo

unds

Clo

ud-t

op T

emp

60K

60 K

Moo

ns>

27

> 1

3

Orb

italp

erio

d84

year

s16

5 ye

ars

Rot

atio

n pe

riod

*-1

7.3

hour

s16

hou

rs

Axi

s til

t97

.9o

29.6

o

Orb

ital i

nclin

atio

n0.

77o

1.77

o

Orb

ital e

ccen

tric

ity0.

046

0.01

0

Pla

net D

etai

ls

Ret

rogr

ade

Mos

t ext

rem

e

As

“war

m”

as U

ranu

s!

* M

easu

red

base

d on

rot

atio

n of

mag

netic

fiel

d lin

es

Sm

alle

st J

ovia

n

Ura

nus

& N

eptu

ne’s

Dis

cove

ry•

Firs

t pla

nets

dis

cove

red

usin

g a

tele

scop

e•

Ura

nus

disc

over

ed in

178

1 by

Will

iam

&

Car

olin

e H

ersc

hel

–A

lthou

gh fa

intly

vis

ible

to n

aked

-eye

, doe

s no

t “w

ande

r” a

s m

uch

due

to it

s lo

ng 8

4 ye

ar o

rbit

–D

isco

vere

d du

ring

a su

rvey

of t

he s

kies

•C

aref

ul o

bser

vatio

ns o

f Ura

nus

show

s de

viat

ion

in p

ath

vs. N

ewto

n’s

law

s•

Ada

ms

& L

ever

rier

inde

pend

ently

pre

dict

ed

influ

ence

on

Ura

nus

from

an

unse

en e

ight

h pl

anet

•N

eptu

ne d

isco

vere

d in

184

6 by

Gal

le b

ased

on

Leve

rrie

r’spr

edic

tion

of it

s po

sitio

n!

For

mat

ion

of U

ranu

s &

Nep

tune

•S

imila

r to

Jup

iter

and

Sat

urn,

cor

e of

abo

ut 1

0 M

Ear

thfo

rmed

from

hyd

roge

n co

mpo

unds

•A

ccre

ted

muc

h sm

alle

r at

mos

pher

e–

Orb

it ar

ound

the

Sun

is m

uch

bigg

er–

Acc

retio

n sl

ower

as

a re

sult

–S

olar

win

d bl

ew a

way

gas

into

inte

rste

llar

spac

e–

Sto

pped

pla

net f

orm

atio

n, le

avin

g U

ranu

s an

d N

eptu

ne le

ss m

assi

ve

Inte

rior

of U

ranu

s &

Nep

tune

Fig

11.

5

•N

o liq

uid

or m

etal

lic h

ydro

gen

–N

ot e

noug

h pr

essu

re

•R

ock

& m

etal

cor

e–

Larg

er th

an J

upite

r &

Sat

urn

as it

is n

ot w

eigh

ed d

own

by a

larg

e at

mos

pher

e

•H

ydro

gen

com

poun

d la

yer

–D

iffer

entia

ted

over

roc

k &

met

al c

ore

unlik

e Ju

pite

r &

Sat

urn

•G

aseo

us h

ydro

gen

•V

isib

le c

loud

s•

Ura

nus

–C

oole

d of

f and

dul

l (as

exp

ecte

d)

•N

eptu

ne–

Inte

rnal

hea

t sou

rce!

–P

erha

ps d

ue to

ong

oing

con

trac

tion

•Li

ke w

hich

oth

er p

lane

t?

Atm

osph

ere

& W

eath

er•

~ 8

4% H

, 14%

He,

2%

CH

4

•M

etha

ne c

onde

nses

into

“s

now

flak

es”

less

than

100

km

bel

ow th

e cl

oud

tops

–G

ives

the

blue

col

or

–M

etha

ne g

as a

bove

abs

orbs

re

d lig

ht

–M

etha

ne c

loud

s re

flect

blu

e lig

ht

•W

hy is

Nep

tune

blu

er?

–U

ranu

s ha

s sm

og-li

ke la

yer

due

to it

s ex

trem

e se

ason

s

–S

catte

rs b

lue

light

bef

ore

reac

hing

clo

uds

Fig

11.

7

Win

ds &

Wea

ther

•U

ranu

s–

Voy

ager

2 s

aw n

o ba

nds

or c

loud

s in

19

86–

Sub

sequ

ent H

ST

and

AO

obs

erva

tions

re

veal

sto

rms

brew

ing

–P

erha

ps d

ue to

cha

ngin

g se

ason

s N

H

seei

ng S

unlig

ht a

fter

42 y

ears

!

•N

eptu

ne–

Ban

ded

atm

osph

ere

with

sto

rms

and

clou

ds–

Gre

at D

ark

Spo

t •

Last

ed o

nly

abou

t 6 y

ears

Fig

11.

11 c

, Kec

k IR

imag

e

Fig

11.

11 d

Mag

netic

Fie

lds

•M

oder

ate

size

d m

agne

tosp

here

des

pite

wea

k fie

ld–

Liqu

id c

ore

of m

etal

s an

d hy

drog

en c

ompo

unds

gen

erat

e m

agne

tic fi

eld

–W

eake

r sol

ar w

ind

pres

sure

al

low

s m

oder

ate

size

d m

agne

tosp

here

•B

oth

mag

netic

axe

s ar

e ve

ry

tilte

d w

ith r

espe

ct to

rot

atio

n ax

es–

Don

’t kn

ow w

hy

Fig

11.

13

Ura

nus’

Med

ium

Siz

ed M

oons

•A

ll na

med

afte

r S

hake

spea

re's

cha

ract

ers

•M

ade

mai

nly

of ic

es (

wat

er, m

etha

ne, a

mm

onia

)•

Voy

ager

flyb

y ga

ve u

s in

form

atio

n an

d ra

ised

qu

estio

ns–

Arie

l & U

mbr

iela

re v

irtua

l tw

ins,

but

onl

y A

riel s

how

s ev

iden

ce o

f vol

cani

sm &

tect

onic

s–

Tita

nia

& O

bero

n ar

e al

so s

imila

r si

ze, b

ut o

nly

Tita

nia

show

s ge

olog

ical

act

ivity

•M

irand

a, th

e sm

alle

st,

show

s

man

y te

cton

ic fe

atur

es a

nd

rela

tivel

y fe

w c

rate

rs–

Per

haps

due

to p

ast t

idal

hea

ting

Fig

11.

28

Nep

tune

’s C

aptu

red

Moo

ns•

Man

y re

trog

rade

orb

its, h

igh

incl

inat

ions

–C

aptu

red

aste

roid

s

•T

riton

is th

e la

rges

t cap

ture

d ob

ject

in th

e S

olar

S

yste

m–

Col

dest

wor

ld in

the

sola

r sy

stem

(hi

gh a

lbed

o)–

Onc

e or

bite

d th

e S

un

as a

KB

O–

Larg

er th

an P

luto

–R

etro

grad

e or

bit

–S

pira

ling

into

Nep

tune

–W

ill c

ross

Roc

he L

imit

in

abou

t 100

mill

ion

year

s–

Evi

denc

e of

pas

t geo

logi

cal a

ctiv

ity•

Pas

t ecc

entr

ic o

rbit

caus

ed ti

dal h

eatin

g

Fig

11.

29

Rin

gs

•U

ranu

s’ r

ings

are

tipp

ed

over

–P

hoto

from

HS

T in

IR

•N

eptu

ne r

ings

pic

ture

was

ta

ken

by V

oyag

er

Fig

11.

34

Uni

que

Fea

ture

s of

Ura

nus

•F

irst S

S p

lane

t to

be d

isco

vere

d w

ith a

tele

scop

e–

Far

thes

t nak

ed e

ye p

lane

t, bu

t not

rec

ogni

zed

as a

pl

anet

•T

he m

ost t

ilted

pla

net

–M

oon

and

rings

are

like

bul

ls-e

ye f

rom

the

Sun

/Ear

th–

Mos

t ext

rem

e se

ason

s–

42 y

ears

of d

ay a

nd 4

2 ye

ars

of n

ight

!

•T

he o

nly

gas

gian

t to

have

no

inte

rnal

hea

t so

urce

Uni

que

Fea

ture

s of

Nep

tune

•A

s w

arm

as

Ura

nus

desp

ite g

reat

er d

ista

nce

from

the

Sun

–In

tern

al h

eat s

ourc

e

•La

rges

t cap

ture

d m

oon

–R

etro

grad

e or

bit

•M

any

moo

ns w

ith w

acky

orb

its–

Cap

ture

d K

BO

s

•T

riton

is c

olde

st w

orld

in th

e S

olar

Sys

tem

–35

K, -

238

o C, -

396

o F

•S

mal

lest

gas

gia

nt p

lane

t

Voy

ager

Mov

ies