Post on 25-Jun-2020
Planets & Life
Planets & Life
PHYS 214
PHYS 214
Dr Rob Thacker
Dr Rob Thacker
Dept of Physics (308A)
Dept of Physics (308A)
thacker@
astro.queensu.ca
thacker@
astro.queensu.ca
Please start all class related emails with
Please start all class related emails with ““214:
214:””
Midterm
details
Midterm
details
��Walter Light Hall
Walter Light Hall Rm
Rm
205 9:30
205 9:30 ––
10:30 (so
10:30 (so
within our usual class slot)
within our usual class slot)
��Half multiple choice, half short answ
erHalf multiple choice, half short answ
er
��On the material in weeks 1
On the material in weeks 1-- 55
��On conflicts:
On conflicts:
��““If a conflict arises with one course scheduling their
If a conflict arises with one course scheduling their
exam
outside of their usual slot, then it is the
exam
outside of their usual slot, then it is the
responsibility of the instructor scheduling outside of
responsibility of the instructor scheduling outside of
the slot to m
ake accommodations for students
the slot to m
ake accommodations for students
unable to attend due to a conflict
unable to attend due to a conflict ””
Homework
Homework
��If you haven
If you haven’’ t already handed in assignment 1
t already handed in assignment 1
please do so at the end of class
please do so at the end of class
��Assignment 2 will be posted this afternoon
Assignment 2 will be posted this afternoon
��Questions on stars, radiation from stars & habitable
Questions on stars, radiation from stars & habitable
zones
zones
Rem
embe
r: no lectur
e Frida
y
Today
Today’’ s Lecture
s Lecture
��The
The Jovian
Jovian
planets
planets
��Brief discussion of the space
Brief discussion of the space --craft we have sent to these
craft we have sent to these
planets
planets
��Physical characteristics of the
Physical characteristics of the Jovian
Jovian
planets
planets
��Possibility of life?
Possibility of life?
We ar
en’t going
to the star
s soon
. If w
e wan
t to loo
k for life
on othe
r plan
ets,
then
our
own solar system
is the on
ly place w
e can send
probe
s.
Goo
gle vide
o ha
s copies of “V
oyag
e to the
Plane
ts”a fact bas
ed but ficitiona
laccoun
t
of the
possibilit
y of hum
ans trav
ellin
gto all
the plan
ets.
Definitely worth a w
atch.
Mass distribution in the solar system
Mass distribution in the solar system
0.0000001%
?0.0000001%
?Interplanetary medium
Interplanetary medium
0.0000001%
?0.0000001%
?Meteroids
Meteroids
0.0000002%
?0.0000002%
?Minor planets
Minor planets
0.00005%
0.00005%
Satellites (moons)
Satellites (moons)
0.01%
0.01%
Comets
Comets
0.135%
0.135%
Planets
Planets
99.85%
99.85%
Sun
Sun
Contribution
Contribution
Object
Object
Jupiter is m
ore than
twice as
mas
sive as the rest of the plan
etscombine
d.
Comparison: Orbital data
Comparison: Orbital data
��Orbit R: Period P: Mass M:
Orbit R: Period P: Mass M:
(in AU) (in years) (
(in AU) (in years) ( ��
Earth)
Earth)
��Jupiter 5.2
Jupiter 5.2
1212318
318
��Saturn
Saturn
9.6
9.6
30309494
��Uranus
Uranus
19.2
19.2
85851515
��Neptune 30.1
Neptune 30.1
165
165
1717
Nep
tune gets 1/3
02=1/9
00th
of th
e radiation that the
Earth
gets
Voyagers 1 & 2
Voyagers 1 & 2
��Unmanned probes sent to O
uter solar system
Unmanned probes sent to O
uter solar system
(launched 1977)
(launched 1977)
��Voyager 1 visited Jupiter & Saturn
Voyager 1 visited Jupiter & Saturn
��Voyager 2 visited Jupiter, Saturn, U
ranus,
Voyager 2 visited Jupiter, Saturn, U
ranus,
Neptune
Neptune
��Each probe carries a `G
olden Record
Each probe carries a `G
olden Record’’
containing inform
ation about the Earth
containing inform
ation about the Earth
��Also includes cartridge and needle needed to m
ake a
Also includes cartridge and needle needed to m
ake a
player for the record
player for the record
Voyager trajectories
Voyager trajectories
Although lau
nch
ed a
2 w
eeks after Voyag
er 2
Voyag
er 1 rea
ched
Jupiter
first
Voyag
er 2 use
d a slingsh
ot
from S
aturn
to pro
pel it
on toward U
ranus & N
eptune
(took 12 yea
rs to rea
ch N
eptune!)
The Golden Record
The Golden Record
��Content decided upon by a
Content decided upon by a
committee headed by Dr
committee headed by Dr
Carl
Carl Sagan
Sagan
��115 images, followed by
115 images, followed by
greetings in 56 languages, a
greetings in 56 languages, a
series of sounds of Earth
series of sounds of Earth
and then 90 minutes of
and then 90 minutes of
music
music
��Sounds include
Sounds include
��Dog
Dog……
��Chimp
Chimp……
Voyag
ers still tak
e 40,0
00 yea
rs to trav
el 1
.6 light yea
rs! U
nbelieva
bly un
likely to be pick
ed up!
Galileo
Galileo
(Jupiter)
(Jupiter)
��More recent spacecraft (launched 1989) which orbited
More recent spacecraft (launched 1989) which orbited
around Jupiter until 2003
around Jupiter until 2003
��It was destroyed to prevent the possible contamination of the
It was destroyed to prevent the possible contamination of the
Europa
Europa , one of Jupiter
, one of Jupiter’’ s m
oons that
s moons that harbours
harboursliquid water
liquid water
under an ice surface
under an ice surface
��Deployed probe into Jupiter
Deployed probe into Jupiter’’ s atm
osphere
s atmosphere
Even with a dam
aged
antenna it has relayed
back some im
portant
data and beautiful
pictures (right: Jupiter’s
rings)
Cassini
Cassini --Huygens
Huygens
(Saturn)
(Saturn)
��Collaboration between N
ASA and European
Collaboration between N
ASA and European
Space agency (ESA)
Space agency (ESA)
��NASA built the
NASA built the Cassini
Cassiniorbiter
orbiter
��ESA built the
ESA built the Huygen
Huygen’’ sslander
lander
(landed on Titan)
(landed on Titan)
��Launched in 1997, took 4 gravity assists to get it
Launched in 1997, took 4 gravity assists to get it
to Saturn
to Saturn
��Also included the heaviest payload of plutonium
Also included the heaviest payload of plutonium
ever launched in a rocket (36.5 kg!)
ever launched in a rocket (36.5 kg!)
A few thoughts about interplanetary
A few thoughts about interplanetary
exploration
exploration ––is it expensive?
is it expensive?
��Cost of Galileo m
ission ~ $1.5 billion (over 10
Cost of Galileo m
ission ~ $1.5 billion (over 10
years)
years)
��Cost of
Cost of Cassini
Cassini --Huygens mission = $3.26 billion
Huygens mission = $3.26 billion
(over a similar period)
(over a similar period)
��US annual G
DP ~ $10 trillion
US annual G
DP ~ $10 trillion
��US defense budget around $400 billion
US defense budget around $400 billion
��NASA Budget per year around $16 billion
NASA Budget per year around $16 billion
��Cost of entire Apollo project ~ $150 billion in
Cost of entire Apollo project ~ $150 billion in
today
today’’ s dollars
s dollars
You
decide…
Jupiter
Jupiter
Very strong banding
of clouds
in equatorial
region
(Pictu
re fro
m the
Cas
sini`M
illeniu
mfly-b
y’)
Great R
ed S
pot
Jupiter Facts
Jupiter Facts
��Diameter: 142,000 km (11
Diameter: 142,000 km (11��
Earth)
Earth)
��Rotation period is
Rotation period is a
bout
abou
t9.8 hours (very fast)
9.8 hours (very fast)
��Different latitudes rotate at different rates
Different latitudes rotate at different rates
(slower at poles, faster at equator)
(slower at poles, faster at equator)
��`Surface*
`Surface*’’gravity is 2.5
gravity is 2.5��
that of Earth
that of Earth
��Escape velocity is 6 tim
es that of Earth
Escape velocity is 6 tim
es that of Earth
��Magnetic field is 14
Magnetic field is 14��
stronger than Earth
stronger than Earth’’ ss
��Radiates more energy at infrared wavelengths
Radiates more energy at infrared wavelengths
than it receives from the Sun
than it receives from the Sun ––
slowly
slowly
collapsing and releasing energy
collapsing and releasing energy
*gra
vity at the to
p of the atmosp
her
e
Great Red Spot
Great Red Spot
Gre
at R
ed S
pot an
d
Earth
(to
sca
le)
Red
Spot is an
ancien
t hurricanein
Jupiter’s atm
osp
her
e –
Win
d spee
ds 650 km s
-1
Diameter
is over
twice th
at of Earth
Circu
lation ban
ds sh
ow it is
rotating
Origin of colou
ris not fully und
erstoo
d, m
ay be do
wn to red
pho
spho
rus
Jupiter
Jupiter ’’s Atm
osphere: Convection
s Atm
osphere: Convection
��Zones
Zones --light (heating,
light (heating,
high pressure), Belts
high pressure), Belts --
dark (cooling, low
dark (cooling, low
pressure)
pressure)
��Zones flow in the
Zones flow in the
opposite direction to
opposite direction to
belts
belts
Zones
, belts w
rap aro
und the planet bec
ause
of the fast rotation
Cloud motion
Cloud motion
��Clip shows projected surface of Jupiter over 10
Clip shows projected surface of Jupiter over 10
days, as shot by
days, as shot by Cassini
Cassini --Huygens probe
Huygens probe
New
New ““Junior
Junior ””
Red Spot
Red Spot
App
eared in 2
006, an
d seem
s to hav
e be
en formed
by the merger of
two othe
r storms
Jupiter
Jupiter ’’s Atm
osphere
s Atm
osphere
�84% H
ydrogen, 15%
Helium
�Very chem
ically complex,
subtle reactions depend on
temperature and pressure
�We see the upper N
H3
(ammonia) ice clouds as
white regions
�The am
monium
hydrosulfide (N
H4H
S) ice
clouds are seen as dark
regions
Life on Jupiter?
Life on Jupiter?
��In the 1970
In the 1970’’ s (prior to Voyager missions)
s (prior to Voyager missions) Sagan
Sagan
&
& Salpeter
Salpeter
hypothesized that ammonia based life could evolve in Jupiter
hypothesized that ammonia based life could evolve in Jupiter’’ s s
atmosphere
atmosphere
��The idea was adopted by many science fiction authors but quickly
The idea was adopted by many science fiction authors but quickly
Voyager data proved the hypothesis fundam
entally flawed
Voyager data proved the hypothesis fundam
entally flawed
��In practice this seems incredibly unlikely for the following
In practice this seems incredibly unlikely for the following
reasons:
reasons:
��Winds range from 200 to 1600 km
hWinds range from 200 to 1600 km
h-- 11
��Tem
perature ranges are vast, from
Tem
perature ranges are vast, from --167
167°°C to 0
C to 0°°CC
��Where the temperature reaches 0
Where the temperature reaches 0°°C the pressure is equivalent to being
C the pressure is equivalent to being
under 2 m
iles of water on the Earth
under 2 m
iles of water on the Earth
��Large amounts of electrical discharge
Large amounts of electrical discharge
Contribution of Jupiter to life on
Contribution of Jupiter to life on
Earth
Earth
��Jupiter
Jupiter’’ s gravitational pull is sufficiently large to deflect
s gravitational pull is sufficiently large to deflect
a large fraction of comets and
a large fraction of comets and planetesimals
planetesimalsheading for
heading for
the inner solar system
the inner solar system
��This helps reduce the probability of an im
pact event
This helps reduce the probability of an im
pact event
that could wipe out life on Earth
that could wipe out life on Earth
��However, Jupiter cannot be too m
assive as some
However, Jupiter cannot be too m
assive as some
comets must reach the primordial E
arth to supply it
comets must reach the primordial E
arth to supply it
with water
with water
��The balance between having enough m
ass and having to
The balance between having enough m
ass and having to
much m
ass is part of the Rare Earth hypothesis
much m
ass is part of the Rare Earth hypothesis
Jovian
JovianSatellites
Satellites
��Jupiter has at least 60 m
oons of sizes
Jupiter has at least 60 m
oons of sizes
greater than 3km
greater than 3km
��However there are 4 major satellites
However there are 4 major satellites
(diameter greater than 3000km)
(diameter greater than 3000km)
��Io,
Io, Europa
Europa , G
anym
ede,
, Ganym
ede, Callisto
Callisto
��Io shows extrem
e volcanic activity
Io shows extrem
e volcanic activity
due to stresses caused by
due to stresses caused by Jupiters
Jupiters
tidal field
tidal field
��Ganym
ede,
Ganym
ede, Callisto
Callisto
and
and Europa
Europaall
all
show evidence of liquid water
show evidence of liquid water
beneath their surfaces
beneath their surfaces
��The presence of trace am
ounts of
The presence of trace am
ounts of
organic m
olecules have been found
organic m
olecules have been found
on G
anym
ede and
on G
anym
ede and Callisto
Callisto
Europa
Europa ��
Frozen surface of water ice
Frozen surface of water ice
(100 km thick?)
(100 km thick?)
��Surface temperature ~
Surface temperature ~ --160 C
160 C
��Very few surface craters
Very few surface craters
indicates a fairly new
surface
indicates a fairly new
surface
��No organic m
olecules have
No organic m
olecules have
been detected on surface, but
been detected on surface, but
we don
we don’’ t know about under the
t know about under the
ice sheet
ice sheet
��Possibility of subsurface ocean
Possibility of subsurface ocean
due to heat from tidal heating
due to heat from tidal heating
of the planet caused by Jupiter
of the planet caused by Jupiter
��Requires a probe to be sent to
Requires a probe to be sent to
test the idea
test the idea
��Water + heat + organic
Water + heat + organic
molecules=
possibility of life?
molecules=
possibility of life?
We’ll
spen
d a lectur
e look
ing at this po
ssibilt
y…
Saturn
Saturn
Saturn
fro
m V
oyag
er 1 after
it’s fly-b
y
Saturn Facts
Saturn Facts
��Diameter 120,000 km
Diameter 120,000 km
��Saturn is
Saturn is less de
nse
less den
se than water
than water
��Rotation period about 10 hours
Rotation period about 10 hours
��Escape velocity is about 3
Escape velocity is about 3��
Earth
Earth’’ ss
��`Surface
`Surface ’’gravity: approx same as Earth
gravity: approx same as Earth
��Ring system
form
ed from break
Ring system
form
ed from break-- up of
up of planetesimals
planetesimals
��Has very large satellite system like Jupiter and also
Has very large satellite system like Jupiter and also
emits more energy at infrared wavelengths than it
emits more energy at infrared wavelengths than it
receives from the Sun
receives from the Sun
Saturn
Saturn’’ s Atm
osphere
s Atm
osphere
��92.4 %
Hydrogen, 7.4 %
92.4 %
Hydrogen, 7.4 %
Helium
Helium
��Less Helium because it is
Less Helium because it is
condensing out and raining
condensing out and raining
down on the center of the
down on the center of the
planet
planet
��Very similar to the
Very similar to the Jovian
Jovian
atmosphere
atmosphere
��Equally inhospitable
Equally inhospitable
��Less dense, so pressure
Less dense, so pressure
does not rise as fast with
does not rise as fast with
depth
depth
Titan
eclipsing
the
Sun
, the sm
all moo
n is E
ncelad
us
Aurora on Saturn
Aurora on Saturn
Pictu
re fro
m the
Hubble S
pac
e
Teles
cope
Occ
ur on
oth
er planets
too
Titan
Titan
��Titan is the only m
oon in the solar system
with a thick
Titan is the only m
oon in the solar system
with a thick
atmosphere
atmosphere
��Visible wavelengths do not penetrate the haze
Visible wavelengths do not penetrate the haze ––high
high albedo
albedoso Titan is
so Titan is
colder than we might expect
colder than we might expect
��Surface temperatures around
Surface temperatures around --179
179°°CC
��Liquid m
ethane precipitation?
Liquid m
ethane precipitation?
��The Huygens probe landed on the surface and sent some
The Huygens probe landed on the surface and sent some
stunning images back
stunning images back
��Strong evidence for lakes of hydrocarbons
Strong evidence for lakes of hydrocarbons ––first liquid bodies observed
first liquid bodies observed
beyond Earth
beyond Earth
��Evidence of erosion
Evidence of erosion
��Other than tem
perature Titan has a number of similarities with
Other than tem
perature Titan has a number of similarities with
primordial Earth
primordial Earth ––
we
we ’’ll spend a lecture looking at this in m
ore
ll spend a lecture looking at this in m
ore
detail
detail
Artist’s im
pression
of Titan
’s sur
face
Sou
nd of Titan
from H
uygens
probe
Uranus
Uranus
��HST picture at infrared wavelength
HST picture at infrared wavelength
Very plain at
visible w
avelen
gths!
Clo
uds
Uranus Facts
Uranus Facts
��Axial tilt 98
Axial tilt 98o
o --poles almost lie on ecliptic
poles almost lie on ecliptic
��Diameter: about 50,000 km
Diameter: about 50,000 km
��Rotation period: about 17 hours
Rotation period: about 17 hours
��Escape velocity about 2
Escape velocity about 2��
Earth
Earth’’ ss
Neptune
Neptune
Rin
g system
not
visible on this pictu
re
Neptune Facts
Neptune Facts
��Discovered in 1846 following realization
Discovered in 1846 following realization
that Uranus
that Uranus ’’s orbit was being perturbed
s orbit was being perturbed
��Diameter: 50,000 km
Diameter: 50,000 km
��Rotation period: 17 hours
Rotation period: 17 hours
��Slightly more m
assive than Uranus
Slightly more m
assive than Uranus
��Exhibits massive storm
systems
Exhibits massive storm
systems ““Great
Great
dark spot
dark spot ””
but dissipation occurs rapidly
but dissipation occurs rapidly
(visible in 1989 but not 1994)
(visible in 1989 but not 1994)
Trito
n
Summary of lecture 13
Summary of lecture 13
��Life evolving in the
Life evolving in the Jovian
Jovian
planets
planets
them
selves seems virtually impossible
them
selves seems virtually impossible
��However, a number of satellites show
However, a number of satellites show
evidence for liquid water, heat and organic
evidence for liquid water, heat and organic
monomers which together could form
the
monomers which together could form
the
basis of life
basis of life
Next lecture
Next lecture
��Terrestrial planets
Terrestrial planets