Planetesimal Ejection
Larger “debris” leftover from creating the planets are either
captured as moons of the larger planets, or the gravity of the
planets guides the debris into the asteroid belt, Kuiper belt, or
Oort cloud.

Asteroids and meteoroids are small
objects made of mainly rock and
metal. They are found primarily in
and around the Inner Solar System.
The only difference between the two
is size. Asteroids are all larger than
100 meters in diameter, or have a
mass more than 10,000 tons -
meteoroids are smaller.

Inner Solar System
Asteroids and
meteoroids are usually
found near the plane of
the solar system.
Those orbiting between
Mars and Jupiter are in
the asteroid belt, while
those in Jupiter’s orbit
are in the Trojan
regions.
Some of these asteroids and meteoroids come closer to the
Sun. Those that cross the orbit of Earth are called Apollo
asteroids.

A meteor is seen when any comet, asteroid, or meteoroid
enters the Earth’s atmosphere. The “shooting star” you see
is a meteor.
A meteorite is the chunk of rock or metal that has reached
the surface of the Earth from space.
A meteoroid is a small chuck of rock or metal that orbits
the Sun

Why does this asteroid look
“weathered”?
Like a rock you might find on a
beach?
Everything gets hit by meteoroids!

Meteor Trail

Barringer Crater
Meteoroids are constantly
hitting the Earth. Most of
these meteoroids are the
size of grains of sand or so.
They make short quick
meteor trails visible only at
night. Usually you can see
about 1 or 2 an hour.
Larger meteors are very
rare.
Big meteoroid strikes like the one that produced Barringer Crater
(the meteoroid was about 50 meters across and hit with an
energy of few megatons of TNT) occur once every few thousand
years.

Tunguska Debris
The most recent event
was in 1908 in
Tunguska, Siberia.
We are not sure if the
object was a meteoroid
or a comet, but it
exploded in midair with
an energy of about 20 to
40 megatons of TNT!
We think that asteroid impacts are even more rare. We guess
that they occur once every 600,000 years or so. Such impacts
would be large enough to cause global climate changes - a
“nuclear winter”.

The leading theory about the
extinction of the dinosaurs of
course involves an asteroid impact.
All over the world you can see
evidence for this in the K-T
boundary in geologic strata
(layers).

Comets
Unlike asteroids and meteoroids, comets are made up of ices -
frozen water, CO2, and possibly other lighter gasses - and also
rock and dust. As the ices evaporate off the comet, a cloud
called the coma is formed around the nucleus. The solar wind
and radiation pushes the gas and dust away from the nucleus to
form the tail.

Halley’s Comet Closeup

Comet Tails
There are usually two
tails for a comet, and ion
tail and a dust tail. The
ion tail is made of ionized
comet material and is
pointing directly away
from the Sun. The dust
tail is curved as the dust
particles orbit around the
Sun after getting
released by the comet.

Meteor Showers
As Earth passes through the
debris path of a comet,
observers on Earth can see
many many meteors coming
from the same general area of
the sky. These meteor
showers or storms are often
named for the constellation
that they seem to “come
from”.

Comet Reservoirs
We believe that
most objects in the
Kuiper Belt and Oort
cloud are made of
ices and rock.
Since they are so far
form the Sun, even
oxygen and nitrogen
will turn to ice!
Long period comets are thought to mainly come from the
Oort cloud.
Short period comets (like Halley’s) are thought to come from
the Kuiper belt.

The Discovery of Pluto
After the discovery of Neptune,
astronomers still thought another planet
might (but they were wrong) be
influencing the orbits of Uranus and
Neptune. In 1930 Clyde Tombaugh
discovered Pluto while looking for this
new planet. Pluto is the only planet we
have not explored with a spacecraft. The
New Horizons craft should get there in
2015!

Pluto and Charon
Pluto and its moon are both probably Kuiper Belt objects. By
measuring their size and mass we can calculate their density. From
this we believe are mainly made up of rock and ice, very similar to
Europa, Ganymede, Callisto and Triton.

Pluto
A fuzzy map of Pluto made from Hubble Telescope images.

The Hubble telescope has just recently discovered two new moons
around Pluto. In 2006 they were given the names of Nix and Hydra.
The appear to be in the same plane as Charon, so their formation
should be related.

KBOs Compared
In the last few years several Kuiper Belt
objects have been found. And several
even have their own moons.
There are at least 11 KBOs with
diameters of 1000 km or more. M. Brown/Keck Observatory

Pluto’s Demotion
RESOLUTION 5A
The IAU therefore resolves that planets and other bodies in our Solar
System, except satellites,be defined into three distinct categories in the
following way:
(1) A "planet"1 is a celestial body that (a) is in orbit around the Sun, (b)
has sufficient mass for its self-gravity to overcome rigid body forces so
that it assumes a hydrostatic equilibrium (nearly round) shape, and (c)
has cleared the neighbourhood around its orbit.
(2) A "dwarf planet" is a celestial body that (a) is in orbit around the Sun,
(b) has sufficient mass for its self-gravity to overcome rigid body forces so
that it assumes a hydrostatic equilibrium (nearly round) shape2, (c) has
not cleared the neighbourhood around its orbit, and (d) is not a satellite.
(3) All other objects3, except satellites, orbiting the Sun shall be referred
to collectively as "Small Solar System Bodies".
IAU - INTERNATIONAL ASTRONOMICAL UNION web site - http://www.iau2006.org/mirror/www.iau.org/iau0602/index.html

Planet X
Astronomers once thought that another large planet (Earth size
or bigger) might exist far out in the Kuiper belt or Oort cloud.
In fact Pluto was found searching for planet X. Such a planet
could disrupt the orbits of objects out there, and send them in
toward the inner Solar System, where we see them as comets.
So far we have no evidence that “planet X” exists. However we
have searched only a small fraction of the Kuiper Belt, and know
even less about the Oort cloud.

Stellar Balance
Our Sun lives in a
state of balance....
between the force of
gravity pushing in....
and the pressure from
fusion pushing out.

Solar Composition
Change
As stars burn Hydrogen into Helium the amount of Helium
in the star’s core builds up.
At this point in the star’s life the temperature in its core is not
high enough to fuse Helium into other elements, so the
Helium just sits there inert.

Solar Composition
Change
When the amount of Helium builds up to a
certain level, fusion at the center of the core
stops, with fusion only occurring in a shell
surrounding the non-burning Helium.

The center of the core is now no
longer being
pushed out by the energy produced
from fusion. As the amount of Helium
“ash” grows, gravity starts to
compress it.
As the core is compressed the
temperature goes up until Helium can
be fused.
Since the temperature of the core is much higher than before,
the core is producing a lot more energy. This extra energy
“pushes out” the rest of the star and the star gets
bigger!
So as the core gets smaller the rest of the star gets larger!

We see many
different stars in our
galaxy. Some stars
are enormous Red
Giants that are
hundreds of times
larger than our Sun.
Will our Sun ever
become a Red Giant?
YES!
How? When?

Red Giant
When this happens to
our Sun in about 4
billion years our Sun will
expand to possibly
engulf the Earth!

Now Helium is being fused into Carbon, and the process
repeats, the core shrinks and gets hotter, but our Sun is
not large enough for Carbon fusion to start…

G-Type Star Evolution
Throughout the stars life, as the star uses up its fuel, the core
continues to shrink, the core temperature continues to rise,
and more and more energy is being emitted by the core, and
the star gets larger and larger until…

Planetary
Nebulae

White Dwarf
on H–R Diagram
After all the fuel is
gone, and the star
has made a nebula,
all that is left is a
White Dwarf
This is the leftover
core of the old star, it
is very small (Earth
sized) and very hot

White dwarfs shine only due to stored heat, as
they cool they grow fainter and fainter.
Eventually (trillions of years from now) they
will be cold enough to stop emitting light
altogether,

If the star is massive enough the temperature in the core of the
star can get high enough (1 billion K) to start the fusion of
Carbon into heavier elements like Aluminum, Neon, and
Sodium. When this happens, the core shrinks again and the
star expands again.

Stars that are massive enough to produce temperatures up
to 4 billion K can burn all the elements up to Iron in their
cores.
These stars can grow up to 1000 times the size of our Sun
- Supergiants!

Heavy Element
Fusion
Iron is the stopping
point for any star,
fusing Iron into
heavier elements
does not release
energy. Fusion still
continues around
the iron core,
which keeps
growing.
In the iron core, there is no fusion to create an outward pressure
to counteract the force of gravity.

Core collapse
supernova
The iron core of the star
that is about the size of
the Earth. The iron in the
core is made up of ...
protons (+)
neutrons (0)
electrons (-)
Most of the space inside an atom is taken up by the electrons.
When the Iron core of a star reaches critical mass called the
Chandrasekhar mass (1.4 times the mass of our Sun) the
force of gravity is too great and the protons and electrons get
“squeezed” together to make neutrons.

Core collapse
supernova
Now the core of the star
is made up of just
neutrons (0) !!!
Without electrons around
to take up space, gravity
can cause the core to
collapse.
In about 1 minute or so the core (that was supporting the
weight of the entire star) collapses from the size of the Earth to
the size of Chicago (~10 miles across). The rest of the star
collapses onto the core and then “bounces”.

Supernova 1987A
The core becomes a Neutron star and we see a Supernova!
This core-collapse supernova is also called a type II supernova.

Over the time period of just a few days, a supernova can
emit as much energy as our Sun will in its 10 billion year
lifetime.

Supernova Light Curves
Astronomers can tell
the two types of
supernovae apart by
looking at how bright
the supernova is
over a period of time.
Also astronomers can distinguish the two types by looking at a
spectrum and seeing how much hydrogen was present in the
explosion. A type I (carbon-detonation) supernova has very
little hydrogen present, unlike a type II (core-collapse)
supernova.

Supernova Remnants
In our galaxy we estimate
there is a type I and a type II
supernova about once every
100 years. The last one that
we saw in our galaxy was in
1604....so we are due!
We do see supernovae quite
often in other galaxies.

Supernova 1987A
This supernova was the
closest in recent history,
and the only one where we
were able study it
accurately.

Neutron Stars
Neutron stars are extreme
objects
Density: 1015 g/cm3
Temperature: 1012 K when
born
Magnetic Field: 1012 times
stronger than Earth’s
Spin: from 60 rpm to 38,000
rpm

Curved Space
Newton’s Law of Gravity:
The force between mass m1 and
mass m2 is....
F = Gm1m2/R2
So if an object has no mass, there
should be no force on it due to
gravity!
Einstein: Mass causes space itself to
curve and warp, and objects travel
on this surface....

Tests of General Relativity
The first test of Einstein’s theory of general relativity came
when we measured how the gravity of our own Sun can bend
light.

Gravitational
Redshift
The gravity of a black
hole is so strong, that
light can not escape!
The region where this is
true is inside the event
horizon.
The event horizon is
NOT the surface of the
black hole. It is just the
boundary between
where light can escape,
and where it can’t!

Black Holes
Black holes are formed when
you compress an object to a
size smaller than the
Schwarzschild radius for that
object.
For the Earth it is about 1 cm
For Jupiter it is about 3 m
For our Sun it is about 3 km.
The only force strong enough that we know of to produce a
black hole is a type II (core-collapse) supernova. Even then
only very massive stars will end up as black holes.

Black Holes
If you were far from the black
hole, you would feel no unusual
effects. In fact if our Sun
suddenly became a black hole
the Earth would simply keep
orbiting it like usual.
As you approach a black hole
the gravity gets stronger, and
the tidal forces start to stretch
you.
If you could survive to come close to the black hole, you would
observe severe distortions in both space and time as predicted
by Einstein!

Robot–Astronaut
What is IN a black hole?
We believe that all matter could
be compressed to a singularity!
A point of infinite density and
zero size.
BUT....
There is no way to find out!

The Solar System
There are three kinds
of objects in our Solar
System (other than the
Sun)
Terrestrial planets
Jovian planets
and other stuff.....
asteroids, comets, and
meteoroids

Sun and Planets - Relative Sizes

This is the Eagle nebula as
seen by the Hubble
telescope.
Fusion creates elements
heavier than hydrogen and
helium, and supernovae
disperse these elements
out into the galaxy.
The dust and gas seen
here is probably made up
of gas from the Big Bang
and also from many
supernovae.
This gas and dust is the raw materials that stars and solar
systems are made out of.

Right now, new stars and solar
systems are being formed in
this cloud of gas and dust.
As intense radiation from stars
just outside the cloud “blow” the
cloud away, we can see small
clumps of denser regions of gas
and dust being revealed.
In each of these clumps is a solar system that is forming, each
with a sun that could someday be much like our own, and each
perhaps with planets like Earth.

It all starts with a cloud of gas and dust. The gravitational
attraction between the gas and dust particles slowly causes
the cloud to collapse, to contract. This causes all of the
matter in the cloud to become more concentrated.
Because the initial gas cloud had some rotation, as the
collapse happens this rotation speeds up, and the cloud
flattens out into a disk.
This is due to something called conservation of angular
momentum.

In the center of the disk the gravity is the strongest, so most of
the mass in the solar system accumulates there. This will
become a protostar.
The rest of the material
starts clumping together
in orbit around this
central mass. Larger
clumps condense out of
the gas and dust.

These clumps then start to join together in a snowball
effect. This forms planetesimals.

During this time a protostar has
formed. It is bigger than our Sun,
but not as hot yet. The temperature
in the core is not hot enough for
fusion to start. Once fusion starts, it
becomes a star!

Beta Pictoris

The Virial Theorem
How does the dust and gas in the cloud heat up as it collapses?
A small part of the cloud that is far away from the center of the
cloud has a lot of gravitational potential energy. As this small part
of the cloud “falls” closer to the center, it loses potential energy and
gains kinetic energy. It starts moving faster.
However, the cloud is spinning, and the faster the small part of the
cloud moves, the farther away from the center orbits.
So how does the cloud collapse? The small part of the cloud needs
to lose both potential and kinetic energy. It does this by turning
potential and kinetic energy into heat! Gas molecules and dust
grains hit each other, and these collisions turn kinetic energy into
heat and the temperature of the cloud goes up!

The Virial Theorem
You can derive an equation from Newton’s laws that shows how
much energy the gas and dust will turn into heat as it slowly spirals in
toward the center of the cloud.
This equation is called the virial theorem.
Basically what this means is that as matter collects to form a large
object, like the Sun, Earth or even our Moon, the matter heats up to
higher temperatures.
This is how the temperature in the center of our protostar got high
enough (10 million Kelvin) for fusion to start.
This is one of the reasons why the center of the Earth is hot enough to
melt metal.

The planetesimals in orbit around the protostar are still growing
larger, accumulating more and more material.
Eventually the planetesimals all clump together and form
protoplanets! These have roughly the right sizes as our planets
do today, but they are not quite done growing yet.

Temperature in the Early Solar Nebula
Because of the higher temperatures in the inner solar system the
protoplanets near the protostar were very different than those
farther away. The near protoplanets were made of mostly rock
and metal, with very little hydrogen, helium, oxygen, water,
nitrogen, or other lighter chemicals
The protoplanets that
were farther out were
made more out of the
lighter chemicals.
Since there were more
of these lighter
materials than anything
else in the early solar
system the outer
planets became much
larger.

When fusion starts and our Sun is born, it starts emitting huge
amounts of energy.
The enormous amounts of
radiation and solar wind that
the new star produces
“blows” or “pushes” away all
of the dust and gas that is
leftover from the production
of the planets.
http://sohowww.nascom.nasa.gov/

The new planets in the solar system looked nothing like what
we see today.
Planets were all very hot, the inner planets were all
completely molten.
The atmospheres of all the planets
were mainly made of hydrogen and
helium. The smaller planets like
Earth didn’t have a strong enough
gravity to hold on to this
atmosphere for very long.
The planets were undifferentiated -
meaning they did not have different
regions made of different materials.

Planetesimal Ejection
Larger “debris” leftover from creating the planets are either
captured as moons of the larger planets, or the gravity of the
planets guides the debris into the asteroid belt, Kuiper belt, or
Oort cloud.

Comet Reservoirs

By learning about the Earth we
can make comparisons to the
other planets and understand
them better.

The Earth
Earth has a ....
magnetosphere
atmosphere
hydrosphere
crust
mantle
and an outer and inner
core

Planetary Science
All the different parts of
the Earth ....
- magnetosphere
- atmosphere
- hydrosphere
- crust
- mantle
- core
... affect each other. The
dynamics of how
processes in these
regions affect the planet
is called Planetary
Science.

Earth’s Interior
The interior of the Earth is differentiated because the Earth
was completely molten at some point in its history.
Both radioactivity and asteroid impacts supplied the heat to
melt the Earth.

Seismology
Seismology is the study of
how shock waves from
earthquakes travel through
the Earth.
We can learn about the
density of the interior of
the Earth this way much
like an ultrasound test can
see inside people
Sudden changes in density can cause these waves
to be reflected or refracted. Seismic waves also can
show if the material is solid or liquid.

Earth’s Interior
From seismology we know that the Earth’s core is much
more dense than the silicate based mantle and crust, and
the core is made of a solid center, and a liquid outer region.
From the density
measurements made
using seismology we
believe that the core is
mostly made of iron,
with some nickel

Plate Drift
Earth is a very geologically active place with volcanoes and
plate tectonics. The mantle is semi-molten, with convection
slowly causing hotter material to rise and cooler material to fall
in the mantle. The tectonic plates of the Earth “float” on these
convection currents.

Global Plates

Seismology
Here you see the
seismic waves from the
2004 Sumatra
earthquake. You can
see how the seismic
waves could still be
detected even after
going around the world
almost two times

Earth’s Magnetosphere
Magnetohydrodynamics is
the study of how electrically
conductive fluids behave.
Because the Earth’s core is a
rotating and convecting
system of a metallic liquid,
strong electrical currents are
produced in the Earth’s core.
This produces the Earth’s
magnetic field!

Earth’s Magnetosphere
Computer calculations using magnetohydrodynamics have
shown that if a planet does not have
• a conducting liquid
• convection
• and rotation
The planet will not have a strong magnetic field like the Earth’s.

Van Allen Belts
The Earth’s magnetic field deflects and traps particles from
the Solar Wind. The trapped particles are located in two
regions called the Van Allen belts.

Aurora Borealis
Some of the Solar Wind makes it through the Earth’s magnetic
field and hits our atmosphere making it glow. This usually
happens at the North and South poles – the Aurora Borealis
and the Aurora Australis

Earth’s Atmosphere

Convection
Most of Earth’s weather occurs in the troposphere. Weather
on Earth is driven by convection, warm air rising and colder
air falling.

The Greenhouse Effect and Global Warming
Over the last two decades
evidence has been growing
that the Earth’s atmosphere
is getting warmer.
Most likely this is due to
human activity. It is
possible that this rise in
temperature is linked to the
increase in “greenhouse
gases” like CO2 in the
atmosphere.

Greenhouse Effect
The Greenhouse effect refers to the “blanket like” effect that
certain gases have.
These gases absorb and re-emit infrared radiation, which
prevents this radiation from escaping to space so easily.

Hydrosphere
Ocean currents – like the thermohaline current shown here –
can have a profound effect on the climate by the
transportation of energy (heat) and matter (dissolved gasses).

Lunar Tides

Lunar Tides
The force of gravity
decreases with increasing
distance. This is responsible
for the tidal force effect.
This effect causes the Earth
to very slightly deform or be
stretched by the moon’s
gravity.
Since water is more free to move than solid ground, we see
this effect mostly in the Earth’s oceans – the tides.
In the open ocean this effect is quite small only about
a 1 meter high bulge.

Solar and Lunar Tides
The Sun also produces a
tidal effect on the Earth
but it is much smaller
than the moon’s effect.
The largest tides are the
Spring tides when the
Sun, Moon, and Earth
are all roughly in a line.
The smallest tides are
the Neap tides when the
Moon and Sun are at
right angles to the Earth.

Tidal Bulge
The Tides on Earth are not
directly in line with the Moon.
Since the tidal bulge is
offset, the Moon can affect
the Earths rotation, and the
Earths rotation can affect the
Moon’s orbit! This is causing
the Earth’s rotation to slow
down, and the Moon to
mover farther away from the
Earth.

Tidal Bulge
Just like the moon produces a
tidal bulge on Earth, the Earth
makes a tidal bulge on the moon.
Over time the effect of Earth’s
gravity on the moon’s tidal bulge
changed the rotation of the moon.
This is why the same side of the
moon always faces the Earth.
This is called tidal locking. The
Moon’s orbit and rotation are
tidally locked or synchronized.

Tidally locked means
that the time it takes
for the Moon to rotate
is the same as the
time it takes to orbit
the Earth. So we can
only see one side of
the Moon from Earth.

Tidal Bulge
The Earth’s rotation is not yet
synchronized with the Moon’s
orbit. The Earth’s rotation will
keep slowing down, and the
Moon will keep moving away
until they become tidally
locked, and only one side of
the Earth will face the
Moon.... many billions of
years from now.
The Earth’s rotation is slowing
at a rate of 0.002 seconds per
century and the Moon is
moving away 3.8 cm per year.

Full Moon, Near Side
There are two different kinds
of surfaces on the near side
of the moon.
Maria – flat, darker regions
that are made of younger
material. Produced by lava
flows.
Highlands – older, lighter
colored regions with many
mountains and craters

Full Moon, Far Side
On the far side
we find mainly just
highlands and very
few maria.

The Moon
Since the moon is
differentiated, it too was
molten at some time in
its history.
However not a lot is
known about the interior
of the moon.
We believe that the core
of the Moon is no longer
molten.

Moon, Close Up
When the Moon was
younger and its crust
was thinner and its
interior still molten, we
believe that the crust
cracked and lava flowed
up through these cracks
and formed the maria.

Meteoroid Impact

Lunar Surface
A layer of dust covers
the surface of the
Moon. This dust is
caused by the many,
many impacts of
meteoroids that
continually occur on
the Moon.

Lunar The dominant theory of how
Formation our Moon formed is the Impact
Theory – which says a
protoplanet about the size of
Mars hit the Earth shortly after
the Earth formed

Lunar Formation
A fraction of the
debris from this
impact collected
together to form our
Moon.

The Terrestrial Planets

The Messenger spacecraft
We were not able to learn much about Mercury from Mariner
10 (the only spacecraft to visit Mercury). The Messenger
spacecraft is on its way to Mercury right now, it will do 3 flybys
of Mercury in 2008 and 2009, and then go into orbit in 2011.
Since Messenger is more modern and advanced than Mariner
10, we will learn much much more.

Mercury’s Rotation
Mercury’s rotation (59
days) is tidally locked to
2/3 of an orbital period
(88 days). Its orbit and
rotation is not
synchronized like our
Moon’s because
Mercury’s orbit is
eccentric (more elliptical
than the orbits of most
planets). This means
that one “day” (from
noon to noon) on
Mercury lasts 176 Earth
days!

108

Because it is so small
the core of Mercury is
probably mostly solid,
meaning that scientists
did not expect to find a
magnetosphere!
One the scale shown the
Earth’s field would
register at around
50,000nT, so we think
that something very
different is causing
Mercury’s magnetic field.

Mercury’s Surface
Mercury’s surface has a large number of these scarps or cliffs
like giant cracks in its surface.
Mercury never had plate tectonics like the Earth. When the crust
of Mercury cooled it shrank causing the crust to crack.

Venus, Up Close
Because of Venus’s dense
cloud cover most of what
we know about Venus’s
surface and rotation comes
from using radar.
There has been only a few
spacecraft to land on Venus,
but each survived for only a
short time.

The Atmosphere of Venus
The atmosphere of Venus is
made up of carbon dioxide,
with clouds of sulfuric acid.
The atmosphere is some 90
times denser than Earth’s.
The Greenhouse effect
causes the surface
temperature of Venus to be
close to 730K day or night.
This is warmer than even Mercury which is a lot closer to the
Sun! Venus is far too hot for gases lighter than CO 2 to stay in
its atmosphere. Venus has almost no water, O 2, or N2.

Venus Magellan Map
In 1995 the Magellan
spacecraft was able
to make a much more
detailed radar map of
Venus.
Possibly active shield
volcanoes, craters,
and volcanic structures
called coronae were
seen by Magellan.

Venus’s Surface Features
pictures from Magellan
spacecraft NASA/JPL

Venus Corona and Volcanoes
Venus has several times more
volcanoes as Earth does, however
Venus does not have plate
tectonics like Earth. This could be
why the surface of Venus appears
older than Earth’s surface (~500
million years vs. ~100 million).
pictures from Magellan
spacecraft NASA/JPL
We can not tell from these radar
images if Venus is geologically
active right now, but we believe it
could be active. We believe that
Venus is much like a “young” Earth
was just before Earth’s oceans
formed.

Venus
Venus has no detectable magnetosphere, probably due in
part to Venus’s very slow rotation rate and a lack of
convection in the core.
We expect Venus to have a crust, mantle and a core like
Earth

Venus in Situ
This is one of the few pictures of the surface of Venus that we
have. There have only been 6 Russian landers (no US) each
lasting only an hour or two before running out of power.

Terrestrial Planets’ Spin
While Venus is the planet that is closest in size to the Earth,
Mars has a rotation rate (24.6 hours) and a tilted axis (24
degrees) that are very similar to Earth.

Mars, Up Close
The rovers have made many
rock and soil measurements.
The main components of this
sample were silicon, iron, and
calcium. The Martian soil is
rich in iron, which is why is is
red.

Mars Atmosphere
Picture taken by
Spirit of a sunset on
Mars.
Mars has a very thin atmosphere (less than 1% of Earth’s) of
mainly carbon dioxide. The surface temperature is around 50K
lower than Earth’s, but would be colder without the greenhouse
effect.
These temperatures were taken by a combination of the Mars
Global Surveyor and the rover Opportunity.

Water on Mars
Because of orbiter pictures and geologic studies done by the
rovers we are now fairly confident that large amounts of liquid
water was present at some time on Mars.

Water on Mars
NASA/JPL

Martian Outflow
Where is all of this water
now? Most of it was probably
lost when Mars lost it’s
atmosphere, but some of it
might still be there, frozen
under the surface.
Scientists believe that because Mars is so small and so far from
the Sun, that the planet cooled off much faster than the Earth did.
When the core of the planet started to solidify it started to lose its
magnetosphere. Mars lost almost all of its atmosphere due to a
combination of being exposed to the Solar wind, and having
much weaker gravity than Earth.

Martian Outflow
We have seen evidence
for liquid water maybe
existing on the surface
of Mars recently.
NASA/JPL/Malin
Space Science
Systems

Life on Mars?
We still do not have absolute proof that life existed on
Mars. But we think it is possible that it did long ago.

Planetesimal Ejection
Larger “debris” leftover from creating the planets are either
captured as moons of the larger planets, or the gravity of the
planets guides the debris into the asteroid belt, Kuiper belt, or
Oort cloud.

Inner Solar System
Most asteroids and
meteoroids are usually
found orbiting between
Mars and Jupiter are in
the asteroid belt.
Some of these asteroids come closer to the Sun. Those that
cross the orbit of Earth are called Apollo asteroids.

Why does this asteroid look
“weathered”?
Like a rock you might find on a
beach?
Everything gets hit by meteoroids!

Barringer Crater
Meteoroids are constantly
hitting the Earth. Most of
these meteoroids are the
size of grains of sand or so.
They make short quick
meteor trails visible only at
night. Usually you can see
about 1 or 2 an hour.
Larger meteors are very
rare.
Big meteoroid strikes like the one that produced Barringer Crater
(the meteoroid was about 50 meters across and hit with an
energy of few megatons of TNT) occur once every few thousand
years.

Tunguska Debris
The most recent event
was in 1908 in
Tunguska, Siberia.
We are not sure if the
object was a meteoroid
or a comet, but it
exploded in midair with
an energy of about 20 to
40 megatons of TNT!
We think that asteroid impacts are even more rare. We guess
that they occur once every 600,000 years or so. Such impacts
would be large enough to cause global climate changes - a
“nuclear winter”.

The leading theory about the
extinction of the dinosaurs of
course involves an asteroid impact.
All over the world you can see
evidence for this in the K-T
boundary in geologic strata
(layers).

Jupiter’s Interior
The interiors of the
Jovian planets are
very different from
the Terrestrial
planets.
What we call the
“surface” of Jupiter is
really the top of the
the atmosphere.
Just like the Sun, Jupiter is made up of mostly hydrogen and
helium. The colorful clouds in Jupiter’s atmosphere are made
of ammonia, methane, water, and phosphorous and other
chemicals.

Jupiter’s Convection
Jupiter radiates about twice as much heat than it absorbs from
the Sun. All this energy drives Jupiter’s weather system.
The lighter colored zones are regions where warmer material
is rising, and the darker colored belts are regions where
material is sinking. All of this convection activity causes many
swirling “storm” systems to be present at any one time in
Jupiter’s atmosphere

The weather on Jupiter is
very dynamic and chaotic.
There are many storms or
“vortices” like these
pictured by the Galileo
probe.
All Jovian planets have
differential rotation -
meaning that different
regions of the planet
rotate at different rates.
Galileo mission Nasa/JPL

Jupiter
Most of what we have
learned about the Jovian
planets has come from
spacecraft.
Voyager I and II
Galileo and probe
Cassini and Huygens

Jupiter’s Storms
Galileo mission Nasa/JPL
Here you see two pictures
The largest of these storms is taken about 75 min. apart on
the Great Red Spot, first seen the dark side of Jupiter, the
by astronomers over 300 years white specks are lightning in
ago. It is so large the Earth Jupiter’s atmosphere, some
could easily fit inside of it. What 100 to 1000 times brighter
causes it and why it is red are than on Earth.
still mysteries.

Jupiter’s Interior
The “atmosphere”
ends about 20,000 km
below the surface. The
pressure is so great
here that hydrogen is
forced to become a
liquid, and acts like a
metal.
The very core of Jupiter is probably rocky and metallic, like
Earth, but probably larger and much more dense.

Pioneer 10 Mission
All the Jovian planets have
extensive magnetic fields
Jupiter’s extends well past
the orbit of Saturn!
Jupiter’s magnetic field is so
strong because of the large
sea metallic hydrogen that is
under the atmosphere.
If you could “see” Jupiter’s
magnetosphere, from Earth it
would look 5 times larger
than the full Moon!

Auroras on Jupiter and Saturn
Aurorae have been seen
on both Jupiter and
Saturn.

Saturn
Cassini is currently in
orbit around Saturn and
is continually sending
back more data about
Saturn and its moons.

Both Jupiter and Saturn
rotate in less then 10 hours.
This fast rotation rate gives
them a squashed look.
Saturn is very similar to
Jupiter in many ways.
Their atmospheres are
similar, with Saturn having
thicker upper level clouds,
so less of the more colorful
lower clouds can be seen.

Saturn’s Atmosphere
Saturn radiates three times as
much as it receives from the Sun
(unlike Jupiter that radiates only
twice as much).
We think that this extra heat is
coming from the helium in
Saturn’s atmosphere condensing
and forming “rain”. As this rain
falls its energy is turned into heat.
This also explains why there is
less helium in Saturn’s upper
atmosphere compared to Jupiter.

Jovian Interiors
Since Saturn is not quite as
large as Jupiter, its internal
pressures and temperatures
are not as high as those in
Jupiter, and so its region of
metallic hydrogen is not as
thick.

Saturn’s Weather
The weather on Saturn is
similar to Jupiter, however
there is no “Great Red Spot”
like storm on Saturn.
NASA/JPL/Space Science Institute

Some storms on Saturn have been
seen to rotate “backward”
compared to storms on Earth. This
has also been seen on Jupiter.
NASA/JPL/Space Science Institute

Saturn’s Cloud Structure
We have discovered a
strange hexagon
structure around Saturn’s
north pole…. And a
“hurricane” with a central
“eye” at Saturn’s south
pole.

Uranus and Neptune
Just one spacecraft (Voyager II) has visited Uranus and
Neptune
Both planets get their bluish color from methane in their
atmospheres.

Jovian Interiors
We believe both Uranus and Neptune are just smaller versions
of Jupiter and Saturn on the inside. Neptune emits more heat
than it absorbs (just like Jupiter and Saturn), but Uranus does
not!

Uranus’s Seasons

Jovian Magnetic Fields
Uranus’ and Neptune’s magnetic fields have strange
orientations, and are not at all aligned with the rotation of
the planet.

Other than the Earth’s Moon, there are only 6 other “major” satellites
in the Solar system: Io, Europa, Ganymede, Callisto, Titan, and
Triton. There are many many more satellites, but all of them are
smaller than these. Each of these moons are special and unique in its
own way.

The four moons of Jupiter discovered
by Galileo are called the Galilean
moons. Io orbits the closest to
Jupiter, followed by Europa,
Ganymede, and last Callisto.

Galilean Moon
Interiors
Io is the most geologically
active moon or planet in the
Solar System. Tidal forces
from Jupiter are constantly
deforming the planet. All of the
friction deep within the moon
causes numerous volcanoes to
be active on the surface.
We believe that Europa might contain a thick liquid water ocean
beneath a crust of solid ice. The tidal forces on Europa are not as strong
as they are of Io, but they are enough to keep its oceans from freezing
solid. Because there is liquid water on the moon, scientists believe
Europa is our best bet of finding life on a world other than our own!

Io

Europa

Galilean Moon Interiors Ganymede is the largest moon in
the Solar System, even larger than
Mercury or Pluto. Ganymede and
Europa both have a magnetic field.
We believe Ganymede has a thick
water/ice layer around a rocky
mantle and an iron core.
While we think Callisto is made up
of similar material as Ganymede,
Callisto is undifferentiated.
Basically no geological activity has
occured there since it was created
some 4.5 billion years ago. This
makes it the most heavily cratered
object in the Solar System.

Ganymede

Callisto

Titan

Titan’s
Atmosphere
Titan is the only moon to have a thick atmosphere. The
atmosphere is made up of mostly nitrogen and methane. The
methane on Titan acts very much like water does in the weather
here on Earth.

Huygens Probe
The Huygens probe appears to have
seen an ocean and rivers as it
descended to the surface of Titan. The
surface temperature on Titan is only 94
K (-350 F)! So there is no chance that
the ocean and rivers have liquid water,
instead they probably have liquid
methane.
Nasa/JPL/ESA
From data on how the probe landed,
it is believed that the probe landed in
“mud” or soft sand.

Enceladus

Enceladus
One of the “minor” moons of
the Solar System, Enceladus is
the 6th largest moon of Saturn.
Cassini has observed a water
“plume”. We believe this is a
“geyser” formed from a pocket
of liquid water under the
surface of the moon.

Enceladus
Nasa/JPL/ESA

Triton
Not a lot is known about Triton. It is the only major moon to orbit
its planet backwards. Because of this its orbit is slowly decaying,
and someday might form a ring around Neptune! Triton does
have a thin nitrogen atmosphere, in part due to cryovolcanism.
Triton was probably was a Kuiper Belt object that was captured
by Neptune.

Saturn’s
Rings
Of course the most
amazing thing about
Saturn is its rings.
These rings are made
up millions and millions
of small clumps of ice,
most about the size of a
golf ball.

This is the Encke gap
seen by Cassini right after
orbital insertion around
Saturn. Cassini was
probably less than 1000
miles from the rings when
this was taken.
NASA/JPL/Space Science Institute

NASA/JPL/Space Science Institute
Cassini actually went “through” a gap in the rings
during orbital insertion around Saturn. So we were able
to get some very close pictures of the rings.

The Rings of Saturn
The rings are made up of many
many small bands. Several
structures can be seen in the
rings, gaps, waves, spokes
Courtesy NASA/JPL-Caltech
NASA/JPL/Space Science Institute

The Rings of Saturn
Here “shepherd
moons” make
rings and gaps.
Here different colors represent different
sizes of ice particles. The blue regions
have smaller ice particles

Distortions in the F ring due
the gravity of the moon
Prometheus
171

Roche Limit
When a moon comes
within a planet’s Roche
limit the tidal forces pull
the moon apart, making
rings!

Just recently Cassini has found larger moonlets in the rings
(about 100m by 5000m in size). These could be larger
fragments of the larger moon that broke up to form the rings.

Here Cassini is looking directly at the night side of Saturn.
You can see the formation of new rings outside the Roche
limit. The outer most ring (the E ring) is formed by the water
plumes from Enceladus.
NASA/JPL/Space Science Institute

NASA/JPL/Spa
ce Science
Institute

Miller-Urey
Experiment
This showed that to
create the building
blocks of life you just
need liquid water, basic
chemicals, and a
source of energy.

Hydrothermal Vents
Proof that life can exist and
flourish without solar energy.

Life on Earth
We think it only took about 50 million years for life to develop
once there was a solid surface and oceans on Earth, but for
2.5 billion years all life was single celled.
Life changed Earth’s early atmosphere, from one with CO 2,
N2, methane, and other gasses, to the atmosphere of O 2 and
N2 that we have today.
Only about half a billion years ago did complex multi-celled
life (plants and animals) evolve.

Life Elsewhere in the Solar System
Possibly: Europa,
Mars
Longshot:
Ganymede,
Enceladus

The Drake Equation
The Drake Equation gives an estimate of the number of other
intelligent civilizations that we can “talk to”.
N = R × f p × ne × f l × f i × f t × L
R is the rate of star formation (~7 per year)
fp is the fraction of stars with planets
ne is the number of planets that are habitable
fL is the fraction of habitable planets with life
fi is the fraction of planets with life that is intelligent
ft is the fraction of intelligent life to develop technology
L is the lifetime of the technological civilization

The Drake Equation
The Drake Equation gives an estimate of the number of other
intelligent civilizations that we can “talk to”.
N = R × f p × ne × f l × f i × f t × L
R is the rate of star formation (~7 per year)
fp is the fraction of stars with planets (~1??)
ne is the number of planets that are habitable (~0.1?)
fL is the fraction of habitable planets with life (~1?)
fi is the fraction of planets with life that is intelligent (~0.1?)
ft is the fraction of intelligent life to develop technology (~0.5?)
L is the lifetime of the technological civilization (100,000 years?)
These numbers are my guesses.... you can choose your own!
3500 = 7 ×1× 0.1× 1× 0.1× 0.5 × 100000

Drake Equation
N = R × f p × ne × f l × f i × f t × L
3500 = 7 ×1× 0.1×1× 0.1× 0.5 ×100000
If there are 3500 intelligent civilizations in our galaxy then the
average distance to the nearest alien civilization is about 160
light years!!
This means we will probably never have a “conversation” with
aliens!
Our radio signals have only traveled some 70 light years.

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Gliese 581
Gliese 581 is a red dwarf about
20 light years from Earth.
Planet “c” around Gliese 581 has
a mass of about 5 times greater
than Earth’s, and has a radius
that could be around 1.5 times
larger than Earth’s.
This is the first “Earth
sized” planet that we
have discovered
around another star!

Gliese 581
Just this year astronomers
announced finding Gliese 581 e
with a mass of 1.9 Earth masses.
However it orbits very close to the
star – it has an orbital period of
just over 3 days!
Planet “c” has an orbital period of only 13 days and “d” has a
period of 83 days! It has been calculated that “d” is in the
star’s habitable zone where liquid water could exist on the
planet!

Stellar Habitable Zones