Transcript Origin of the Solar System ppt

Our Solar System and Its Origin
Comparative Planetology
• By studying the differences and
similarities between the planets, moons,
asteroids and comets, we can gain a
fuller understanding of the solar system
as a whole.
Side View of
Our Solar
System
The Origins of the Solar
System:
Four Challenges
1)
2)
3)
4)
Patterns of Motion
Categorizing Planets
Asteroids and Comets
Exceptions to the Rules
Challenge 1: Patterns of Motion
• All planets orbit the Sun in the same direction --counterclockwise when seen from high above the
Earth’s North Pole.
• All planetary orbits lie nearly in the same plane.
• Almost all planets travel on nearly circular orbits,
and the spacing between planetary orbits
increases with distance from the Sun according to
a fairly regular trend.
Challenge 1: Patterns of Motion - Continued
• Most planets rotate in the same direction
in which they orbit- counterclockwise when
seen from above the Earth’s North Pole –
with fairly small axial tilts (i.e. < 25o)
• Almost all moons orbit their planet in the
same direction as the planet’s rotation and
near the planet’s equatorial plane.
• The Sun rotates in the same direction in
which the planets orbit.
Challenge 2: Categorizing Planets
• Terrestrial Planets: Earth-like
planets.
• These include Mercury, Venus, Earth
and Mars.
• Jovian Planets: Jupiter-like planets.
• These include Jupiter, Saturn,
Uranus, and Neptune.
Challenge 2
• The second challenge for any theory
of solar system formation is to
explain why the inner and outer solar
system planets divide so neatly into
two classes.
• Terrestrial Planets
• Jovian Planets
Challenge 3
• In order for a theory to be complete, it must also address
the issue of Asteroids and Comets.
• Asteroids are small, rocky bodies that orbit the Sun
primarily in the asteroid belt.
• Comets are small, icy bodies that spend most of their
lives well beyond the orbit of Pluto. (Oort Cloud)
• We generally recognize them only on the rare occasions
when one visits the inner solar system.
• We know today that comets are orbiting the Sun
primarily in two broad regions.
– The Kuiper (Koy-per) belt:
(Begins in the vicinity of the orbit of Neptune ~
30AU)
– The Oort Cloud: Huge spherical region centered
on the Sun and extending perhaps half way to
nearest stars.
• The Third Challenge for any theory of solar system
formation is to explain the existence and general
properties of the large numbers of asteroids and
comets.
– Why are there so many?
– How did their existence come about?
Challenge 4:
Exceptions to the Rule
Some objects don’t fit into the general pattern:
• Mercury and Pluto have larger eccentricities.
• Pluto and Uranus are substantially tilted.
• Venus rotates backwards.
Four Major Characteristics of the Solar System
• Large bodies in the solar system have orderly
motions.
• Planets fall into two main categories:
– Small, rocky terrestrial planets.
– Large, hydrogen rich gas giants (Jovian planets).
• Several notable exceptions to these general trends
stand out:
– Planets with unusual axial tilts or surrounding
large moons.
– Moons with unusual orbits.
The Nebular Theory
• In the past few decades, a tremendous amount of
evidence has accumulated in support of one
model.
• This model is called the Nebular Theory.
• This Theory holds that our solar system formed
from a giant, swirling interstellar cloud of gas and
dust.
Nebular Model
Original Cloud
is large and
diffuse with
little
rotation
The cloud heats
up and spins
faster
and faster as
it contracts
This results in a
spinning,
flattened
disk, with mass
concentrated
near the center
What evidence is there in support of the
Nebular Theory?
Beta
Pictoris
(Hubble)
Twin Dust disks
around a binary star
system., taken by the
VLA at radio
wavelengths
Protoplanetary
disks around
stars
in the
constellation
Auriga
Protoplanetary disks around stars in the
Orion Nebula (Hubble)
Building The Planets
• Condensation: Sowing the Seeds of
Planets
– Condensation is the formation of
solid or liquid particles from a
cloud of gas.
– We refer to such solid particles as
condensates.
The Ingredients of the Solar Nebula Fell Into Four
Categories Based on Their Condensation
Temperatures:
• Metals
• Rocks
• Hydrogen compounds
• Light gases
Hot
Cool
Temperature Differences in the Solar Nebula
• Metals: Include mostly iron, nickel, aluminum
• Rocks: materials common on the surface of
the Earth. Primarily silicon based minerals.
• Hydrogen Compounds: Molecules such as
methane (CH4), ammonia (NH3), and water
(H2O) that solidify into ices below 150K.
• Light gases: (hydrogen and helium) never
condense under solar nebula conditions.
Accretion: Assembling the Planetesimals
• The process of growing by colliding
and sticking is called accretion.
• The growing objects that formed by
accretion are called planetesimals,
which means “pieces of planets”.
Early in the accretion process, there are
many Moon sized planetesimals on
crisscrossing orbits
As time passes, a few planetesimals grow
larger by accretion while others collide and
are destroyed
Only the largest planetesimals avoid being
destroyed. These bodies will become the
planets of this newly formed solar system
Nebular Capture: Making the Jovian Planets
• Large icy planetesimals of the outer solar
system act as seeds for capturing large
amounts of hydrogen and helium gas. This
is called nebular capture.
• This explains the large sizes and low
densities of the Jovian planets.
• Nebular capture also explains the
formation of the diverse satellite systems
of the jovian planets.
The Solar Wind: Clearing Away the Nebula
• The remaining gas of the solar nebula
was blown into interstellar space by the
solar wind (a flow of charged particles
ejected by the Sun in all directions.)
• The Solar wind is believed to have been
much stronger in the past than it is
today.
Leftover Planetesimals
• Origin of Asteroids and Comets:
• The strong wind from the young Sun cleared
excess gas from the solar nebula, but many
planetesimals remained scattered between
the newly formed planets.
• These leftovers became the comets and
asteroids.
The Early Bombardment:
A Rain of Rock and Ice
• The collision of a leftover planetesimal with a
planet is called an impact, and the
responsible planetesimal is called the
impactor.
• On planets with solid surfaces, impacts leave
the scars we call impact craters.
• Impacts were extremely common in the
young solar system.
The Earth, Moon and other planets were heavily
bombarded with leftover planetesimals.
Captured Moons
• Some moons have unusual orbits –
orbits in the “wrong” direction or
with large inclinations to the planet’s
equator.
• These unusual moons are probably
leftover planetesimals that were
captured into orbit around a planet.
The two moons of Mars are
probably captured satellites.
Giant Impacts and the
Formation of Our Moon.
• The largest planetesimals remaining as
the planets formed may have been as
large as Mars.
• It is believed that a glancing collision
with a Mars sized planetesimal was
reponsible for forming our Moon.
Earth Impact with Mars sized Planetesimal
• Artist’s
Conception of
the impact of a
Mars sized
object with
Earth which
caused the
formation of the
Moon.
Summary: Meeting the Challenges
• The nebular theory explains the
great majority of important facts
contained in our four challenges.
• However, planetary scientists are
still struggling with more
quantitative aspects, seeking
reasons for the exact sizes,
locations, and compositions of the
planets.
Other Planetary Systems
• How common are planetary systems?
• Observations have confirmed that protoplanetary
disks are common.
• Rapid advances in observational astronomy have
allowed us to search for actual planets around other
star systems.
• In the beginning of 1990, there was no conclusive
proof that planets existed around any star but the
Sun.
• By 2001, dozens of planet like objects have been
detected around other stars.
Doppler shifts allow for the detection of
slight motions of a star due to
perturbations caused by the orbiting
planet.
First 55 Extra-Solar Planets Discovered
Approximate
masses in terms
of the mass of
Jupiter
Closer
than the
Earth-Sun
distance
Leonid Meteor Shower – every November
Murchison meteor
A carbonaceous
chondrite which
exploded into
fragments over the
town of Murchison,
approx. 200 km north
of Melbourne in
Victoria, Australia, on
Sep. 28, 1969. About
82 kg of the
meteorite was
recovered.
Eyewitnesses arriving at the scene reported smelling
something like methanol or pyridine, an early indication
that the object might contain organic material.
Subsequent analysis by NASA scientists and a group led
by Cyril Ponnamperuma revealed the presence of 6
amino acids commonly found in protein and 12 that did
not occur in terrestrial life. All of these amino acids
appeared in both dextrorotatory (right-handed) and
laevorotatory (left-handed) forms, suggesting that they
were not the result of Earthly contamination. The
meteorite also contained hydrocarbons which appeared
abiogenic in character and was enriched with a heavy
isotope of carbon, confirming the extraterrestrial origin
of its organics. Initial studies suggested that the amino
acids in the Murchison meteorite showed no bias
between left- and right-handed forms.
However, in 1997, John R. Cronin and Sandra
Pizzarello of Arizona State University reported
finding excesses of left-handed versions of
four amino acids ranging from 7 to 9%,1 a
result confirmed independently by another
group.2 More than 70 amino acids have been
identified in Murchison altogether. To this
organic mixture, in 2001, was added a range of
polyols – organic substances closely related to
sugars such as glucose.
The End