Transcript File

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
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 exceptions to these general rules 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 supported one model.
• This model is called the Nebular Theory.
• This Theory holds that our solar system formed
from a giant, swirling 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,
flat
disk with material
near the center
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.
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”.
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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
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 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