Origin of the Solar System

Origin of the Solar System
The universe's timeline
According to the
Big Bang model,
the universe
expanded from
an extremely dense
and hot state and
continues to expand
today.
Age of universe
Based on measurements of the expansion using supernovae, measurements of
temperature fluctuations in the cosmic microwave background, and measurements of
the correlation function of galaxies, the universe has a calculated age of 13.73 ± 0.12
billion years.
Composition of the universe
spiral galaxy UGC 12158.
A pie chart indicating the proportional composition of different
energy-density components of the universe. Roughly ninetyfive percent is exotic dark matter and dark energy.
Origin of the Solar System
Solar Nebula Hypothesis
The nebular hypothesis is the most widely accepted model
explaining the formation and evolution of the Solar System
- cloud of interstellar gas and dust
produced by the earlier generations of stars
- the bulk of matter in the solar system consists of
hydrogen and helium created in Big Bang
- other chemical elements (abundant less then 0.1% of
hydrogen were formed by nuclear reaction in the interiors
of earlier generations of stars that existed between the Big Bang
and the time of origin of the Solar System 4.55 billion years ago
- Victor Safronov was one of the first to put forward a consistent
picture of how the planets formed from a disk of gas and dust around the Sun
“Evolution of the protoplanetary cloud and formation of the Earth and the planets”, 1969
M42 Orion Nebula
Contains molecular clouds where
star formation is occuring today
The Great Nebula in Orion is one of the most interesting of all astronomical nebulae known. Here 15
pictures from the Hubble Space Telescope have been merged to show the great expanse and diverse
nature of the nebula. In addition to housing a bright open cluster of stars known as the Trapezium, the
Orion Nebula contains many stellar nurseries. These nurseries contain hydrogen gas, hot young stars,
and stellar jets spewing material at high speeds. The Orion Nebula is located in the same spiral arm of
our Galaxy as is our Sun. It takes light about 1500 years to reach us from there.
M16 Eagle Nebula. The scale of the image on the left is about 1 light year. The blowup on the right
shows finger-like structures that are thought to be regions in which new stars are being formed. The tips
of these finger-like objects are about the size of our Solar System.
Forming the Solar System according to the Nebula hypothesis
Collapsing Clouds of Gas and Dust
A second- or third-generation
nebula forms from hydrogen
and helium left over from the
Big Bang, as well as from
heavier elements that were
produced by fusion reactions
in stars or during explosion of
stars.
The nebula condenses into a swirling disc,
with a central ball surrounded by rings.
A great cloud of gas and dust (called a nebula) begins to collapse because the gravitational forces that would like
to collapse it overcome the forces associated with gas pressure that would like to expand it (the initial collapse
might be triggered by a variety of perturbations-a supernova blast wave, density waves in spiral galaxies, etc.). It
is unlikely that such a nebula would be created with no angular momentum, so it is probably initially spinning
slowly. Because of conservation of angular momentum, the cloud spins faster as it contracts.
Law of Conservation of Angular Momentum
L – angular momentum
m – mass
v – speed
r – radius
During a rotation, the angular momentum L must be conserved.
If r decreases (cloud of gas collapses) then, for a constant mass m,
the speed v must increase (rotation becomes faster) in order to keep value of L constant.
The Spinning Nebula Flattens
The collapsing, spinning nebula begins to flatten
into a rotating pancake with a bulge at the center
The ball at the center grows
dense and hot enough for
fusion reactions to begin. It
becomes the Sun. Dust (solid
particles) condenses in the
rings.
p.26-27b
original artwork by Gary Hincks
Dust particles collide
and stick together,
forming planetesimals.
Condensation of protosun and protoplanets
As the nebula collapses further, instabilities in the collapsing, rotating cloud cause local regions to begin to
contract gravitationally. These local regions of condensation will become the Sun and the planets, as well
as their moons and other debris in the Solar System. While they are still condensing, the incipient Sun and
planets are called the protosun and protoplanets, respectively.
Bombardment of an embryonic planet by planetesimals. The impacts of
planetesimals on the planet’s surface deposit large enough to cause explosions,
partial melting and lava eruptions.
Gravity reshapes the protoEarth into a sphere. The
interior of the Earth separates
into a core and mantle.
p.26-27c
Forming the planets from planetesimals:
Planetesimals grow by continuous collisions.
Gradually, an irregularly shaped proto-Earth
develops. The interior heats up and becomes soft.
original artwork by Gary Hincks
Interior structures of terrestrial planets and Moon
p.26-27e
original artwork by Gary Hincks
Eventually, the atmosphere
develops from volcanic gases.
When the Earth becomes cool
enough, moisture condenses
and rains to create the oceans.
p.26-27
Life Cycle of the Sun
Events in the formation of Solar System
1.A cloud of interstellar gas and/or dust (the "solar nebula") is disturbed and collapses under its own gravity. The
disturbance could be, for example, the shock wave from a nearby supernova.
2.As the cloud collapses, it heats up and compresses in the center. It heats enough for the dust to vaporize. The initial
collapse is supposed to take less than 100,000 years.
3.The center compresses enough to become a protostar and the rest of the gas orbits/flows around it. Most of that gas
flows inward and adds to the mass of the forming star, but the gas is rotating. The centrifugal force from that prevents
some of the gas from reaching the forming star. Instead, it forms an "accretion disk" around the star. The disk radiates
away its energy and cools off.
4.First brake point. Depending on the details, the gas orbiting star/protostar may be unstable and start to compress
under its own gravity. That produces a double star. If it doesn't ...
5.The gas cools off enough for the metal, rock and (far enough from the forming star) ice to condense out into tiny
particles. The metals condense almost as soon as the accretion disk forms (4.55-4.56 billion years ago according to
isotope measurements of certain meteorites); the rock condenses a bit later (between 4.4 and 4.55 billion years ago).
6.The dust particles collide with each other and form larger particles. This goes on until the particles get to the size
of boulders or small asteroids.
7. Run away growth. Once the larger of these particles get big enough to have a nontrivial gravity, their growth
accelerates. Their gravity (even if it's very small) gives them an edge over smaller particles; it pulls in more,
smaller particles, and very quickly, the large objects have accumulated all of the solid matter close to their own
orbit. How big they get depends on their distance from the star and the density and composition of the
protoplanetary nebula. In the solar system, the theories say that this is large asteroid to lunar size in the inner solar
system, and one to fifteen times the Earth's size in the outer solar system. There would have been a big jump in size
somewhere between the current orbits of Mars and Jupiter: the energy from the Sun would have kept ice a vapor at
closer distances, so the solid, accretable matter would become much more common beyond a critical distance from
the Sun. The accretion of these "planetesimals" is believed to take a few hundred thousand to about twenty million
years, with the outermost taking the longest to form.
8.How big were those protoplanets and how quickly did they form? At about this time, about 1 million years after
the nebula cooled, the star would generate a very strong solar wind, which would sweep away all of the gas left in
the protoplanetary nebula. If a protoplanet was large enough, soon enough, its gravity would pull in the nebular
gas, and it would become a gas giant. If not, it would remain a rocky or icy body.
9.At this point, the solar system is composed only of solid, protoplanetary bodies and gas giants. The
"planetesimals" would slowly collide with each other and become more massive.
10.Eventually, after ten to a hundred million years, you end up with ten or so planets, in stable orbits, and that's a
solar system. These planets and their surfaces may be heavily modified by the last, big collisions they experience
(e.g. the largely metal composition of Mercury or the Moon).
Zones in the Solar system
1)
2)
3)
4)
5)
The terrestrial planets and moons– Mercury, Venus, Earth, Mars
Asteroid belt
The giant planets and moons– Jupiter, Saturn, Uranus, Neptune
Pluto
Comets and Kuiper Belt objects
Evidence for the Nebular Hypothesis
Because of the original angular momentum and subsequent evolution of the collapsing nebula, this
hypothesis provides a natural explanation for some basic facts about the Solar System:
1)
the orbits of the planets lie nearly in a plane (ecliptic plane) with the sun at the center
2)
the planets all revolve in the same direction
3)
the planets mostly rotate in the same direction with rotation axes nearly perpendicular to the
orbital plane.
Side view of the inner Solar System
In this figure the white portion of the
orbit is above the ecliptic plane and
the yellow portion is below.
Notice that the orbits of the
inner planets are nearly, but not quite,
in the same plane.
The orbit of Mercury, in addition
to being the most eccentric, has the
largest tilt (7 degrees) with respect to
the ecliptic plane.
Notice that Pluto's orbit is highly tilted
(17 degrees) relative to the plane of the ecliptic.
Side view of the entire Solar System
The plane of the ecliptic is well seen in this picture from the lunar
prospecting Clementine spacecraft. Clementine's camera reveals (from right
to left) the Moon lit by Earthshine, the Sun's glare rising over the Moon's
dark limb, and the planets Saturn, Mars and Mercury (the three dots at lower
left).
The inner Solar System to scale
The entire Solar System
Is Solar System still evolving?
Evolution of orbits of planets
and other bodies in the Solar System
From chaotic and unstable
to
ordered and stable
Numerous collisions were occuring during the early stages of formation of the Solar System
Origin of Moon
Origin of the Moon in a giant impact
near the end of the Earth’s formation.
Object perhaps the size of Mars collided
with Earth and threw enough matter
in the orbit to create the Moon.
Off-center collision with
a Mars-mass impactor
Simulation of 23 hours
Canup and Asphaug
(Nature, 2001)
Comet Shoemaker-Levy 9
was a comet that broke apart and collided with Jupiter in July 1994,
providing the first direct observation of an extraterrestrial collision of solar system objects
Although much more slowly the Solar System is still evolving today. Trajectories of planetary bodies are
perturbed, bringing the bodies on a collision course from time to time…
Art by ED LOPEZ
Triton's low orbit around its parent planet Neptune will result in its
destruction some 3.6 billion years in the future
Earth’s movements
As the Earth spins around its axis and orbits around the Sun, several
quasi-periodic variations occur, resulting from gravitational interactions
between the Earth, Sun and other planets. Although the curves have a
large number of sinusoidal components, a few components are dominant.
Milankovitch studied changes in the of Earth's movements (movie “Sun”).
Timescales of the changes: tens to hundreds of thousands of years
Varying orbital eccentricity
Axial tilt
Axial precession
Solar composition and age
Primordial composition of the Solar System can be deduced by analyzing
1)
Materials released from comets when they approach Sun and are warmed by its heat
2)
Primitive meteorites known as carbonaceous chondrites.
The oldest known chondrites were formed about 4.6 billions years ago as determined
by the method of radiometric dating.
The relative abundances of elements in these objects are,
except for extremely volatile elements such as H2, He, Li,
strikingly similar to abundances in the solar atmosphere (next slide).
Estimated solar system abundances of the elements, atoms per 106 Si atoms.(
Element
Abundance
10
1
H
2.66 × 10
2
He
1..9 × 109
3
Li
4
23
V
254
1.27 × 104
24
Cr
60
25
Mn
Be
1.2
26
Fe
5
B
45
27
Co
6
C
1.11 × 107
28
Ni
7
N
2.31 × 106
29
Cu
540
8
O
1.84 × 10
7
30
Zn
1260
9
F
780
31
Ga
38
32
Ge
117
33
As
6.2
Se
67
35
Br
9.2
36
Kr
41.3
37
Rb
38
Sr
39
Y
4.8
40
Zr
12
Nb
0.9
Mo
4.0
10
11
Ne 2.4 × 10
6
Na 6.0 × 10
4
12
Mg 1.06 × 10
13
Al
14
8.5 × 10
4
Si 1.00 × 10
16
S
17
Cl
5.0 × 10
6
6
5
4740
18
Ar 1.06 × 10
19
K
5
3500
20
Ca 6.25 × 10
21
Sc
31
22
Ti
2400
(a)
4
Cameron, 1981.
34
41
42
9300
9.0 × 10
5
2200
4.78 × 10
6.1
22.9
4
Iron has the most stable
nuclide, i.e. the highest
binding energy per
nucleon
Deep Impact mission, a first look inside a comet
In 2005, NASA’s Deep Impact mission created a crater in Comet Tempel 1 and enabled
to study the freshly exposed material for clues to the early formation of the solar system
Comet Tempel-1 may have been born in the region of
the solar system occupied by Uranus and Neptune
today, according to one possibility from an analysis of
the comet's debris blasted into space by NASA's Deep
Impact mission.
If correct, the observation supports a wild scenario for
the solar system's youth, where the planets Uranus and
Neptune may have traded places and scattered comets
to deep space.
Comet Tempel 1, 67 seconds after it obliterated
Deep Impact's impactor spacecraft
The sequence of eight images above depicts the development of the ejecta plume when Deep Impact's
impactor collided with comet Tempel 1 at 10:52 p.m. Pacific time, July 3, 2005. The red arrow (appearing
in both image 3 and 7) highlight shadows due to opacity of the ejecta. The yellow arrow on image 8
indicates the zone of avoidance in the up range direction. The 8 images, taken by the spacecraft's high
resolution camera, were spaced 0.84 seconds apart.
Condensation of material in the accretion disk
and resultant chemistry of the planets
Position of frost line in Solar Nebula
Position of frost line in Solar Nebula
The position of the planets in the solar nebula greatly affected
their 1. size and 2. composition. This is because of the effect of
how cold it was in the nebula (condensation sequence playing its role).
The nebula was a lot warmer close to the proto-sun. The
blue line shown in the picture shows the point at which the
temperature became cold enough for gases to become ice. At this
point and further out, beginning with the forming Jupiter, the
materials forming proto-planets began to extract from the cloud
ice, as well as rocky material and gas molecules. Retention of ice
resulted in these proto-planets becoming giant, massive planets.
The densities of planets
The masses of the planets
Mean densities of planets
(water=1)
Mercury
Venus
Earth
Mars
5.43 g/cm3
5.25
5.52
3.93
Jupiter
Saturn
Uranus
Neptune
Pluto
1.33
0.71
1.24
1.67
2.03
The size scale of Sun and planets
Fig. 1.16
W. W. Norton
Water-rich Earth
How water became so abundant on the Earth?
As a consequence of chaotic orbits in the early stages of
evolution of Solar System much water was delivered to Earth
in numerous collisions of H2O-rich asteroids with the young
Earth. H2O belongs to the least volatile compound among
volatile species such as are ammonia (NH3), methane (CH4),
nitrogen (N2), hydrogen (H2), helium (He).
One day, 65 million years ago, a large asteroid, about 10 km across, approached the Earth.
Striking just north of the Yucatan peninsula, it formed a 180-km-wide crater known as
Chicxulub. One likely consequence of this catastrophic event was the eradication of much
of the flora and fauna then existing on Earth - probably including the dinosaurs.
Literature and study material
The presented lecture can be downloaded from the Studentportalen (pdf-format file).
Weblinks
http://sse.jpl.nasa.gov/
http://www.nasa.gov
http://en.wikipedia.org
Additional study material
The New Solar System
Eds: J.K. Beatty, C.C. Petersen, A.Chaikin
4th edition, Cambridge University Press, 1999
The Story of the Solar System
by Mark A. Garlick
Cambridge University Press 2002
Physics and Chemistry of the Solar System
J.S. Lewis, Academic Press, 1997
Planeter, Stjärnor, Galaxer
Claes-Ingvar Lagerkvist och Kerstin Loden
Liber AB, 1994
Från Big Bang till livet på jorden
Clas Blomberg, Ingemar Hedström, K.G. Karlsson
Raben Prisma, 1997
Encyclopedia of Planetary Sciences
Edited by J.H. Shirley and R.H. Fairbridge
Chapman & Hall, 1997
Examples of exam questions from previous years:
What is the origin of large differences in chemical composition between the terrestrial and Jovian planets?
Describe briefly origin of the Solar System according to Nebula hypothesis. Is the Solar System still evolving?
Which are the main parameters controlling the condensation sequence of elements and minerals in the protoplanetary disc
during the early stages of formation of the Solar System?
Contact information:
Peter Lazor
Peter.Lazor@geo.uu.se
tel. 018 - 471 2556