Download Solar System Formation

Formation of Solar System
• Introduction
• Origin of Solar System
• Formation of the planets
• Planets and their orbit
• Extrasolar planets
Introduction
• Planetary astronomy is the study of our solar
system
• To understand our own solar system and thus
explore the possibility of life in outer space
• A few known approved theories of the
formation and evolution of solar system
Origin of Solar System
There are a few theories about how the solar system
evolved. These can generally be divided into 2 broad
categories:
• That the solar system is purely an accidental catastrophic
event
• Eg. Near collision between the Sun and another star
• That the solar system evolved in a natural, noncatastrophic way
• Eg. Birth of a star
Origin of Solar System
Encounter Theories
• First conceived in 1745 by French naturalist Georges Buffon
(1707-1788)
• Proposed that material ripped off from the Sun by collision
with a comet had condensed into the planets
• Giant eruptions were pulled off the Sun by the gravitational
attraction of a passing star.
• Harold Jeffreys (b. 1891) and James Jeans (1877-1946),
theorized that a cigar-shaped gaseous filament was pulled from
the Sun by the sideswiping action of a passing star. The middle
section condensed into the Jovian planets, and the ends
condensed into the smaller planets.
Origin of Solar System
Nebular Hypothesis
• Solar System formed out of a huge rotating gaseous nebula
slowly contracting and condensing
• 2 origins of nebula – nova / supernova
• Nebula origin still under debate
• As the large, slowly rotating solar nebula of hot gaseous
matter contracted, it rotated faster and faster, flattening into
an equatorial ring
• Gravity shrinks the solar nebula
• Given angular momentum must remain constant unless
energy is taken out of rotation and put into some other
form
•Therefore rotational velocity increases as radius
decreases
Origin of Solar System
Nebular Hypothesis
Origin of Solar System
Nebular Hypothesis
• When centrifugal force on the outer rotating edge of
the solar nebula exceeds inward gravitational force of the
nebular mass, a ring of gaseous matter will split off,
eventually coalescing into a planet
• Splitting process repeats itself, making concentric rings
that formed into planets
• Central portion condensed to become the Sun
Origin of Solar System
Nebular Hypothesis
Origin of Solar System
Nebular Hypothesis - Inconsistencies
• While 99 percent of the Solar System mass resides
in the Sun, 99 percent of the angular momentum of
the system resides in the planets' orbital and
rotational motions
• A hot gaseous ring of the type postulated would
disperse into space and not pull itself together
gravitationally to form a planet.
Origin of Solar System
Protoplanet Theory, the Solar Nebula
Origin of Solar System
Protoplanet Theory, the Solar Nebula
• Improvement of nebular hypothesis
• Starts with a nebula fragmented from interstellar cloud
• Composed mainly of hydrogen and helium
• Trace amounts of other elements
• The central region, being more dense, collapsed more
rapidly than its outlying parts.
• Known as: Solar nebula
• The original interstellar cloud must have been rotating,
and as it fragmented, rotation was imparted to each
fragment
Origin of Solar System
Protoplanet Theory, the Solar Nebula
• As the solar nebula contracted, it rotated more
rapidly, conserving angular momentum
• The solar nebula grew by accretion as material
continued to fall inward from its surroundings
• Large-scale turbulence from gravitational
instabilities breaks the thin disk into rings, each
containing many small particles. These particles
gradually built up into larger bodies by some
combination of adhesive forces
Origin of Solar System
Protoplanet Theory, the Solar Nebula
• As the central portion of the solar nebula contracted,
the temperature rose to around 2000 K
• Vaporises all compounds in the dust except metallic
and silicate minerals in the inner portion of the disk
• Planets that formed close to the young Sun, such as
the Terrestrial planets, would be expected to contain less
of the volatile icy and gaseous materials and thus be
richer in the rocky materials
Formation of the planets
Nearer to the Sun, temperatures are very high, so that they allow
only rock and other minerals can condense. Thus, the formation of
rocky planets: Mercury, Venus, Earth, Mars.
The asteroid belt originally was theorized to be a planet, which was
hit by a large comet / other large bodies, and broke into the million
pieces orbiting the Sun.
From about Jupiter outward, ammonia and methane will be formed
due to very cold temperatures, giving those distant planets a mixed
composition of water, ammonia, and methane ice impregnated with
a small amount of rocky matter.
There is much debate about whether Pluto is a planet, even. As its
composition is mostly ice, it could even be a comet captured by the
Sun’s gravity.
Formation of the planets
Formation of the planets
Formation of the planets
Planets and their orbit
Planets and their orbit
• All orbits have at least a small tilt in their orbit path
• Exception: Mercury, Pluto
• All orbits are only nearly circular
• Exception: Mercury and Pluto have highly elliptic orbits
• All planets rotate west-east, same as the Sun’s rotation
• Exception: Venus, Uranus, Pluto
• All planets revolve around the Sun west-east, same as the Sun’s
rotation
• Terrestrial planets have high mean densities and relatively thin
or no atmospheres, rotate slowly, and possess few or no satellites
•The giant planets have low mean densities, relatively thick
atmospheres, and many satellites, and they rotate rapidly
Planets and their orbit
Titus-Bode’s Law
• Suppose you write out the multiples of 3:
•0, 3, 6, 9, 12, 15, 18
• Add 4 to each number:
•4, 7, 10, 13, 16, 19, 22
• Divide each number by 10:
•0.4, 0.7, 1, 1.3, 1.6, 1.9, 2.2
• This series of numbers give the distance (AU) of each planet
from the Sun!
• Likely due to the way the Solar System evolved, the numbers
give a very close estimate to the distances of the planets and
the Sun
Planets and their orbit
Titus-Bode’s Law: Inconsistencies
• The inconsistency of Titus-Bode’s law occurs from Saturn,
mostly after Uranus
• Probably due to the fact that the outer planets were formed
from rings broken away from the solar nebula
• Another theory for the inconsistency: the warping of space
due to the masses of the planets (Theory of Relativity)
Extrasolar Planets
• In just the last few years, astronomers have discovered large,
cool, dust envelopes around infrared stars in the interstellar
clouds of the Milky Way. They may be in the early stages of
nebular condensation of the protoplanet theory
• Very recent findings: Vega (in Lyrae), Fomalhaut (in Piscis
Austrinus), Epsilon Eridani (in Eridanus), and Beta Pictoris (in
Pictor) and about eight other Sunlike stars
• Ground-based discoveries of circumstellar disks
around three other stars
• The disk surrounding Vega has a radius of some 80 to 90
AU (about twice Pluto's distance from the Sun)
Extrasolar Planets
• Although such observation is neither the same as finding
evidence for planetlike bodies, nor that planets will eventually
form around these stars, it does lend support to the contention
that stellar nebulae, similar to the solar nebula in the
protoplanet hypothesis, form around other stars in our Galaxy
as a natural part of the processes responsible for the birth of
stars
• Hence other ‘Solar Systems’ probably exist somewhere out in
the distant reaches of space.