Download ASTRONOMY: THE SOLAR SYSTEM How it All Began! About 6

ASTRONOMY: THE SOLAR SYSTEM
How it All Began!
About 6 Billion Years Ago …
 A supernova Blast wave disturbs a local interstellar gas cloud.
4.5 – 4.6 Billion Years Ago …
 STELLAR FUSION AND PLANETARY ACCRETION
Nebula Hypothesis
In the Nebular Hypothesis, a cloud of gas and dust collapsed by gravity begins to spin
faster because of angular momentum conservation
Collapsing Clouds of Gas and Dust
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.).
The Spinning Nebula Flattens
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.
The collapsing, spinning nebula begins to flatten into a rotating pancake
Because of the competing forces associated with gravity, gas pressure, and rotation,
the contracting nebula begins to flatten into a spinning pancake shape with a bulge at
the center, as illustrated in the following figure.
Condensation of Protosun and Protoplanets
As the nebula collapses further, local regions begin to contract gravitationally on their
own because of instabilities in the collapsing, rotating cloud
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.
Composition of the Solar System
The Sun
 99.8% of the mass of the entire system
 74% hydrogen
 24% helium
 2% heavy metals
The Planets
 Inner Planets: Rich in Silicates and other heavy elements
 Outer Planets: Hydrogen, Helium and Methane
Asteroid Belt, Kupnier Belt and Oort Cloud
 Silicates and Ice
The Sun
 Main Sequence, Class G star
 1.4 million km in diameter
 Surface temperature = 5778 K (5505 °C; 11,000°F)
 Core temperature = 13.6 million K (15,000,000° C; 27,000,000° F)
 About 93 million km (1AU) from Earth
The Inner Planets
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Sometimes called the "terrestrial" planets because of their proximity to Earth
("Terra" in Latin) and their similarity as compact solid bodies with rocky
surfaces.
Developed from small grains of dust that collided and stuck together to form
pebbles, boulders, kilometer- and mile-sized planetesimals, and larger planetary
embryos and protoplanets)
Includes the following…
◦ Mercury
◦ Venus
◦ Earth
◦ Mars
◦ Venus, Earth and Mars lie within the “habitable zone”
◦ Such zones are bounded by the range of distances from a star for which
liquid water can exist on a planetary surface,
They formed in the inner portion of the protoplanetary disk located closer to the
developing Sun during the first 100 million years of the System's birth
It was too warm for the four developing protoplanets to agglomerate water
and more volatile ices and bulk up sufficiently in gravitational might to hold onto
the abundant but lightest gases of the Solar nebulae (hydrogen and helium) to
become "gas giants.“
◦ Although rocky (and icy protoplanets beyond the Solar System's 2-AU "ice
line") formed in the Main Asteroid Belt, the early development of Jupiter
prevented protoplanets like icy Ceres from agglomerating into larger
planetary bodies, by sweeping many into pulverizing collisions as well as
out into the Oort Cloud or beyond Sol's gravitational reach altogether.
Many astronomers now believe that the development of planetesimals into
protoplanets as large as the moon was a runaway process
The young Solar System may have developed a swarm of hundreds of Lunarmass protoplanets in as little as 100,000 years.
In a longer, succeeding phase of growth into Mars-sized protoplanets, however,
these objects interacted gravitationally over many orbits so that their initially
circular orbits became increasingly elliptical and they collided and merged into
larger bodies over tens of millions of years.
◦ Colliding at speeds up to 22,000 miles per hour(36,000 kilometers per
hour), such a collision may have stripped most of the rocky mantle
from the protoplanet that became Mercury with its iron-rich core, while a
Mars-size protoplanet struck the early Earth off-center and created a
spray of mostly mantle material that later accreted to form the Moon.
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The larger terrestrial planets, Earth and Venus, probably needed tens of millions
of years to grow to their current size through collisions with large planetary
embryos of 1,000 to 5,000 kilometers (620 to 3,100 miles).
By modeling the process of planetary accretion, astrophysicists would have
expected Mars to reach the size of the Earth at its orbital distance within the
early Sun's circum-Solar gas and dust disk. Mars, however, has only 11 percent
of Earth's mass and 53 percent of its diameter and so may have taken only two
to three million years to reach its present size.
Mars may have remained at its relatively small size by avoiding further
collisions with other larger planetary embryos.
Mercury
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MERCURY FACTS
1st planet from the Sun (.38 AU)
4878 km in diameter
Rotational period = 58.65 Earth days
◦ Possible due to the Sun’s tidal forces
1 year = 88 Earth days
◦ 1 full day – night cycle = 179 Earth days
No atmosphere
Heavily cratered surface
Liquid Iron Core
No moons
Temperatures: Daytime = 427o C
Nighttime = -173o C
Mercury’s Magnetosphere
Mercury is the only other inner planet aside from Earth that generates a
magnetic field.
The magnetic field is tilted due to the misalignments of Mercury’s geographic
and magnetic poles
Venus
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VENUS FACTS
2nd planet from the Sun (.72 AU)
12,103 km in diameter
1 rotational period = 243 Earth days
◦ Retrograde: rotates opposite direction of Earth
◦ Due possibly to abundant early planetismal collisions and tidal forces of
the Sun.
1 year = 225 Earth days
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Atmosphere
◦ 90 bars air pressure at surface (equal to 1 km depth in ocean)
◦ Major: 96.5% CO2 and 3.5% N2
Minor: SO2 , Ar, H2O, CO, He and Ne
Surface features
◦ About 900 impact craters
◦ Oldest features = 800 myo
◦ Surface folds and faults
◦ Lava flows and volcanoes
Temperature
◦ over 460 °C (860 °F)
No direct measurements as to the structure of the Venusian interior
Whether the core is now solid, partially solid, or just starting to solidify is still
under debate.
◦ The core may be similar in size to the Earth with a radius of about 3000 km
Venus is differentiated with a basaltic crust extracted from the mantle. The crust
appears to measure between 25 to 40 km and in some areas more than 50 to 60
km.
Fe and Mg – rich lava flows
Silica – rich crustal surface
No tectonic activity
No magnetic field
No moons
Earth
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EARTH FACTS
3rd planet from the Sun (1 AU)
12,756 km in diameter
1 rotational period = 24 hrs.
1 year = 365 days
Atmosphere
◦ 78% N2, 21% O2, with traces of Ar, CO2 ,H2 and O3
◦ Divided in 5 layers (top to bottom)
 Exosphere
 Thermosphere
 Mesosphere
 Stratosphere
 Troposphere
Temperature range
◦ -88°C to 58°C (- 127°F to 136°F)
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Surface features
◦ Covered by 70% water
◦ Oceans, lakes and rivers
◦ Faults and folds
◦ Canyons and mountains
◦ Abundant and diverse life
Composition
◦ Crust – rich in silicates and carbonates
◦ Mantle – Fe and Mg silicates
◦ Core - Fe and Ni
Tectonically active
◦ 15 major tectonic crustal plates
◦ Volcanoes
◦ Earthquakes
1 moon
Mars
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MARS FACTS
4TH Planet from the Sun (1.52 AU)
6794 km in diameter
1 rotational period = 24.39 hrs.
1 year = 365.25 Earth days
Atmosphere
◦ Thin atmosphere (less than 1% of Earth)
◦ 95% CO2, 3% N2, 1.6% Ar
◦ Traces of O2, H2O and CH4 (organic source?)
◦ Dust devils
◦ Seasonal dust storms
Surface Features
◦ Volcanoes: (Olympus Mons – Larges in solar system)
◦ Canyons: (Valles Marineris – Largest in solar system)
◦ Polar ice (H2O and CO2 )
◦ Impact craters
◦ Lava flows
◦ Sand dunes
◦ Stream deposits
◦ Delta deposits
◦ Lake deposits
Temperature
◦ −87 °C to −5 °C
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Composition
◦ Crust: Varies: Fe – silicate to carbonates
◦ Mantle: Fe, Mg silicates
◦ Core: Fe, S
◦ Tectonically inactive
Lacks a magnetic field
2 moons
◦ Possible captured asteroids
◦ Deimos
◦ Phobos – decaying orbit
 In 50 million years
 Form a ring around Mars
 Crash into Mars
If life exist it is probably
in the subsurface.
◦ Due to bombardment of high doses of UV radiation from the Sun through
the thin atmosphere