formation of the solar system
DESCRIPTION
Formation of the Solar System. Uncovering the origin of the Solar system Early days of the formation Building the planets and other stuff Other planetary systems. Studying planets as worlds and compare them with each other is called comparative planetology. Comparative Planetology. - PowerPoint PPT PresentationTRANSCRIPT
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Formation of the Solar System• Uncovering the origin of the Solar system
• Early days of the formation
• Building the planets and other stuff
• Other planetary systems
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Comparative Planetology• Studying planets as worlds and compare them
with each other is called comparative planetology
• Planetology is applied to any noticeably large object in the system (planets, moons, asteroids, comets)
To start we need to seek clues to the origin of the Solar system
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Four Challenges1. Pattern of Motion• All planets orbit the Sun in the same direction
(counterclockwise as seen from the Earth’s North Pole) • Planet orbits are nearly circular and co-planarPlanets rotate in the same direction which they orbitAlmost all moons orbit their planets in the direction of the planet rotationThe Sun rotates in the direction planets orbit it
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Four Challenges2. Different types of planetsTwo distinct groups of planets:Terrestrial planets (Mercury, Venus, Earth, Mars)Small, rocky, abundant in metals, few moons
Jovian planets (Jupiter, Saturn, Uranus, Neptune)Large, gaseous (made of hydrogen and its compounds), no solid surfaces, have rings, a lot of moons (made of low-density ices and rocks)
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Four Challenges3. Asteroids and Comets
Asteroids are small, rocky bodies that orbit the Sun mostly between Mars and Jupiter (the asteroid belt)Almost 10,000 asteroids have been discovered
Comets are small and icy bodies that spend most of their lives beyond the orbit of PlutoThey occupy 2 regions: Kuiper belt and Oort cloud
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Four Challenges
4. Exception to the Rules
• Mercury has larger orbital eccentricities• Uranus has tilted rotational axes• Venus rotates backwards (clockwise)• Earth has a large moon
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The Nebular Theory
The Solar system was formed from a giant, swirling interstellar cloud of gas and dust
A cloud is called nebula - nebular hypothesis
The collapsed piece of cloud that formed our own solar system is called the solar nebula
The hypothesis was originally suggested by Immanuel Kant (1755) and Pierre-Simon Laplas (~1790)
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Collapse of the Solar NebulaThree important processes gave form to our system,
when it collapsed to a diameter of 200 A.U.
1. The temperature increased as it collapsed2. The rotation rate increased3. The nebula flattened into a disk (protoplanetary
disk)
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9
Formation of Solar System Summarized
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Building the PlanetsInitial composition: 98% hydrogen and helium, and 2% heavier elements (carbon, nitrogen, oxygen, silicon, iron)
Condensation: the formation of solid or liquid particles from a cloud of gas
Different kinds of planets and satellites were formed out of different condensates
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Ingredients of the Solar SystemMetals : iron, nickel, aluminum, etc.Condense into solid form at 1000 – 1600 K0.2% of the solar nebula’s massRocks : primarily silicon-based mineralsCondense at 500 – 1300 K, 0.4% of the massHydrogen compounds : methane (CH4), ammonia (HN3), water (H2O)Condense into ices below 150 K, 1.4% of the mass
Light gases: hydrogen and heliumNever condense in solar nebula; 98% of the mass
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Condensation
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AccretionAccretion is growing by colliding and stickingThe growing objects formed by accretion – planetesimals (pieces of planets)
Small planetesimals came in a variety of shapes, reflected in many small asteroidsLarge planetesimals (>100 km across) became spherical due to the force of gravity
Inner solar system: only rocks and metals condensed and only small bodies formed
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Nebular CaptureNebular capture – growth of icy planetesimals by capturing larger amounts of hydrogen and heliumIt led to the formation of the Jovian planets
Numerous moons were formed by the same processes that formed the protoplanetary diskCondensation and accretion created mini solar systems around each Jovian planet
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The Solar WindSolar wind is a flow of charged particles ejected by the Sun in all directionsIt was stronger when the Sun was young
The wind swept out a lot of remaining gas and interrupted the cooling of the nebula
If the wind were weak, the ices could have condensed in the inner solar system
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Leftover PlanetesimalsPlanetesimals remained from the clearing became comets and asteroids
They were tugged by the strong gravity of the jovian planets and got more elliptical orbits
Rocky leftovers became asteroidsIcy leftovers became comets
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Planetary Evolution - Geological
Internal heating leads to geological activity: volcanism, tectonics
As core cools and solidifies, activity slows, and eventually stops (Moon)
Earth and Venus are large enough to be active
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Planet Activity
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Planetary Evolution - Atmosphere
Atmospheres are formed by:- gases escaping from interior- impacts of comets (volatile-rich debris)
Fate of water depends on temperature (distance from the Sun)
Atmospheres changed chemically over time
Life on Earth substantially changed the atmosphere
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Other Planetary Systems
Over 100 extrasolar planets have been discovered since 1995 The Extrasolar Planet Encyclopedia
Stars are too far away from the Sun, and direct imaging cannot detect planets near them
Current strategy involves watching for the small gravitational tag the planet exerts on its star
The tag can be detected using the Doppler effect
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Extrasolar Planets in the Sky
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Planet Transits
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The Nature of Extrasolar PlanetsThe discovery of extrasolar planets gives us an opportunity to test the solar system formation theory
Most of the discovered planets are different from those of our systemThey are mostly Jupiter-size and located closer to their stars But: possible planet migration discovered planets are exceptions
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Summary
All the planets were formed from the same cloud of dust and gas
Chance events may have played a large role in the formation and evolution of individual planets
Planet-forming processes are apparently universal