Lecture 4 Origin Of The Solar System & Earth-Moon System PDF

Lecture 3: The origin of the Solar System Basic observations Solar system formation Types of planet Meteorites The composition of the earth Where did the moon come from?  Basic Observations-1 All planets (except Pluto – dwarf planet) revolve a...

Lecture 3: The origin of the Solar System Basic observations Solar system formation Types of planet Meteorites The composition of the earth Where did the moon come from?  Basic Observations-1 All planets (except Pluto – dwarf planet) revolve around the sun in the same plane – Plane of the ecliptic  Basic Observations-2 All planets (except Venus and Uranus) and most moons rotate anticlockwise (on their axis of rotation) – When viewed from a point above earth’s north pole  Basic Observations-3 There are two distinctly different types of planet – Rocky (Terrestrial) planets – Gaseous (Jovian) planets Separated by an asteroid belt Most, though not all, NASA planets have at least one satellite  Basic Observations-4 Sun spins at the center – Rotational period is 25.5 days Sun is ~ 99.86 % of the total solar system mass – 92.1 % hydrogen, 7.8 % helium, all other elements 0.1% NASA Temperature at the suns core is 15,000,000° C Pressure at core – 340 billion atmospheres  Solar System Formation Theory -1 Solar system formed from collapse of interstellar material Gravitational collapse gives a flat disk that spins CCW with ~ 98% of the material concentrated at the center Esahubble.org  Solar System Formation Theory -2 Rotation and collapse led to the formation of an embryonic sun Local turbulence in the outer material creates small instabilities Instabilities grow to form protoplanets Protoplanets sweep up material in their path and grow https://phys.org/news/2012-01-stellar- embryos.html The protoplanetary disk around the young star, HL Tauri, as photographed by ALMA. The gaps in the disk indicate the presence of new planets, while spectroscopic measurements reveal a large number and diversity of organic, carbon-containing compounds. ALMA (ESO/NAOJ/NRAO) © 2011 Pearson Education, Inc.  Solar System Formation Theory -3 https://nineplanets.org/questions/how-big-is-the-sun/ Continued collapse at centre leads to heating – Interior of proto-sun reaches several million Kelvin – Sun ignites and fusion begins This happened ~ 5 – 4.6 billion years ago – Planetesimals formed from the protoplanets  The early solar system was crowded Cc = carbonaceous chondrite – a Burkhardt et al 2021 type of meteorite.  Solar System Formation Theory-4 ~ 4.6 Ga – Planet formation mostly complete Planets are initially homogeneous? – Planets begin process of internal differentiation Dasgupta and Grewal 2019  A Major Problem! The solar nebula hypothesis makes an incorrect prediction – The sun should spin very rapidly at the centre of the solar system (with a rotation period of ~ 2 days) Based on the law of conservation of angular momentum BUT its rotation period is 25.5 days Is the solar nebula hypothesis wrong?  A Simple Solution The sun gives off a constant stream of charged particles – The solar wind Interaction of these particles with the sun’s magnetic field cause magnetic braking – i.e.. this interaction has slowed the rate of rotation over time  What Types of Planet Formed? Dense, rocky inner planets – Mercury – Venus – Earth – Mars NASA Did not have a strong enough gravitational field to hold on to light gases like H and He – Temperature too high in the inner solar system to allow ices and gases to condense  Mercury Orbit: 57,910,000 km Diameter: 4,880 km Mass: 3.30 x 1023 kg One Mercury day is 50 earth days (spins very slowly on its axis) Surface temperature ranges from 430 C to minus 180 C NASA No atmosphere  Venus NASA Orbit: 108,200,000 km Diameter: 12,103.6 km Mass: 4.869e24 kg Slow and retrograde Surface temperature is ~ rotation (on axis) 475 C – Opposite to that of earth A day on Venus is 243 earth days – longer than a Venusian year!  Earth Has a dense iron-rich core Has a mantle that is dense compared to the crust Has active volcanism Has liquid water Has an oxygen-rich NASA atmosphere  Mars orbit: 227,940,000 km diameter: 6,794 km mass: 6.4219e23 kg Home to the largest volcano in the solar system – Olympus Mons – 24 km high – 500 km diameter A Martian day (24.6 hours) is – Base is rimmed by a cliff 6 similar in length to an earth day km high! – The volcano appears to be extinct Temperatures range from 20 C to -153 C  The Jovian Planets Low density, gas-rich Separated from the Terrestrial Planets by the asteroid belt – Planetesimals that did not accrete further Jupiter Saturn Uranus Neptune Jupiter orbit: 778,330,000 km diameter: 142,984 km (equatorial) mass: 1.900e27 kg – About 5 times more massive than ALL the other planets combined! 75% H, 25% He Great red spot is a very long-lasting storm (at least 300 years) – A storm bigger than earth! https://webb.nasa.gov/  Saturn orbit: 1,429,400,000 km diameter: 120,536 km (equatorial) mass: 5.68e26 kg Low density – less than the density of water! NASA  Uranus (Yor-a-nus – pronunciation is important!) orbit: 2,870,990,000 km diameter: 51,118 km (equatorial) mass: 8.683e25 kg Pronounced Yoor A nus Axis of rotation parallel to plane of ecliptic – Most other planets axis is NASA at a high angle  Neptune orbit: 4,504,000,000 km diameter: 49,532 km (equatorial) mass: 1.0247e26 kg Discovered because it disturbs orbit of Uranus Equatorial winds reach speeds of up to 2000 km/h NASA  Meteorites – bits of early planetesimals – originate in the asteroid belt Extraterrestrial material that survives the fall through the earth's atmosphere Iron meteorite, A. Alden 2000 Types of Meteorite Iron – Fe-Ni alloy Stony iron (pallasite) – Fe-Ni alloy with silicates Stony – Chondrites – Achondrites All ~ 4.6 Ga old  What do Meteorites Tell Us? Evidence of differentiation of originally homogeneous planetary bodies 486958 Arrokoth – Kuiper Belt object Kuiper belt is icy and rock objects beyond Neptune NASA  What is the composition of the earth? NASA How could we figure out what earth is made of? What things do we know?  The sun is the clue! 99.86 % of the total solar system mass – 92.1 % hydrogen, 7.8 % helium, all other elements 0.1% The suns mass is 336,000 times that of earth What else could we use? Carnegie Earth and Planets Lab Compare the sun and chondrites Noble gases & H have low abundance in chondrites compared to the sun McDonough 2016  Carbonaceous chondrites This type of meteorite closely resembles the composition of the sun (minus H and the noble gases) A good analogue for the material that formed the planets We can test the chondrite hypothesis © 2011 Pearson Education, Inc.  Composition of Bulk Silicate Earth (BSE) (=crust + mantle) Earth differentiated into crust, mantle, outer core and inner core relatively quickly (within 30 million years of formation) The core was formed by molten iron droplets falling toward the centre of mass Core formation released a lot of heat – Melted much of the early earth – A MAGMA OCEAN  Luna NASA  Luna ¼ diameter of earth Density lower than earth – 3.3 g/cm3 – Dry – 4.6 Ga Dark Mare basins – basaltic Light, anorthositic highlands NASA Many impact craters – Many more than on earth  Origin of the Moon Various ideas – Capture from an independent orbit – Formation with earth as a two-body system – Break away during accretion – Collision of early earth with a Mars-sized impactor  The Impactor Hypothesis Object ~ same size as Mars hit earth ~ 4.6-4.4 Ga Ejected material that became the moon Earth “assimilated” the impactor  Summary Nebula hypothesis explains observed features of the solar system 2 different types of planet Earth formed as a homogeneous body and differentiated later Earth’s composition is the same as that of chondrite meteorites Moon originated via impact with a Mars-sized object