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ASTR 330: The Solar System

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Title: ASTR 330: The Solar System


1
ASTR 330 The Solar System
  • Lecture 10.5
  • Review 1
  • for
  • Mid-Term Exam 1

Dr Conor Nixon Fall 06
2
ASTR 330 The Solar System
  • Review 1 What have we learned?
  • Lecture 1 Introduction to course dates, times,
    advice, rules etc.
  • Lecture 2 Our place in space planetary motion,
    eclipses.
  • Lecture 3 The Sun nuclear energy, solar lines,
    solar activity.
  • Lecture 4 The planets densities, atmospheres,
    spectroscopy.
  • Lecture 5 Spectral windows, albedos,
    telescopes, future technology.
  • Lecture 6 Solar System Formation nebula
    collapse, planetesimals.
  • Lecture 7 8 Meteorites. Types, radioactivity,
    half-life.
  • Lecture 9 Asteroids
  • Lecture 10 Comets

Dr Conor Nixon Fall 06
3
ASTR 330 The Solar System
  • Lecture 2 History and Perspective
  • Early ideas about the planets wandering
    stars.
  • The ecliptic path of the Sun across the sky,
    through the zodiac.
  • The seasons equinoxes, solstices.
  • Phases of the Moon, and what causes them
    eclipses.
  • Geocentric universe Aristotle.
  • Retrograde motion of the planets epicycles,
    Ptolemy.
  • Heliocentric universe Copernicus.

Dr Conor Nixon Fall 06
Picture credit wikipedia.org
4
ASTR 330 The Solar System
  • Lecture 2 Eclipses
  • What is a total solar eclipse?
  • Terminology
  • Umbra and penumbra
  • Totality
  • Baileys beads
  • Diamond ring
  • What is a lunar eclipse?

Dr Conor Nixon Fall 06
5
ASTR 330 The Solar System
  • Lecture 2 Laws of Planetary Motion
  • Keplers three laws of planetary motion
  • Law of Orbits Each planet moves in an
    elliptical orbit about the sun, with the Sun at
    one focus of the ellipse.
  • Law of Areas An imaginary line connecting the
    Sun with a planet sweeps out equal areas in equal
    times as the planet moves about the sun.
  • The Law of Periods The square of the period of
    any planet is proportional to the cube of the
    semi-major axis of orbit. T2 K a3
  • Galileos discoveries.
  • Newtons ideas on gravity
  • inverse square law of universal gravitation.
  • Escape velocity.

Dr Conor Nixon Fall 06
6
ASTR 330 The Solar System
  • Lecture 3 Definitions
  • Basic definitions parallax, Kelvin temperature
    scale (celsius 273).
  • Matter
  • Atoms and elements.
  • Atomic structure the nucleus protons and
    neutrons electrons.
  • Hydrogen and Helium.
  • Molecules and compounds.
  • Light photons, waves and particles, speed of
    light, mass of light.
  • EM spectrum types of EM radiation, from Radio
    to Gamma.

Dr Conor Nixon Fall 06
7
ASTR 330 The Solar System
  • Lecture 3 The Sun
  • Parts of the Sun
  • Core where nuclear fusion occurs temperature
    15 million K. Energy is released as gamma
    radiation.
  • Radiation zone the next layer of the Sun out
    from the core gamma ray photons are repeatedly
    absorbed and re-emitted.
  • Convection zone the level immediately below the
    visible surface globs of solar liquid rise and
    fall by convection, transporting energy.
  • Photosphere the visible surface of the Sun
    5800 K.
  • Chromosphere the layer immediately above the
    photosphere visible during eclipses as a pink
    color.
  • Corona the very outer part of the Sun, merging
    with the solar wind. Very hot 4 million K. Gas in
    ionized.

Dr Conor Nixon Fall 06
8
ASTR 330 The Solar System
  • Lecture 3 Solar Lifetime Activity
  • The Sun consumes 4x106 tons of matter/second,
    converting H to He with a small fraction lost to
    pure energy. This is the Suns power source.
  • Einsteins formula E mc2 gives the relation
    between a small amount of mass and a large amount
    of energy. The fuel source will last an estimated
    10 billion years or more.
  • The Sun exhibits several types of activity
  • Sunspots dark patches on the photosphere,
    which are in fact only 1000 K cooler than the
    rest of the photosphere. Caused by material
    trapped in magnetic fields. 11-year cycle.
    Migrate to equator.
  • Flares huge eruptions from the surface,
    associated with the breaking of magnetic field
    lines. Energy is released from radio to X-ray.
  • CMEs huge ejections of matter from the corona
    into the solar wind, which are related to solar
    flares.

Dr Conor Nixon Fall 06
9
ASTR 330 The Solar System
  • Lecture 4 The Planets
  • Sizes and densities we categorize the planets
    into 3 groups
  • Terrestrial small size, high density Mercury,
    Venus, Earth, Moon, Mars.
  • Giant large size, low density Jupiter, Saturn,
    Neptune, Uranus.
  • Icy/KBO small size, low density Pluto and
    Charon, KBOs.
  • Composition clues
  • Mercury is same density as Earth, should be less
    (smaller gravity) if same protosolar proportions
    of the elements.
  • Giant planets are less dense than Earth, should
    be more (more gravity).
  • We solve this riddle by concluding that planets
    have different compositions. Closer to the sun,
    more heavy elements.

Dr Conor Nixon Fall 06
10
ASTR 330 The Solar System
  • Lecture 4 Forms of Matter
  • For the planets, it is sometimes useful to think
    of four principle components gas, ice, rock and
    metal.
  • Rocks and minerals
  • A rock is an assembly of one or (usually) more
    different minerals.
  • Minerals may be elemental (e.g. Gold, Graphite)
    or compound (SiO2).
  • Rock types igneous (e.g. basalt), sedimentary
    (e.g. limestone), metamorphic (e.g. marble).
  • Atmospheres ways for a planet to acquire an
    atmosphere
  • Direct capture from original solar nebula
    (priordial or primary).
  • Outgassed from rocks after differentiation
    (secondary).
  • From later cometary impacts (secondary).

Dr Conor Nixon Fall 06
11
ASTR 330 The Solar System
  • Lecture 4 Atmospheres
  • Ways to lose an atmosphere
  • Thermal escape from exosphere the thermal
    energy of the molecule is enough to surpass the
    escape velocity of the planet.
  • Impacts comet or asteroid impacts may blast
    atmosphere into space.
  • Ablation by solar wind particles.
  • What affects which molecules escape? (i) mass of
    planet (ii) mass of molecule (iii) temperature.

Dr Conor Nixon Fall 06
12
ASTR 330 The Solar System
  • Lecture 5 Planetary Astronomy
  • Remote sensing vs in situ investigations.
  • Spectroscopy visible (solar) and infrared
    (planetary).
  • Spectral windows absorption and transmission in
    the Earths atmosphere.
  • Meaning of albedo percentage of light reflected.
  • Infrared spectral lines give information on
  • Temperature
  • Composition
  • Pressure

Dr Conor Nixon Fall 06
13
ASTR 330 The Solar System
  • Lecture 5 Telescopes
  • Telescopes
  • Size - affects both spatial resolution, and
    amount of light collected, (or faintness of
    objects which can be detected).
  • Sites - high and dry sites are best Antartica,
    Atacama desert in Chile, Mauna Kea in Hawaii,
    space!
  • Future techniques and technology
  • Segmented giant mirrors (e.g. Keck I and II).
  • Adaptive optics, to correct for atmospheric
    twinkling.
  • Optical interferometry, to improve spatial
    resolution dramtically without having to build an
    impractically large single mirror.
  • Space telescopes - best seeing of all sites.

Dr Conor Nixon Fall 06
14
ASTR 330 The Solar System
  • Lecture 6 Solar System Formation
  • Facts we can use composition
  • the Sun is mostly H and He, most of the mass is
    in the Sun, therefore the nebula was mostly H and
    He.
  • The inner planets do not now have much in the way
    of volatiles probably never had much.
  • Other facts orbits and rotations
  • Planets mostly orbit in the same plane,
    near-circular orbits.
  • Planets orbit Sun in same direction.
  • Sun rotates in same direction as planets orbit.
  • Nebular theory of Laplace.

Dr Conor Nixon Fall 06
15
ASTR 330 The Solar System
Figure Universities Corp. For Atmospheric
Research (UCAR)
Dr Conor Nixon Fall 06
16
ASTR 330 The Solar System
  • Planetesimals to Planets, Proto-sun to Sun

Picture credit James Schimbert, U. Oregon, Eugene
Dr Conor Nixon Fall 06
Picture NASA
17
ASTR 330 The Solar System
Picture credit NASA GSFC
  • Left-overs asteroids, comets, EKOs/KBOs

Dr Conor Nixon Fall 06
Picture Johns Hopkins University
Graphic SWRI
18
ASTR 330 The Solar System
  • Lecture 7 Meteorites
  • Major mineralogical types (1) Stony (2) Iron
    (3) Stony-Iron.
  • Types by origin/history (1) Primitive
    (chondrite) (2) Differentiated (achondrite) (3)
    Breccias.
  • Primitive meteorites are all stones either (i)
    carbonaceous, or (ii) other stones.
  • Differentiated meteorites can be any of the
    mineralogical types.
  • Breccias are typically crustal material from
    asteroids or planets. May be primitive or
    differentiated.
  • Types by landing/detection (1) Falls (2) Finds.
  • Finds have a skewed distribution towards iron or
    stony-iron meteorites.

Dr Conor Nixon Fall 06
19
ASTR 330 The Solar System
  • Lecture 7 Finding Meteorites
  • Famous meteorite falls include
  • LAigle Fall (1803, France) the fall which
    first drew scientific attention to meteorites.
  • Allende Fall (1969, Mexico) the first big fall
    since the space race began. Dated to be very old
    (4.56 Gyr).
  • Murchison Fall (1969, Australia) a large fall
    of carbonaceous chondrite material, in which was
    found organics, inc. amino acids.
  • The Antarctic is a very happy hunting ground for
    meteorites, not only because they are easily
    spotted on the ice, but also because movements of
    the ice sheets tend to concentrate meteorites
    against natural barriers.

Dr Conor Nixon Fall 06
20
ASTR 330 The Solar System
  • Lecture 7 Primitives etc
  • We can determine meteorite origins by
    photographing their path across the sky from
    several different locations, and calculating the
    trajectory. E.g. Peekskill meteorite. They turn
    out to be from the main asteroid belt.
  • Primitive meteorites are old (4.5 Gyrs) with
    chondrules, possibly iron grains (H, L, LL) and
    quite often are breccias.
  • Carbonaceous chondrites are a special class of
    primitive stones, which are less dense, contain
    more volatiles and carbon.
  • Tagish Lake and Murchison are famous C.C.
    meteorites, which have been found to contain
    amino acids.
  • We know these molecules are from space by their
    chirality.
  • IPD or Brownlee particles come from comets.

Dr Conor Nixon Fall 06
21
ASTR 330 The Solar System
  • Lecture 8 Differentiated Meteorites
  • Differentiated meteorites lack chondrites hence
    are called achondrites.
  • Iron meteorites contain up to 10 nickel. When
    polished they show a crisscross Widmanstatten
    pattern due to slow cooling (below right).
  • These meteorites come from bodies (typically
    asteroids) which have undergone differentiation
    a fractional separation under heat and gravity.

Dr Conor Nixon Fall 06
Graphic SaharaMet, RR Pellison Photo NEMS
22
ASTR 330 The Solar System
  • Lecture 8 Stony-Irons, Basalts
  • Stony-iron meteorites are thought to come from
    the boundary layer between the iron core and
    stony mantle of differentiated parent bodies.
  • Stony-irons can be dated due to the their
    silicate (stony) component, and hence an age for
    similar iron meteorites can be determined.
  • Ages for differentiated bodies are 4.4 to 4.5
    Gyr, not much younger than the solar system
    hence differentiation took place early on.
  • Eucrites are meteorites which have been found to
    come from the crust of the asteroid Vesta.
  • Basalts tend to be lighter rocks from the
    asteroid crust. Some basalts however have been
    determined to some from Mars.

Dr Conor Nixon Fall 06
23
ASTR 330 The Solar System
  • Lecture 8 Radioactivity
  • Radioactivity (mostly) refers to the process of
    nuclear transformation, from one unstable
    parent isotope to a daughter isotope which is
    usually more stable.
  • Alpha decay occurs when a helium nucleus is
    emitted, moving the nucleus 2 steps up the
    periodic table.
  • Beta decay takes place when a neutron is
    transformed into a proton and an electron, moving
    the nucleus 1 step down the period table.
  • Gamma radioactivity is not an isotope
    transformation at all, rather the emission of a
    high-energy EM photon by the nucleus.

Dr Conor Nixon Fall 06
Picture www.impcas.ac.cn
24
ASTR 330 The Solar System
  • Lecture 8 Dating Meteorites
  • Radioactive dating uses the observation that the
    parent to daughter nuclear ratio decreases over
    time. By measuring the ratio in a sample, and
    using a sister isotope to estimate the original
    amount of the daughter product, we can estimate
    the age of a sample.
  • The half-life of a radioactive isotope is the
    time it takes for half of the parent nuclei to
    spontaneously decay to the daughter product.
  • The solidification age is the time since the
    sample was last molten.
  • The gas retention age is the time since the
    sample was last mechanically disturbed, e.g. by a
    shock or impact.

Dr Conor Nixon Fall 06
Picture Univ. of South Carolina/CSE
25
ASTR 330 The Solar System
  • Lecture 9 Asteroids
  • First asteroid discovered in 1801 Ceres (still
    the largest) in the gap region between the
    orbits of Mars and Jupiter.
  • Missing planet found but Juno, Pallas and Vesta
    detected soon after. Exploded planet?
  • Asteroid population follows a 1/D2 population
    (number decreases with increasing size) rather
    than the expected 1/D3 population.
  • Hence, we know most of the mass in the main
    asteroid belt less than 1/20 mass of Moon.
  • Measuring asteroid orbits (by astrometry) and
    rotation rates (by light curves) was relatively
    easy. Measuring actual sizes and masses was
    harder. Could use either occultation, or
    spectroscopy to get sizes.

Dr Conor Nixon Fall 06
26
ASTR 330 The Solar System
  • Lecture 9 Asteroid Orbits
  • Asteroids orbit the sun between 2.2 and 3.3 AU,
    with periods of 3.3 to 6 years. Collisions are
    rare (several per 10,000 years).
  • Gaps in the distribution of asteroid semi-major
    axes are known as resonance or Kirkwood gaps.
  • The gaps are caused by Jupiters gravity.
    Asteroids with a certain SMA have a fixed period
    by Kepler (3).
  • Orbits which cause the asteroid to repeatedly
    pass Jupiter in the same place are unstable.

Dr Conor Nixon Fall 06
Picture JPL/SSD Alan B. Chamberlain
27
ASTR 330 The Solar System
  • Lecture 9 Families and Classes
  • Asteroids which have similar spectroscopic
    properties and similar orbits are said to form a
    family.
  • We also note that some asteroids are bright with
    silicate features in the spectrum, while others
    are dark with water signature, hence 3 types
  • C-TYPE carbonaceous dark, with water
    primitive (e.g. Ceres)
  • S-TYPE stony, with silicates primitive (e.g.
    Eros)
  • M-TYPE (rare) metallic radar-bright (e.g.
    Psyche)
  • C-type (75) are outer edge of main belt, S-type
    (25) inner edge.
  • Densities are not useful indicators of
    composition, e.g. Psyche.

Dr Conor Nixon Fall 06
28
ASTR 330 The Solar System
  • Lecture 9 Asteroids contd.
  • Asteroids are also found
  • In the Lagrangian L4 and L5 points of Jupiters
    (and Mars) orbit, called Trojans.
  • In Earth crossing orbits NEAs/NEOs.
  • In elliptical orbits Centaurs.
  • Trojans and centaurs are redder than main-belt
    asteroids.
  • Visits
  • Gaspra (1991) by Galileo. Found irregular
    object, craters.
  • Ida (1993) by Galileo. Found moon (Dactyl), more
    cratered than Gaspra.
  • NEAR-Shoemaker at Mathilde found very dark,
    slow rotating object.
  • NEAR-Shoemaker at Eros orbited and landed.
    Found flat-bottomed craters filled with dust.

Dr Conor Nixon Fall 06
29
ASTR 330 The Solar System
  • Lecture 10 Comets
  • Comets are small primitive bodies from the outer
    solar system.
  • Whereas asteroids are mainly rock and metal,
    comets are mainly ice.
  • When comets approach the inner solar system
    their volatiles evaporate forming a temporary
    atmosphere (coma) and tail.
  • Plasma or ion tail is ionized volatile material.
  • Dust tail is dust particles released by
    vaporization of the volatiles.

Dr Conor Nixon Fall 06
Figure credit thursdaysclassroom.com
30
ASTR 330 The Solar System
  • Lecture 10 Comets - contributions
  • Tycho Brahe made important contributions to
    cometary science in the 16th century. By parallax
    he showed that the comet was further than the
    Moon, hence not in Earths atmosphere. Also
    showed that the comet head is as big as the
    Earth.
  • Halley was the first to find convincing proof of
    cometary re-occurrence. He successfully predicted
    the return of his namesake in 1758.
  • Comets follow elliptical orbits, and these are
    often inclined with respect to the planet orbits.
  • Long (200 yrs) and intermediate (30-200 yrs)
    period comets come from Oort cloud. Short period
    comets are from Kuiper belt.

Dr Conor Nixon Fall 06
Diagram Tim Stauffer
31
ASTR 330 The Solar System
  • Lecture 10 Composition etc
  • Largest component of comets is water ice. Also
    perhaps 10 CO, plus CH4, NH3, CO2 and others.
  • Molecules quickly ionized or dissociated (broken
    up) by solar radiation after leaving the nucleus,
    see H2O, CH, CH2, OH, NH etc.
  • Tail colors
  • Hydrogen envelope is blue due to H emission.
  • Plasma tail is blue due to CO fluorescence
    (straight tail).
  • Dust tail is yellow due to reflected sunlight
    (curved tail).

Dr Conor Nixon Fall 06
Picture Nanjing University Astr.
32
ASTR 330 The Solar System
  • Lecture 10 Comet missions and fates
  • Comet close-up missions
  • Giotto/Vega missions to Halley (1986). Found a
    dark (4 albedo) small nucleus (16x8x8 km).
  • Deep Space 1 passed Borelly in 2001 darker than
    Halley.
  • Stardust passed Wild-2 in Jan 2004.
  • Also note S-L 9 impact with Jupiter.
  • Possible fates of a comet
  • Total evaporation
  • Dead comet
  • Collision
  • Gravitational ejection

Dr Conor Nixon Fall 06
33
ASTR 330 The Solar System
  • Lecture 1-10 Quiz
  • What is meant by a geocentric universe? A
    heliocentric one?
  • Give a major contribution to astronomy by each of
    the following Aristotle, Ptolemy, Copernicus,
    Kepler, Galileo, Newton.
  • How old is the Sun, and what is the name of the
    mechanism which powers it?
  • Name the three visible layers of the Suns
    atmosphere, and give an approximate temperature
    for each.
  • What information can we tell about a planet from
    infrared spectral lines?
  • Give three examples of volatile species in the
    solar system, and say where they could be found.

Dr Conor Nixon Fall 06
34
ASTR 330 The Solar System
  • Lecture 1-10 Quiz
  • Why did the gas cloud collapse to a disk and not
    a point why did everything not fall into the
    Sun?
  • Why are the inner planets volatile-poor while
    the outer planets are volatile-rich?
  • Name three famous meteorites, and say what they
    are famous for.
  • Why are the Allan Hills in Antarctica a good
    place to hunt for meteorites?
  • What is the meaning of (a) parent nucleus (b)
    daughter nucleus (c) half-life?
  • Basaltic meteorites are another type of
    differentiated meteorite. What does the term
    mean? From what part of the parent body do
    basalts come?

Dr Conor Nixon Fall 06
35
ASTR 330 The Solar System
  • Lecture 1-10 Quiz
  • What are the three main asteroid types?
  • What are resonance gaps, and why do they occur?
  • Give the general properties of comet orbits are
    their orbits similar to those of the planets?
  • It has been stated that comets are actually very
    dark. How come we can see them?

Dr Conor Nixon Fall 06
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