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Asteroids, Comets and Dust

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Title: Asteroids, Comets and Dust


1
Asteroids, Comets and Dust
2
Remnants of Our Solar Systems Formation
  • Asteroids
  • Meteorites
  • Comets
  • Dust
  • Gas

3
Planetesimals
  • Material left over from the Suns formation and
    the construction of the planets are the building
    blocks of the planets called planetesimals which
    include
  • Asteroids primarily fused rock and metal with
    some ices in the outer asteroid belt
  • Comets primarily ices and dust grains with
    minor amounts rock and metal
  • As well as materials in the form of
  • Dust
  • Gas
  • Note the asteroid and comet planetesimals are
    now called Small Solar System Bodies (SSBS)

4
Asteroids
5
Asteroids
  • Asteroids were formed in the inner solar system
    during the early solar system formation period
    following the Suns intense T-Tauri emission
  • Collisional heating fused larger and larger
    fragments together by accretion
  • Larger fragments pulled surrounding materials to
    build larger planetesimal asteroids
  • Heating from impacts fused smaller asteroids, and
    created molten cores in larger asteroids

6
Asteroids
  • Fused and partially fused rock fragments became
    carbonaceous asteroids
  • High-density molten fragments became metallic
    asteroids
  • Primarily iron with some nickel

7
Asteroids
  • Asteroids types
  • S-Type (Silicaceous)
  • About 17 of asteroids
  • Relatively bright and reflective
  • Composition is metallic iron mixed with iron- and
    magnesium-silicates
  • S-type asteroids dominate the inner asteroid belt
  • M-type (Metallic)
  • Relatively bright and reflective
  • Composed mainly of metallic iron
  • M-type asteroids inhabit the belt's middle region

8
Asteroids
  • Asteroids types
  • C-type (Carbonaceous)
  • More than 75 of known asteroids
  • Very dark and non-reflective
  • Solid composition similar to solar system makeup,
    except depleted in hydrogen, helium, and other
    volatiles
  • C-type asteroids are found mainly in the belt's
    outer regions
  • D-type
  • Very dark and non-reflective
  • Reddish in color

9
Asteroids
  • Distribution throughout solar system is dominated
    by gravitational forces from the largest planets
  • Jupiter has collected and distributed most
    asteroids in regions of orbital stability or gaps
    relating to instability
  • Earlier known as minor planets
  • Largest asteroid named Ceres is a dwarf planet

10
Asteroids
  • Orbit resonances and Jupiters stability points
    create distinct patterns and gaps in asteroid
    distribution
  • Mars generates small but significant stability
    boundaries in asteroid distribution near the
    planet
  • Note Asteroids are also classified by their
    orbits, and by their reflected spectra

11
Asteroid Distributions
12
Asteroid Distributions
13
Asteroid Distributions
14
Asteroids
  • Average shapes and sizes
  • Asteroids, which are the remnants of the early
    solar system formation, reflect the conditions in
    the early inner solar system
  • Size of these solid bodies varies between pebbles
    to irregular-shaped bodies several hundred km in
    diameter
  • Ceres, the largest asteroid that has a mean
    diameter of 950 m
  • Since asteroids are generally small, their
    gravitational pressure is not enough to force
    them into a spherical in shape

15
Asteroids
  • The asteroid explorer named Dawn, launched
    September 27, 2007 explored Vesta, the second
    largest asteroid, from July 2011 to September,
    2012
  • Dawn was then sent to Ceres for a multi-year
    investigation of the dwarf planet beginning in
    February, 2015
  • Dawn spacecraft is powered by three xenon ion
    engines

16
Asteroid Examples
With the exception of Ceres, the asteroids are
irregular in shape And although the shapes vary,
all are irregular and cratered
17
Asteroid - Impacts
  • Impacts and cratering on Earth from comets and
    asteroids is roughly proportional to the object's
    mass since hyperbolic velocity is typically 20-40
    km/s
  • Evidence of the type of impact object can be made
    by analysis of the crater rim or ejecta
  • High levels of iridium are found in asteroid
    samples and debris
  • Diameter Energy of impact Crater diameter
  • (Megatons of TNT) (km)
  • 20 m 5 0.2
  • 100m 100 1.0
  • 1 km 10,000 10
  • 10 km 10,000,000 100

18
Asteroid - Impacts
  • Impact Examples
  • Tunguska Siberia (1908)
  • Comet/carbonaceous asteroid is estimated at 50 m
    diameter
  • No crater was generated, which means that it had
    to be a weak (carbonaceous) meteorite or a comet
  • 15 M ton energy equivalent
  • Air burst explosion devastated 1,000 sq km of the
    surface

19
Asteroid - Impacts
  • Impact Examples
  • Arizona Crater (50,000 years ago)
  • 50 m iron/nickel meteorite
  • 1.3 km crater
  • 200 Megaton energy equivalent

20
Asteroid - Impacts
  • Impact Examples
  • Chicxulub, Yucatan impact (65 M years ago)
  • 13 km diameter asteroid
  • 130 km crater diameter
  • 100,000,000 Mton energy equivalent
  • 70 species exterminated on Earth

21
Meteorites
22
Meteorites
  • Meteorites are asteroid materials that survive
    atmospheric entry and can be found on the Earths
    surface
  • Meteor visible event of cosmic debris entering
    Earths atmosphere
  • Meteorite Cosmic material entering Earths
    atmosphere and surviving to reach Earths surface
  • Meteoroid cosmic debris in space (asteroid or
    cometary material)

23
Meteorites
  • Meteorites are classified primarily by their
    composition similar to asteroids (silicate rock,
    metal, and chondrites)
  • Chondrites (85 collected)
  • Named after chondrules (spheres of silicate and
    dust materials) found within the solid rock
    bodies
  • Achondrites (8 collected)
  • Silicate rock, but no chondrules found within the
    solid body
  • Iron (5 collected)
  • Iron and nickel metal pieces from the interior of
    larger asteroids that formed metal cores

24
Meteorites
  • Stony-iron (1 collected)
  • A mixture of iron-nickel metal and silicate rock
    that may have originated between the mantle and
    core regions of larger asteroids

25
Meteorites
  • Average composition
  • Although the meteorites vary widely in their
    composition, the average is roughly the same
    composition as the inner solar system
  • Chemical and physical changes are introduced by
    atmospheric heating and surface impacts

26
Asteroids
  • Average composition
  • The average composition of meteorite samples
    represents inner-belt asteroid composition
  • Oxygen       36.3
  • Iron             25.6
  • Silicon         18.0
  • Magnesium 14.2
  • Aluminum   1.3
  • Nickel          1.4
  • Calcium       1.3
  • Sodium        0.6

27
Comets
28
Comets
  • Comets and cometary debris is composed primarily
    of ices and dust (Si, C, Al, Fe, etc.)
  • Gases are given off (evolved) by the comet
  • Sublimation
  • Generally a small loss because of the extremely
    low temperatures in space
  • 20-50 K
  • Solar heating
  • Strong inside Earths orbit (1 AU)
  • Rapidly age comets because of their porous
    structure

29
Comets
  • Often described as dirty snowballs
  • White-blue-green ice compounds are mixed with
    brown-black-grey dust
  • Dust grains include carbon compounds, silicate
    compounds, and iron compounds, including graphite
    which is black
  • Most abundant ices are carbon dioxide, ammonia,
    methane, and water

30
Comets
  • Extend even beyond the heliosphere in a region
    called the Oort cloud
  • Another extended region of the planetary disk
    contains more comets and dwarf ice planets called
    the Kuiper Belt

31
Comets
  • Distant solar system diagram in the horizontal
    plane
  • Shown are the positions of objects with
    semi-major axes greater than 5 AU (orbital
    periods greater than 11 years) on 2008 January 1
  • The orbits and positions of Earth, Jupiter,
    Saturn, Uranus, Neptune, Pluto, and comets Halley
    and Hale-Bopp are also shown
  • Asteroids are yellow dots and comets are
    symbolized by sunward-pointing wedges
  • The vernal equinox is to the right along the
    horizontal axis (X direction)

32
Comets
  • Top view of the distant solar system
  • Shown are the positions of objects with
    semi-major axes greater than 5 AU (orbital
    periods greater than 11 years) on 2008 January 1
  • The orbits and positions are shown for the
    trans-Neptunian objects Eris, Quaor, Sedna,
    Orcus, Hale-Bopp and others
  • The vernal equinox is to the right along the
    horizontal axis (X direction)

33
Comets
  • Typical composition
  • Spectral emission of the Deep Impact collision
    with comet Tempel 1 showing the distinct
    signature of water (as ice)
  • Also present are several hydrocarbons, and carbon
    dioxide

34
Trans-Neptunian Objects
35
Trans-Neptunian Objects
  • Recent discoveries of the icy bodies populating
    the outer solar system by the powerful Hubble
    Space Telescope and several new ground-based
    adaptive-optics telescopes have revealed hundreds
    of Pluto-like bodies roughly in the same plane as
    the major planets
  • This region that extends beyond Neptune, called
    the Kuiper Belt after astronomer Gerard Kuiper,
    is populated with moon-like comets that resemble
    Pluto, but are generally much smaller

36
Trans-Neptunian Objects
  • The disk population is confined to a semimajor
    axis of about 55 AU, and clustered at specific
    positions with respect to integer fractions of
    Neptune's orbit period
  • Not only does Neptune's gravitation direct the
    motion of these outer bodies, Neptune has
    stabilized many of these icy bodies inside or
    outside the orbital resonance positions
  • Because of Neptune's fundamental role in
    shepherding these icy satellites, including
    Pluto, they are classified as Trans-Neptunian
    Objects (TNOs)

37
Trans Neptunain Objects
38
Dust
39
Dust
  • Small particles of material left over from the
    solar system formation, and from later collisions
    between planetesimals, are found throughout the
    planetary disk, but are less abundant closer to
    the Sun
  • Continual outward pressure from solar radiation
    has pushed most of the small particles outward

40
Dust
  • Although particle and dust concentrations occur
    around the planets, collections of the dust and
    debris can also be found at the Lagrange
    stability points L4 and L5
  • The nearest example is the Earth-Moon system that
    has both L4 and L5 regions populated by
    particles, but low in abundance
  • Trojan asteroids, asteroids found in Jupiter's 
    L4-L5 stability points in the Sun-Jupiter system,
    are much larger than the dust in the Earth-Moon
    system because of Jupiter's much larger mass
  • Dust accumulations can also be seen in a diffuse
    belt in the planetary plane known as the zodiacal
    belt

41
Asteroid Distributions
42
Jupiters Lagrange Stable Points
43
Dust
  • The most problematic material encountered by
    spacecraft are the most abundant particles (much
    larger than atoms and molecules)
  • This is the dust and small debris common in
    Earth-orbit
  • The damage is not catastrophic, but instead
    accumulates its erosive effects with time

44
Dust
  • Shielding from this small debris consists of the
    following
  • Sensitive instrument or optics use mechanical
    shades or coverings
  • Durable coatings are used for spacecraft surface
    integrity
  • Thin bumper shielding is commonly used for
    pressurized spacecraft and spacecraft on comet
    flyby missions where particles the size of sand
    can be a serious problem
  • A 10 mg sand grain traveling at 40 km/s has the
    destructive energy of a small-caliber bullet

45
Dust
  • Debris tracked in Low-Earth Orbit (LEO)

46
Dust
  • Orbital debris larger view showing outline of
    geostationary orbit

47
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