Basic facts

1
Basic facts

• The Solar System is composed of
• 1 Star the Sun
• 9 Planets Mercury, Venus, Earth, Mars,
  Jupiter, Saturn, Uranus, Neptune Pluto
• Dwarf Planets
• Over 100 Moons (and counting)
• Asteroids, Comets, Meteoroids, and other objects!
• The planets all orbit around the Sun in the same
  direction (and most moons orbit around their
  planet the same way).
• Relative to Earths orbital plane, most other
  planets orbit in roughly the same plane. (Most
  inclined Mercury at 7º)
• Most planets have near circular orbits. (Most
  eccentric Mercury at e 0.21)

2
Terrestrial vs. Jovian Planets
3
Stellar Debris

• Asteroids fragments of rocky objects
• Range in size up to 100 km in diameter.
• Irregularly shaped, and cratered.
• Similar in composition to outer layers of
  terrestrial planets.
• Comets small icy bodies (dirty snowballs).
• Large elliptical orbits can bring comets in close
  to the Sun.
• Recent studies suggest they are at least 50 rock
  and dust.
• Meteoroids specks of dust and rock similar in
  composition to Asteroids, but much smaller (less
  than 100 m in diameter).
• We study small objects like these because they
  have been untouched by evolution over time (good
  indication of solar system composition at the
  time of formation.)

4

• Most asteroids like within the asteroid belt,
  between Mars and Jupiter.
• Trojan asteroids share Jupiters orbit. These
  asteroids are trapped by specific gravitational
  pulls from Jupiter and the Sun.
• Some asteroids have been pushed into elliptical
  orbits by Jupiter, causing this to move closer in
  to the Solar System.
• Observations of asteroids suggest that they are
  not completely solid, but rather a collection of
  fragments which never completely reformed.

5
Comets

• Comets have highly elliptical orbits, bringing
  them close to the Sun, but also very far away.
• Change in distance causes change in heating.
• As a comet approaches the Sun, its ices sublimate
  (change directly from solid to gas).
• Comets form two tails
• Gas (ion) tail (type I)
• Ionized gas carried away by the solar wind.
• Generally points away from the Sun.
• Dust tail (type II)
• Dust loosened by vaporizing ice, pushed away be
  solar wind.
• Follows orbital path of comet.
• Coma halo of gas and dust surrounding the
  nucleus.
• Nucleus 10 100 km
• Coma 105 km

6
Comet Nuclei

• Comet nuclei
• Porous rock, irregular in shape.
• Ices (H2O, CO2, ammonia, etc.)
• Density 0.1 0.25 g/cm3
• As comet nears the sun, its surface fragments and
  releases jets of material.
• Probably faults or vents in surface of nucleus.

7
The Origin of Comets

• Long period comets (P gt 200 yrs.)
• Randomly inclined orbits.
• Random direction and revolution.

• Short period comets (P lt 200 yrs.)
• Orbits lie within 30 of the plane of the Solar
  System.
• Most revolve counterclockwise.

• Oort Cloud
• Spherical cloud of icy bodies.
• 104 to 105 AU in radius.

• Kuiper Belt
• Disk of icy planetesimals.
• 30 to 100 AU from the Sun.

8
Meteoroids

• Meteoroid Speck of dust and rock which
  encounter Earths atmosphere and either burn up
  or fall to the ground. (Most only about 1g in
  mass).
• Meteor Flash across the sky as the meteoroid
  burns up.
• Meteorite Remnant of a meteoroid that reaches
  the ground.

Above atmosphere
In atmosphere
Hits ground
9
Meteor Showers

• As comets orbit the Sun, they lose material and
  leave a trail.
• As the Earth passes through that trail, the
  particles fall towards Earth in the form of
  meteor showers.
• Meteor showers are designated by the
  constellation from which they appear to be
  originating.

10
Radioactive Dating

• Radioactive Decay process through which massive
  particles naturally decay into less massive ones.
• Radioactive Dating determining the age of an
  object based on how certain particles have
  radioactively decayed over time.
• The Earth oldest samples suggest an age older
  than 4.3 to 4.4 billion years.
• The Moon lunar rocks suggest an age older than
  4.48 billion years.
• Mars meteorite samples discovered in the
  Antarctic suggest an age older than 4.5 billion
  years.
• Meteorites suggest an age older than 4.6
  billion years.
• Our solar system is thought to be around 4.6
  billion years old.

11
Comet Impacts

• Will a comet (or asteroid) hit the Earth?
• 1994 Comet Shoemaker-Levy hit Jupiter.
• Evidence of other impacts on the Moon and other
  solar system bodies.

12
Evidence of Impacts on Earth

• Barringer Meteor Crater 25,000 years old and
  1.2 km wide.
• The Tunguska Event (30 June 1908) an impact in
  Siberia thought to be due to an meteorite
  exploding meters off of the ground.

13
The Extinction of the Dinosaurs

• Layer of iridium found in sediment all around the
  world.
• 65 million years ago.
• Iridium common in meteorites, but not on Earths
  surface.

• Impact thought to have led to the extinction of
  the dinosaurs.
• As impact occurs, shocks and tsunamis would kill
  nearby life.
• Rock heated by impact, thrown into the air,
  causing forest fires around the world.
• Dust in atmosphere blocks sunlight for at least a
  year.
• CO2 released into atmosphere.

14

• Likelihood of impacts based on how much energy
  they would release.