Welcome to the Solar System

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Chapter 7

• Welcome to the Solar System

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Our Solar System

• Human knowledge has only recently been able to
  determine the extent of our solar system. We now
  know that ours is one of several planets that
  orbit an ordinary star.
• Comparative Planetology says that we can learn
  more about our planet by studying it in the
  context of other planets.
• If you look at our solar system on a whole, the
  planets disappear when compared to the distances
  between them.

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Motions of the Planets

• From this diagram, we can see that the planets
  have nearly circular orbits, and lie nearly in
  the same plane,
• All planets orbit the Sun in the same direction,
  counterclockwise when looking down from above the
  Earths north pole,
• Most planets rotate in the same direction in
  which they orbit, as does the Sun,
• Most large moons behave similarly.

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Terrestrial and Jovian Planets

• Terrestrial planets are like the Earth. They are
  composed of rock and metals and have a solid
  surface. They usually have few moons, if any.
  They also lie closer to the Sun. m, v, e, M
• Jovian Planets (Gas Giants) are larger and
  composed of mostly hydrogen, helium compounds
  water, ammonia, methane and have no solid
  surface. They may have larger moons and usually
  have several. They also tend to have rings.
  Because of their size, we believe they tend to
  form farther from a star. J, S, U, N

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Asteroids Comets

• The leftovers and debris of the Solar System can
  be found as asteroids and comets.
• Asteroids mostly come from the Asteroid Belt,
  between Mars and Jupiter, or roam the Solar
  System. They orbit in the same direction as the
  planets. More than 10,000 have been discovered.
• Comets are small objects made of ice and rock.
  They are not common in the inner Solar System,
  and generally come from the Kuiper Belt
  (30-100AU) or the Oort Cloud (be upwards of a trillion comets associated with
  our Solar System.
• There are vast distance between the asteroids,
  and likewise between comets in their realm.

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A Quick Tourof the Solar System
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The Sun

• The Sun is a giant ball of dense gas and plasma.
  It is fueled by Hydrogen fusion at its core. It
  contains 99.9 of the mass of the Solar System.
• Radius 695,000 km
• Mass 333,000 me
• Surface is composed of a rolling sea of
  hydrogen/helium gas, 6000-10000 K.

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• Mercury
• First Planet from Sun
• 0.39 AU from Sun
• Radius 2,440 km
• Mass .055 me
• Mercury is a cratered and desolate world. The
  temperatures range from -150C (-240F) on the
  dark sideto 425C (800F) on the sidefacing the
  Sun.
• Mercury has an iron core and magnetic field
  like Earth.
• Revolves around Sun every 88 Earth Days
• Rotates every 176 Earth Days

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• Venus
• Second Planet from Sun
• 0.72 AU
• Radius 6,051 km
• Mass 0.815 me
• Venus similarities to Earth end at its size and
  basic composition. Venus is the hottest planet in
  the Solar System (up to 450C/850F), all day,
  every day! The atmosphere is filled with
  greenhouse gasses and rains sulfuric acid. No
  active volcanoes have been seen.
• Revolves around Sun every 224.7 Earth Days
• Rotates every 116.8 Earth Days

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• Earth
• Third Planet from Sun
• 1.0 AU from Sun
• Radius 6,378 km
• Mass 1 me
• The Earth is a true oasis in space. The
  atmosphere is primarily composed of oxygen and
  nitrogen and the temperatures are consistent and
  moderate. The vast water oceans comprise 80 of
  the surface area of the planet.
• Revolves around Sun every 365 days
• Rotates every 24 hours

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• Moon
• While the Moon is not a planet, because it
  revolves around the Earth, it has a very special
  place in our history. It is likely that the Moon
  has prevented impacts and help to form a dynamic
  system that was favorable for formative life on
  Earth.
• The Moon happens to be moving slowly away from
  the Earth, and presently subtends almost exactly
  the same angle as the Sun, allowing for total
  eclipses.
• Most terrestrial planets do not have moons, and
  none have a moon as large. The origins of the
  Moon is an important topic of scientific debate.

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• Mars
• Fourth Planet from Sun
• 1.52 AU from Sun
• Radius 3,397 km
• Mass .107 me
• Mars is a cold dead world. It has a thin carbon
  dioxide atmosphere. Dust storms can encompass the
  globe. It has two small moons. There are signs of
  violent upheaval, cratering and volcanic activity
  in the distant past.
• Mars revolves around the Sun every 687 Earth
  Days
• A Martian day is 24h 39m (earth time)

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• Jupiter
• Fifth Planet from Sun
• 5.20 AU from Sun
• Radius 71,492 km
• Mass 317.9 me
• Jupiter is a great gas giant, with many moons
  and a great gravitational influence on the Solar
  System. Vast storms rage on Jupiter for hundreds
  of years. The moons of Jupiter may even harbor
  life.
• Jupiter revolves around the Sun once every 11.9
  Earth Years
• Jupiter rotates once every 9.93 earth hours

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• Saturn
• Sixth Planet from Sun
• 9.54 AU from Sun
• Radius 60,268 km
• Mass 95.18 me
• Saturn is the second largest planet in the Solar
  System. It is a huge gas giant with a remarkable
  ring system. Saturn has at least 30 moons,
  including Titan which is larger than Mercury. The
  Cassini probe is exploring the Saturn system
  starting in 2004.
• Saturn revolves around the Sun once every 29.4
  Earth years
• Saturn rotates every 10.6 Earth hours

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• Uranus
• Seventh Planet from Sun
• 19.19 AU from Sun
• Radius 25,559 km
• Mass 14.54 me
• Uranus is much larger than Earth and composed of
  largely hydrogen, helium and methane (thus the
  blue-green color). Like the other gas giants, it
  does not have a solid surface. Uranus has at
  least 21 moons.
• Uranus revolves around the Sun on its side,
  every 83.8 Earth years
• Uranus rotates every 17.2 Earth hours

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• Neptune
• Eighth Planet from Sun
• 30.06 AU from Sun
• Radius 24,764 km
• Mass 17.13 me
• Neptune is roughly the same size as Uranus.
  Neptune has at least 8 moons, Triton being larger
  than Pluto. Triton is the only moon in the Solar
  System known to orbit its planet backwards
  opposing its rotation.
• Neptune revolves around the Sun once every 164
  Earth years.
• Neptune rotates once every 16.1 Earth hours

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• Pluto ( Charon)
• Ninth Planet from Sun
• 39.54 AU from Sun
• Radius 1,160 km
• Mass .0022 me
• Pluto and Charon orbit each other in the outer
  realms of our Solar System. Pluto is barely
  considered a planet, composed mostly of ices.
• Pluto takes 248 Earth Years to revolve around
  the Sun
• Pluto rotates every 6.39 Earth days

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Exploring the Solar System

• Spacecraft are sent on missions to observe and
  explore the Solar System and beyond.
• Types of missions include
• Flybys
• Orbiters
• Landers (probes)
• Sample Return Missions

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Careful planning allowed Voyager II to visit
several planets as flybys and gather more
scientific data.
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Missions to Mars have included landers in recent
years, in an attempt to learn more about the
surface and possible signs of water/ice and life
in the present or distant past.
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Future Space Missions

• For a list of current and planned missions at
  NASA, http//spacescience.nasa.gov/missions/studie
  s.htm