Recap Our Solar System I

1
Recap Our Solar System (I)

• What sky observations are used to build a
  calendar ?
• How do you explain the changing shape of the Moon
  ?
• What is the reason for having seasons on Earth ?
• What are the main characteristics of Earth, which
  distinguish it from other planets in our solar
  system?
• Explain why Earth has so much atmospheric oxygen.
• Which is the hottest layer in Earths atmosphere
  ?
• How do you explain auroras ?

2
Recap Our Solar System (II)

• What are the main differences between Earth and
  Moon ?
• Explain two phenomena which relate to the
  Earth-Moon system.
• Name the 3 groups of planets in our solar system
• Name the most important characteristics of
  Mercury, Venus, Mars.

3
Giant Planets Jupiter

• Jupiter, with a radius about 11 times that of
  Earth, is about 2.5 times larger than all other
  planets put together.
• Its density, a quarter of Earth density, is
  similar to that of the Sun and so is its
  composition.
• Revolution of 11.86 years, and a full spin in
  about 10 hours.
• Layered structure (going towards its center)
• 1000km of hydrogen atmosphere (but also, ammonia
  ice and water ice)
• 20,000km of liquid molecular hydrogen (no solid
  surface)
• 40,000km of liquid ionized hydrogen
• 10,000km of rocky-metallic core. Temperature at
  the center about 20,000oC.
• Winds of 540km/h
• the Great Red Spot is a high-pressure system with
  color due to phosphorus.
• Huge magnetic fields extending to 4 -7 millions
  km produce auroras 100,000 brighter than on
  Earth.

4
Jupiter

• Jupiter Signature
• The largest planet in the solar system
• Hydrogen-based structure

5
Jupiters Moons

• Jupiter has 16 moons and a faint system of rings
  of particles of dust, which were blasted off the
  moons by meteor impact.
• 12 moons are small (R5-130km) while 4 are
  comparable with our Moon and were discovered by
  Galileo in 1610.
• In increasing distance from Jupiter Io, Europa,
  Ganymede and Callisto.
• Io and Europa have a density similar to our Moon
• Ganymede and Callisto have lower densities, due
  to a lot of ice.
• Callisto and Europa might have a liquid
  subsurface ocean with some elementary forms of
  life.
• Ganymede might have a metallic core
• Io has a lot of volcanic activity.

6
Jupiters Moons
Europa
Io
7
Giant Planets Saturn

• Saturn has a radius 9 times larger than Earth,
  revolution29.5 years, spin10 hours and 39
  minutes.
• It has about half of Jupiters density (the least
  dense among planets). Its structure has
• A core with R12,000km with rocks, metals
• 17,000km of liquid ionized hydrogen
• 30,000km of liquid molecular hydrogen
• Hydrogen atmosphere, magnetic field, high winds
  (up to 1500km/h), storms
• Saturn was investigated by Pioneer 11 in 1979,
  Voyager in 1980/81 and by Cassini in August 2004.

8
Saturn
Saturn Signature The rings expanding 1
light-sec. from the planet
9
Saturns Rings and Moons

• Saturns 3 rings expanding almost 1 light-second
  from surface (some faint rings extend to 1.5
  light-seconds) but with a vertical thickness of
  only 150m. They contain ice and ice-coated rock
  particles of up to tens of meters in size. As
  Saturn moves around the Sun the aspect of rings
  seen from Earth changes.
• Saturn also has at least 18 moons
• most are small, 4 are medium size and one (Titan)
  is larger than Mercury.
• Titan is quite unique as it has an atmosphere
  with 995 nitrogen and 5 methane. This
  atmosphere with a density twice higher than on
  Earth has hydrocarbons. But at 178oC liquid
  methane may exist only under a crust of solid
  methane.
• Cassini investigated this moon at the end of 2004.

10
Saturns Titan
11
Giant Planets Uranus

• Uranus is the first planet discovered with a
  telescope in 1781.
• Its radius is 4 times that of Earth,
  revolution84 years, spin17 hours.
• Its axis is tilt at 98o which makes one season 42
  years long when Voyager 2 flew past Uranus in
  1986 its South pole was facing the Sun North
  pole will face the Sun in 2030.
• Its atmosphere with 83 H, 15 He and 2 methane,
  which absorbs red light making the planet look
  green-blue.
• Its structure
• 25 core of rocks and metals
• 60 middle ocean of ionized ice
• 15 dense hydrogen layer.
• Surface temperature is -215oC and weak magnetic
  field.
• Uranus has at least 10 narrow dark rings and 15
  moons.

12
Uranus
Uranus Signature Its green-blue color due to
atmospheric methane
13
Giant Planets Neptune

• Neptune was discovered in 1846.
• Its radius is 4 times that of Earth,
  revolution164.8 years and spin16 hours.
• Density 20 higher than Earth.
• Atmosphere similar to Uranus 80 H, 19 He and
  methane 1-2. In 1989 it had a Great Dark Spot
  which disappeared.
• Like Jupiter and Saturn, Neptune radiates more
  energy than it receives from the Sun (hot
  interior). Like with Uranus, its magnetic field
  is generated in the ice-rich envelope.
• Neptune has 5 faint rings and 8 moons.
• Triton (R1350km) is the largest moon with 80
  reflectivity and with T-236oC was the coldest
  body investigated by a spacecraft (Voyager 2).
  Polar caps with nitrogen ice and geysers of
  hydrocarbon-rich material. Triton moves in a
  direction opposite to Neptunes spin and will
  probably break.

14
Neptune and Triton
Triton
Neptune

• Neptune Signature
• Similar to Uranus
• The system with Triton

15
Pluto

• Discovered in 1930, following speculations
  related to the study of Uranus.
• Smaller than our Moon (R1650km), revolution248
  years, spin6.387days, tilt17 degrees.
• Structure of rock and ice polar nitrogen and
  methane ice.
• Its large moon, Charon, rotates around Pluto and
  spins in 6.387 days, showing the same hemisphere
  to each other. Pluto is probably part of the
  Kuiper-belt of ice-rich objects that populate
  the outer regions of the solar system.

16
Pluto
Pluto Signature Until recently, the most remote
solar planet
17
Asteroids(I)

• Asteroids, or small planets, are small cosmic
  bodies with a radius below 500 km which revolve
  around our Sun.
• The first, Ceres, was discovered in 1801 and is
  the largest (R470km).
• Today we know over 4000 asteroids, most of them
  of irregular shapes.
• The main belt is between Mars and Jupiter.
• The Trojans are two groups on the same orbit as
  Jupiter (60 degrees before and after the planet).
  
• The Centaurs are a group between the orbits of
  Saturn and Neptune this group together with
  Pluto are part of the larger Kuiper belt that
  surrounds our planetary system.
• 3 groups (Atens, Amors and Appolos) are close to
  Earth and about 2000 asteroids (with a radius
  over 500m) closely approach the orbit of Earth.

18
Asteroids (II)

• Telescopes see asteroids as tiny points of light,
  but spectral analysis and radar showed that
  different groups have different properties.
• In the main belt some are outer C-type
  (carbon-rich compounds), inner S-type
  (silicaceous) and M-type (metallic).
• Kuiper belt has ice-rich asteroids.
• First close look by Galileo spacecraft in 1991
  (Gaspra seen from 1,600 km)
• Most astronomers believe that asteroids were
  debris left when planets were formed 4.5 billion
  years ago.

19
Comets

• Comets , with their bright fuzzy head and a long
  tail, are a dramatic spectacle.
• Edmund Hailey was the first to establish their
  origin. His comet made the most recent return in
  1986.
• Comets are of short-period (under 200 years
  orbital period) or long-period type.
• Composition
• Their nucleus is a fluffy lump of ice a few kms
  wide. Near the Sun it evaporates, but being rich
  in carbon it emits jets of dust and gas.
• UV radiation ionizes atoms and the solar wind
  accelerates these ions. When electrons are
  recaptured atoms reemit light as a type 1 tail.
• Sunlight also propels small particles of dust out
  of the head and these are the type 2 tail. The
  tail can be very long (twice than the distance
  Earth-Sun).

20
Meteoroids

• Meteoroids are small interplanetary particles of
  size between micrometer and meter.
• They go through thermosphere at high speeds and
  disintegrate producing traces of ions which
  produce short-lived trails of light, called
  meteors (shooting stars).
• A typical naked-eye meteoroid is visible around
  110km and burns by 75km altitude.
• Most of meteors have densities lower than water.
  They can be sporadic or shower. Some come from
  comets (ex. the Leonid shower).

21
Meteorites

• Meteorites are larger than meteoroids and after
  plunging through the atmosphere they reach the
  ground. They form a fireball, that can be
  brighter than Moon or even the Sun.
• Classes stony, stony-iron and iron
• Impact craters West Australia, Namibia,
  Arizona, equivalent to nuclear explosions.
• 1908 Tunguska small asteroid or comet nucleus.
• Most meteorites are 4.55 billion years old. Some
  originated from our Moon or Mars.