Chapter 23: Planets and their Moons

1

• Chapter 23 Planets and their Moons
• Artists concept of Saturn sized planet orbiting a
  distant star (detected by astronomers).

Fig. 23-CO, p.548
2
The Solar System

• Formed about 4.6 billion years ago from diffuse
  cloud of dust and gas (exploding stars) rotating
  in space (under gravity).
• Cloud composed of about 92 hydrogen, 7.8 helium
  (all other elements only 0.2 of Solar System).
• Sun formed under gravity, hydrogen fused some
  converted to helium fusion is source of Suns
  energy.
• Remaining matter formed disc-shaped rotating
  nebula that coalesced into planets. Early
  atmospheres (H and He) boiled off (escape
  velocity) or blown away by solar winds.
• Rock and metal left, terrestrial planets formed
  (solid rock with metallic cores).
• Planets in outer reaches of Solar System remained
  cool they are larger and called Jovian planets.
  Retained H and He.

3
The planets

• Terrestrial planets Jovian planets
• Mercury Jupiter
• Venus Saturn
• Earth Uranus
• Mars Neptune
• and.Pluto
• (dwarf planet)

4
Table 23-1, p.552
5
Mercury a planet the size of the Moon

• Radius is 2,400 km.
• Closest to Sun.
• Orbits Sun in 88 Earth days rotates 3 days in 2
  years (176 days Mercury time)
• Temp ranges from 427 degrees C (melt lead) to
  -175 degrees C (freeze methane).
• No atmosphere meteorite impact craters interior
  has cooled.
• Ice at poles no tilt in axis magnetic field
  (why?).

Fig. 23-1, p.553
6
Questions

• Describe implications of Mercurys lack of both
  an atmosphere and hot interior.
• Describe implications of greenhouse gases and a
  cool interior on Venus.
• Describe implications of the Moons size relative
  to Earth how does this account for geologic
  features found on Earth and on our Moon?
• Describe implications of Mars distance from the
  Sun (relative to Earth).

7
Venus the Greenhouse Planet

• Closely resembles Earth in size,
• density and distance from Sun
• Atmosphere is 90 times denser
• than Earth (1000 meters beneath
• the sea) 97 C02
• Why is the surface hotter than
• Mercury?
• Few craters landforms appear 300-500 million
  years old (catastrophic event?)
• today volcanic activity may have ceased 60 of
  surface is flat, with mountain
• chains and canyons Maat Mons (larger than
  Everest)
• Blob Tectonics? Surface too hot and plastic/or
  lithosphere too thick?

Fig. 23-2, p.553
8

• The volcano Maat Mons on Venus, Lava flows in
  foreground.
• Image from Magellan Spacecraft.

Fig. 23-3, p.554
9
Map of VenusLowland in blue highlands in yellow
and red-brown.
Fig. 23-4, p.554
10
The Moon

• 1600s Galileo named the
• plains maria (for seas)
• because he thought they
• were oceans.
• Heavily cratered.

Fig. 23-5, p.555
11

• Shows cratered
• surface of the
• moon.
• In some places
• there are craters
• within craters.

Fig. 23-6, p.555
12

• Six Apollo missions answered many scientific
  questions about the origin, structure and history
  of the Moon.

Fig. 23-7, p.556
13

• How did the Moon form?
• Most current hypothesis is that a large object,
  possibly larger than Mars, collided with Earth
  shortly after our planet formed. This vaporized
  silica-rich rocks, creating a cloud around the
  Earth that coalesced to form the Moon

Fig. 23-8, p.557
14

• This slide shows how the impact could have
  created vaporized rock that orbited the Earth and
  coalesced into the Moon about 4.5 billion years
  ago, similar to the solar nebula that created the
  planets.

Fig. 23-8a, p.557
15

• After the Moon formed, it was bombarded by
  meteorites that cratered the surface. This along
  with gravitational coalescence probably accounts
  for early melting of the Moon, which formed
  igneous rocks (e.g., basalt) found at the
  surface. Eventually the surface cooled some of
  the oldest rocks (of the highlands) are 4.4
  billion years old.

Fig. 23-8b, p.557
16

• Between 4.2 and 3.9 billion years ago swarms of
  meteorites bombarded the Moon again, and this,
  along with radioactive decay heating the interior
  of the Moon, resulted in magma erupting onto the
  surface and filling meteorite craters (and
  forming the maria that we see today).
• The Moon is much smaller than the Earth, so it
  cooled and has remained geologically inactive for
  the past 3.1 billion years.
• It might have a hot, molten core and water at the
  poles!

Fig. 23-8c, p.557
17
Mars A search for Lost Water

• Mix of old cratered terrain and younger,
  mountainous regions shown on the surface of Mars.
  Lava flows cover the plains.

Fig. 23-9, p.558
18

• Olympus Mons 25 km high and 500 km across,
  located on the Tharsis bulge which is the biggest
  volcanic plain it is the largest volcano on Mars
  and in our Solar System (nearly 3 times higher
  than Mount Everest).
• Blob tectonics (similar to Venus) could account
  for its massive sizehow?

Fig. 23-10, p.558
19

• More evidence for blob tectonics are tremendous
  parallel cracks split in the crust adjacent to
  the Tharsis bulge. There is no folding or
  offsetting of the cracks. Therefore, scientists
  suggest that a rising mantle plume formed the
  Tharsis bulge and its volcanoes (the cracks are
  from stretching during uplift of the crust).

Fig. 23-11, p.559
20
Martian Atmosphere

• Today the atmosphere is frigid and dry. Surface
  temperatures average -60 degrees C (-76 degrees
  F) at the equator (ice doesnt melt), and -120
  degrees C at the poles (frozen CO2). The
  atmosphere is very thin compared to Earth.
• Evidence shows the climate on Mars was once much
  warmer and water flowed across the surface.

21

• Recent research found layered sedimentary rocks,
  iron-rich minerals, salts and ripple marks. Mars
  contains water as ice at poles, and in
  subsurface soils

22
Valles Marineris

• A giant canyon was eroded by flowing water and is
  10 times larger and 6 times wider than the Grand
  Canyon. Also find eroded crater walls, alluvial
  fans and extinct stream and lake beds.

Fig. 23-12, p.560
23
Jupiter A star that failed

• The largest planet in our Solar System (71,000 km
  or 45,000 miles radius).

• Mostly Hydrogen and helium
• Sea of liquid molecular H2 He 12,000km deep
• At the bottom, 30,000oC under 100 trillion times
  Earth normal pressure
• H2 dissociates into 2H and atoms compress
• Electrons become free to flow like metals on
  Earth
• Liquid metallic hydrogen
• Generates Jupiters massive magnetic field

Fig. 23-14, p.563
24

• Jupiter (cont)
• Rocky core 10-20x Earth size
• Atmosphere is verified H2, He, with NH4, H2O, CH4
• Great Red Spot Earth would fit into it!
• Spot and bands have existed for centuries
• Galileos probe stopped transmitting at 130km in
  at 150oC (300oF) with 650km/hr winds at 22 bars
• Winds likely driven by heat from below

25
Moons of Jupiter

• By 2003, 60 moons were known. Most are small.
  The four discovered by Galileo are largest and
  most widely studied.
• Io innermost moon, about size of Earths Moon.
  Active volcanically. Gas and rock erupt to a
  height of 200 km. Galileo probe showed 100
  volcanoes erupting simultaneously. Gravitational
  pull of Jupiter and other moons causes great rock
  distortion and frictional heating. The surface
  is smooth (no craters) from lava (see slide).
• Europa similar to Earth. Interior composed of
  rock, much of surface covered by water, but water
  is frozen into ice crust. Galileo probe showed
  fractured, jumbled, chaotic terrain like Arctic
  ice on Earth (see slides).
• Ganymede and Callisto see next slides on
  Ganymede Callisto may have a subterranean ocean
  its surface is heavily cratered (what does this
  imply?).

26

• Io (left) Europa (right) Voyager spacecraft
  image. Great Red Spot shown along with turbulent
  cloud system.

Fig. 23-15, p.563
27

• Volcanic explosion on Io (Voyager I image).
  Eruption on horizon is ejecting material to an
  altitude of about 200 km.

Fig. 23-16, p.564
28

• The jumbled terrain of Europa resembles Arctic
  ice break up during spring. Scientists estimate
  the ice is a few km thick, and is floating on
  subsurface water.

Fig. 23-17, p.564
29

• Smooth, circular region (center left) formed
  when subsurface water rose to the surface of
  froze, covering older wrinkles and cracks in the
  crust of Europa. Water may be warmed by tidal
  effects. Could there be life at the subterranean
  oceans?

Fig. 23-18, p.564
30

• Ganymede has a magnetic field, possibly from a
  convecting metallic core surrounded by a silicate
  mantle and covered by water/ice. The surface is
  so cold it is brittle and acts like rock.

Fig. 23-19, p.565
31

• The surface of Ganymede is pockmarked by dense
  concentrations of impact craters (white spots)
  younger regions of fewer impact craters.

Fig. 23-20, p.565
32

• A close up of young terrain on Ganymede shows
  numerous grooves (gt 1 km wide). These grooves
  may have formed by recent tectonic activity?

Fig. 23-21, p.565
33

• Saturn
• The Ringed Giant
• 2nd largest planet.
• Lowest density of all
• planets (it would float
• on water).
• Composed primarily
• of H and He, with a
• small core of rock/metal
• and atmosphere similar
• to Jupiter (dense clouds
• great storms).
• Titan is largest of 31 moons that are known to
  orbit Saturn today. It is larger
• than Mercury, has an atmosphere (only moon known
  to have one probably
• because of its size and cold temperature)
  composed of nitrogen, methane and
• other gases. Temps avg. -180 degrees C,
  atmospheric pressure is 1.5 times
• greater than Earths surface. At these
  conditions, methane on Titan could act

34
Titan

• The Cassini-Huygens spacecraft was launched
  during 1997 to study Saturn and its moons. The
  Huygens probe (sent to study Saturns largest
  moon Titan) separated from the spacecraft (which
  arrived at Saturn during July, 2004) and landed
  on Titans surface during January of 2005. Why
  study Titan? One reason is that methane and
  nitrogen likely react to form simple organic
  compounds.

35
Assignment (dont do unless specifically assigned)

• You are presenting a paper at a scientific
  seminar on Titan (Saturns largest moon). Some
  scientists believe Titan more closely resembles
  the early Earth than Earth itself does today.
• Your presentation must cover the latest findings
  from scientific research on Titan, and then
  address the statement above from scientific
  data, discoveries, observations, etc., regarding
  Titan do you believe the above statement is
  accurate? Why or why not? Do you believe life
  (as we know it) could evolve on Titan? Why or
  why not?
• Your report must be a minimum of one page
  typewritten (single-spaced).
• http//www.esa.int/SPECIALS/Cassini-Huygens/index.
  html (could start here).

36

• Rings of Saturn
• Seven major rings with smaller ringlets
• Thickness from 10-25 meters, but extremely wide
  (425,000 km from inner to outer edge).
• Composed of dust, rock and ice larger particles
  at inner rings, clay size at outer rings.
• May be fragments of a moon that never coalesced,
  or remnants of a moon that formed and was ripped
  apart by Saturns gravitational field.

Fig. 23-23, p.566
37

• Voyager I and II planetary spacecraft provided
  valuable data on Jupiter, Saturn, Uranus and
  Neptune.

Fig. 23-24, p.567
38
Uranus and Neptune

• So distant, not known until the 1980s.
• Voyager II to Neptune after 12 years
• and 7.1 billion miles. Both planets thick
• atmospheres of H and He molecular H
• below this and interiors are methane,
• ammonia and water, with rock/metal cores.
• Both have magnetic fields tilted at 50-60 degrees
  from spin axis! Great storms rage on these
  planets (1,100 km/hr rip through Neptunes
  atmosphere, clouds rise and fall the Great Dark
  Spot is found on Neptune).
• Methane may decompose to C and H (from great
  pressure), and C may crystallize into diamond
  (releasing great energy).
• Uranus has rings and 22 moons Neptune has rings
  and 11 moons. Triton (largest moon) is about 75
  rock and 25 ice with craters, mountains and
  plains (filled with ice or frozen methane).

Fig. 23-25, p.568
39

• Data shows Pluto is the smallest planet
  (reclassified as dwarf planet during 2006) in
  the Solar System (smaller than Earths Moon).
  Its diameter and mass suggest it is made of rock
  and ice. Temp is about -220 degrees C, and
  surface may be frozen methane. Atmosphere is
  thin, composed of CO, N2 and CH4. Pluto and
  Charon (Plutos Moon) may be escaped moons from
  Neptune or Kuiper-belt objects?

Fig. 23-26ab, p.568
40

• Never visited by spacecraft, so how do we know
  Plutos properties?
• During 1978 Charon was discovered by measuring
  Charons orbit, can calculate relative masses of
  each.
• From diameter and mass calculations, Plutos
  density is less that granite and greater than ice
  (so mixture of rock and ice).
• During 2005, astronomers detected two other moons
  orbiting Pluto. Also, Xena discovered (10th
  planet!)it is 1.5 times larger than Pluto Many
  astronomers feel Pluto should be a Kuiper-belt
  object.

Fig. 23-26c, p.568
41
Asteroids, Comets and Meteoroids
23.8 Asteroids, comets, meteoroids

• Asteroids main belt between Mars and Jupiter
• Ceres the largest at 930km
• Asteroids change orbit frequently
• Some orbit close to, or cross paths with, Earth
  (may be reason for mass extinctions during
  history of Earth)
• 1 chance Earth will be struck with a 10km
  asteroid in the next 1,000 years

42
Cometsbelow, ejecta plume from Deep Impact
Probe colliding with comet Tempel 1 during 2005.
Analysis of impact ejecta suggest comet surface
is fine dust organic compounds detected in near
surface interior (basis for living organisms?)
43

• Comets from the Greek for long-haired
• long elliptical orbits
• Spend most of their time past Pluto
• Mostly a ball of water-ice and methane
• No tail until it gets close enough to the sun
• Nucleus the dense ball of the comet proper
• Coma the bright surrounding ions
• Tail the ions streaming away in the solar wind
• (can be millions of km long). Halleys comet
  had a coma radius of 4500 km when it passed
  Earth during 1986.
• Some contain organic compounds

44

• Comet Hale-Bopp was the brightest comet see from
  Earth in decades. It was brightest in March and
  April of 1997.

Fig. 23-27, p.569
45
Fig. 23-28, p.570
46
Meteoroids

• Fragment of comet or asteroid that orbits the
  inner Solar System. Some can fall the Earth,
  friction with atmosphere produces fiery streak
  across the sky (most are about the size of a sand
  grain!). Larger ones reach the Earth. Most are
  stony (90 silica, 10 Fe and Ni, similar to mass
  ratio of rock to metal in the Earths mantle and
  core). May reflect primordial composition of the
  Solar system. Some have chondrules which contain
  organic molecules. Some are more metallic. We
  obtain knowledge of the Earths mantle and core
  from meteorites.

47

• Meteorite, believed to be a fragment of the
  asteroid Vesta. Ceres is the largest asteroid
  with a diameter of 930 km.

Fig. 23-29, p.570