Download Fig. 23-CO, p.548

 Chapter 23:
Planets and
their Moons
 Artists concept
of Saturn sized
planet orbiting
a distant star
(detected by
astronomers).
Fig. 23-CO, p.548
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 Sun’s 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.
The planets
*Terrestrial planets:
Mercury
Venus
Earth
Mars
*Jovian planets:
Jupiter
Saturn
Uranus
Neptune
and…….Pluto
(dwarf planet)
Table 23-1, p.552
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
Questions
 Describe implications of Mercury’s lack of both an
atmosphere and hot interior.
 Describe implications of greenhouse gases and a cool
interior on Venus.
 Describe implications of the Moon’s 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).
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);
Fig. 23-2, p.553
*Blob Tectonics? Surface too hot and plastic/or lithosphere too thick?
 The
volcano
Maat Mons
on Venus,
Lava flows
in
foreground.
 Image from
Magellan
Spacecraft.
Fig. 23-3, p.554
Map of Venus
Lowland in blue; highlands in yellow and red-brown.
Fig. 23-4, p.554
The Moon
1600s Galileo named the
plains maria (for seas)
because he thought they
were oceans.
Heavily cratered.
Fig. 23-5, p.555
*Shows cratered
surface of the
moon.
*In some places
there are craters
within craters.
Fig. 23-6, p.555
 Six Apollo missions answered many scientific
questions about the origin, structure and history of the
Moon.
Fig. 23-7, p.556
 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
 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
 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
 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
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
 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
Fig. 23-10, p.558
size…how?
 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
Martian Atmosphere
 Today the atmosphere is frigid and dry.
Surface temperatures average -60 degrees
C (-76 degrees F) at the equator (ice doesn’t
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.
 Recent research found
layered sedimentary rocks,
iron-rich minerals, salts and
ripple marks. Mars contains
water – as ice – at poles,
and in subsurface soils
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
Fig. 23-12, p.560
stream and lake beds.
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
Fig. 23-14, p.563
– Generates Jupiter’s massive magnetic field
 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
 Galileo’s probe
stopped transmitting
at 130km in at
150oC (300oF) with
650km/hr winds at
22 bars
 Winds likely driven
by heat from below
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 Earth’s 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?).
 Io (left); Europa (right); Voyager spacecraft image. Great
Red Spot shown along with turbulent cloud system.
Fig. 23-15, p.563
 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
 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
 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
Fig. 23-18, p.564
life at the subterranean oceans?
 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
 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
 A close up of young
terrain on
Ganymede shows
numerous grooves
(> 1 km wide).
These grooves may
have formed by
recent tectonic
activity?
Fig. 23-21, p.565
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 Earth’s surface. At these conditions, methane on Titan could act
like water on Earth; there appears to be features caused by flowing liquids.
Titan
 The Cassini-Huygens
spacecraft was launched
during 1997 to study Saturn
and its moons. The
Huygens probe (sent to
study Saturn’s largest
moon: Titan) separated
from the spacecraft (which
arrived at Saturn during
July, 2004) and landed on
Titan’s surface during
January of 2005. Why
study Titan? One reason is
that methane and nitrogen
likely react to form simple
organic compounds.
Assignment (don’t do unless specifically assigned)
 You are presenting a paper at a scientific seminar on Titan
(Saturn’s 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/CassiniHuygens/index.html (could start here).
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
Saturn’s gravitational
field.
Fig. 23-23, p.566
 Voyager I and II planetary spacecraft provided
valuable data on Jupiter, Saturn, Uranus and Neptune.
Fig. 23-24, p.567
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 Neptune’s 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
 Data shows Pluto is the smallest planet (reclassified as dwarf
planet during 2006) in the Solar System (smaller than Earth’s
Moon). It’s 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 (Pluto’s Moon) may be escaped moons from
Neptune or Kuiper-belt objects?
Fig. 23-26ab, p.568
 Never visited by spacecraft, so how
do we know Pluto’s properties?
 During 1978 Charon was
discovered; by measuring Charon’s
orbit, can calculate relative masses
of each.
 From diameter and mass
calculations, Pluto’s 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
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
Comets
below, 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?)
 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). Halley’s comet had
a coma radius of 4500 km when it passed Earth
during 1986.
– Some contain organic compounds
 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
Fig. 23-28, p.570
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 Earth’s 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 Earth’s mantle and core from meteorites.
 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