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Unformatted text preview: Discussion Questions from Tuesday
Discussion Questions from Tuesday
• How can we see through the clouds of Venus, and what is actually imaged?
• What kind of structures occur in the Venusian crust, how are they distributed, and what do they signify?
• Why did Venus turn out so different from the Earth?
• What does the population of impact craters on Venus suggest about its history?
• Why do we think the pressure and temperature environment on Mars was different in the past from what it is today? Grand Tour of the Grand Tour of the Solar System, Part 3
Mars, Asteroids, and the Jupiter system Discussion Questions for Today
Discussion Questions for Today In what ways are the shield volcanoes of Mars similar to terrestrial shield volcanoes? In what ways are they different? What evidence is there to suggest not only that Mars’ early environment could support liquid water, but that there may have even been an ocean there? What is meant by the term “orbital resonance,” and how does it apply to the distribution of asteroids in the Main Belt? Why do we think some asteroids may have formed from larger, differentiated planetary bodies, while others seem more primitive? Mars
(continued) Annual Atmospheric Pressure Annual Atmospheric Pressure Variations Dunes Polar Regions Rayed Impact Craters
Rayed Impact Craters
Tornabene, et al.,
Olympus Mons shield volcano
18 km above the surrounding plains (Mauna Loa rises 8.8 km above seafloor)
600 km diameter (Circumscribes 2.65 X area of Ohio)
Basal cliff up to 6 km high (landslides)
Young (perhaps still active) Why is it so big? (plume without plates) Tharsis Martian Meteorites
All are igneous rocks of basaltic or ultramafic composition.
SNC = shergottite (basalt or gabbro), nakhlite (clinopyroxenite),
chassignite (dunite), ALH84001 (orthopyroxenite)
Best evidence for Mars origin
is trapped gases Radiometric ages of SNCs are generally very young, less than
The exception is ALH84001,
which has an age of 4.5 b.y. Spirit rover in Gusev crater Bonus question: who took this photo? Humphrey
Humphrey Normative Mineralogy
Hypersthene 31/26/35% 6/13/0% Magnetite 1.2/1.3/1.7% 4.4/4.3/2.6%
(An43/45/40) Extrapolated to 0.3% S,
Molar Fe2+/Fetotal from Mossbauer Apatite TES Surface Type 2
By Dust TES Surface Type 1 Interpretations of Spectral Compositions
TES Surface Type 2
By Dust TES Surface Type 1 Basaltic
Andesitic Bandfield et al., 2000 Basaltic
Andesitic Hamilton et al., 2001 Basaltic
Wyatt and McSween., 2002
Altered Basalt Vastitas Borealis
Asteroids Asteroids: Nature
Asteroids: Nature Asteroid is Greek for "star-like“. Asteroids are small rocky objects that look like stars in
telescopes, except that they move across the sky like planets
and are part of the Solar System.
and Most asteroids are found in the Main Belt between Mars and
Jupiter and in the Kuiper Belt beyond Neptune.
Kuiper Many exist in near-Earth space too and are known as NearMany
NearEarth Asteroids or NEAs. Other smaller populations exist too: Trojans, Apollos, Amors,
Centaurs,… There may be 1,000,000+ asteroids >1 km in diameter. Asteroids: The Main Belt
Asteroids: The Main Belt
• The Main Belt extends from
about 2.2 to 3.3 AU
• Most of the orbits lie at or
near (±10° to 20°) the
plane of the ecliptic
• More than 20,000 Main
Belt asteroids have wellknown orbital parameters
• The number known has
been recently increasing by
a few thousand per year
because of new telescopic
Edge on view Asteroids: The Largest Ones
Asteroids: The Largest Ones 1 Ceres (1801): D = 940 km, a = 2.77 AU Discovered by Guiseppe Piazzi in 1801
Piazzi was searching for a "missing planet" between Mars and Jupiter 2 Pallas (1802): D=540 km, a=2.77 AU 4 Vesta (1807): D=510 km, a=2.36 AU 13 Main Belt asteroids have D > 250 km Asteroids: Size Distribution
Asteroids: Size Distribution
• The number of asteroids of a
given diameter D is proportional
to 1/D2 collisional distribution
• For example:
3 > 500 km
13 > 250 km
hundreds > 100 km
10,000+ > 10 km (?)
Total: >1,000,000 > 1 km (?)
(a model) • Most of the mass is in the largest
• Total mass of all asteroids is
only ~5-10% mass of the Moon Asteroids: Gaps & Resonances
Asteroids: Gaps & Resonances
• Astronomer Daniel
Kirkwood (1886) noticed
that the Main Belt has
gaps in which asteroids
• The Kirkwood Gaps are
resonances with Jupiter’s
orbit occur, i.e., where
disturbances by Jupiter
are the strongest.
• May explain why no
planet there: Jupiter only
allowed small bodies to
coalesce and prevented
a larger planet from
forming. Asteroids: Other Groups
Asteroids: Other Groups
Trojans 889 asteroids leading and trailing Jupiter by 60° Centaurs 67 asteroids found between Jupiter & Neptune Kuiper Belt Objects More than 400 large asteroids beyond Neptune NearEarth Asteroids (NEAs)
103 Atens: orbits interior to Earth's
593 Apollos: orbits that cross Earth's
595 Amors: orbits exterior to Earth's (e.g. 433 Eros) All these populations remain incompletely inventoried. Asteroids: NEAs
Thousands of NEAs have been discovered through recent surveys. Asteroids: Composition
Asteroids: Composition Spectroscopy and radar observations of asteroids reveal four main classes: C Type: dark, "carbon rich", albedo ~5% D Type: dark, very red spectra S Type: brighter, “stony", albedo ~20% M Type: rare "metallic" type, very radar bright
C,D,S Types are possibly all primitive.
M Types and other anomalous classes might be from differentiated parent bodies.
Much debated. Asteroids: Spectral Distribution
Composition varies systematically with distance from the Sun.
Suggests that asteroids might preserve the conditions of planetary
formation in the Early Solar System. Asteroids: Geology
Asteroids: Geology 4 asteroids visited up close by spacecraft 951 Gaspra: Galileo flyby in 1991 243 Ida: Galileo flyby in 1993 253 Mathilde: NEAR flyby in 1997 433 Eros: NEAR orbital mission in 20002001 Also: Spacecraft images of Martian moons Phobos and Deimos: captured asteroids? Abundant evidence for impacts, and surprising evidence for erosion and tectonism on these small bodies 951 Gaspra
16 x 11 x 10 km 243 Ida
60 x 25 x 19 km Dactyl
D = 1.5 km 253 Mathilde
66 x 48 x 46 km (large!)
Many large craters
Density only 1.3 g/cm3
May be 50% "empty" 433 Eros (2 views)
31 x 13 x 13 km
Many large craters
Density about 2.6 g/cm3 433
As seen by the
NEAR (NearEarth Asteroid
Tectonics: Eros may have been compressed
and possibly even twisted during its history... Last image from NEAR before its
landing: very fine-grained regolith.
Rock is ~4m across Fine-grained regolith appears to be
moving downhill on Eros: erosion. The Dawn Mission
• Launched in 2007
• Arrives at Vesta in October ‘11, leaves in May ‘12
• Arrives at Ceres in Aug ‘15
• Will map the chemical and mineral composition, morphology, topography, etc. of these two very different large asteroids. Outer Planet Satellites
Outer Planet Satellites Gas Giant Satellites
Gas Giant Satellites
Jupiter Medium Satellites
0 Small Satellites
24 Saturn Large Satellites
4 Galilean Satellites
Titan 6 23 Uranus 0 5: 16 Triton M,A,U,T,O
0 7 Neptune 24 23 16 • Distinct and important differences in density, composition, and orbital properties Jupiter System: The Galilean Satellites
Io Volcanically active No H2O! Rock Differentiated.
Europa Smooth icy crust “Ocean” suspected beneath Ice, Liquid Water (?), and Rock Differentiated.
Ganymede Tectonic grooves Ice and Rock Differentiated Magnetic field!
Callisto Battered by impacts. Ice and Rock. Only partially differentiated Io Io: Tidal Heating
Io: Tidal Heating
Io is in synchronous rotation around Jupiter (always shows the same side to Jupiter) and is
stretched into a football shape along the Jupiterpointing axis. Because Io’s orbit is eccentric,
this football shape is not constant but waxes and wanes (flexes) as the gravity differential changes
along Io’s orbit. This flexing heats Io’s interior by shear friction. The situation is prevented from
damping out (Io’s orbital eccentricity is maintained) by resonances with Europa and Ganymede. Io: Volcanic Activity
Plumes such as the one below
imaged along the limb of Io
provide clear evidence that
Io is volcanically active. Io: Volcanic Activity
Io’s surface is devoid of impact
craters and must therefore be
very young. Resurfacing (renewal
of the surface) is very active on Io.
The multicolored deposits on Io are
due to various sulfurrich compounds
emplaced by Io’s volcanic activity.
Bright white deposits are due to SO2
(sulfur dioxide) frost.
There is no evidence for H2O on Io. Io’s initial endowment in H2O must now
be gone. The H escaped and the O recombined with sulfur S to form SO 2. Io: Volcanic Activity
Io: Volcanic Activity Between 1979 and 1981: patterns of volcanic deposits clearly changed as well. Io:
As a result of
on a global scale.
When viewed in
the thermal IR,
active hot spots.
They are sites of
ongoing activity. Io: Volcanic Activity
Io: Volcanic Activity
Io has lakes
of SO2, and
H2O has been
not volcanoes. Europa Europa: Flatland
Europa is the second Galilean Satellite outward from Jupiter (after Io).
On a global scale, Europa’s surface is extremely smooth and flat. Europa has varied surface textures all consistent with a fractured icy crust. Europa: Ice Rafting Tectonics
Europa: Ice Rafting Tectonics Europa’s surface patterns were likely formed
by multiple episodes of a floating ice crust splitting, colliding, grinding, and rewelding
over an “ocean” of fluid material, liquid H2O? Europa: Refrozen Ice Rafts Image showing ~100 km strip of Europa’s surface, acquired by NASA’s Galileo spacecraft. Europa: A Subsurface Ocean ? Beneath Europa’s icy crust, there may be an ocean of liquid water or slush. Europa: Is there Life?
Two key lines of evidence make Europa a possible habitat for Life:
1) Morphologic + Theoretical evidence for sustained presence of liquid H2O.
2) Spectral evidence for the presence of reddish, possibly organicrich, salts. Ganymede Ganymede: Craters & Tectonics
Ganymede: Craters & Tectonics Ganymede is the largest moon in the Solar System. Larger than Mercury!
Surface was shaped by impact cratering and some form of tectonic activity. Ganymede: Ancient & Young
Ganymede: Ancient & Young
Grooved terrain is sparsely cratered: younger than heavily cratered terrain. Callisto Callisto: Impact Cratering
Callisto: Impact Cratering
An extended record of impact cratering is preserved on Callisto, from ancient
basins (e.g., Valhalla) to relatively young crater chains (impacts a la SL9?). The Valhalla Basin was formed by a giant impact early in Callisto’s history.
The impact left a set of concentric wavelike structures in the moon’s icy crust. Galilean Satellites: Interiors
Galilean Satellites: Interiors The relative abundance of H2O ice increases with radial distance from Jupiter. Discussion Questions for Today
Discussion Questions for Today In what ways are the shield volcanoes of Mars similar to terrestrial shield volcanoes? In what ways are they different? What evidence is there to suggest not only that Mars’ early environment could support liquid water, but that there may have even been an ocean there? What is meant by the term “orbital resonance,” and how does it apply to the distribution of asteroids in the Main Belt? Why do we think some asteroids may have formed from larger, differentiated planetary bodies, while others seem more primitive? ...
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- Spring '11