Astronomy 330

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Astronomy 330

• Lecture 13

Image from http//cmex-www.arc.nasa.gov/CMEX/inde
x.html
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Astronomy 330

• Mars is differentiated, it has a mantle and a
  crust in addition to the core we just discussed
• No seismometers have been successfully placed on
  Mars (the ones on the Vikings failed to work
  properly).
• Can anyone think of any reasons why Mars might be
  differentiated?

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Astronomy 330

• Missions to Mars showed many features (craters,
  basins, canyons, volcanoes, plains, )
• Valles Marinaris - large canyon system observed
  on Mars
• Olympus Mons - largest volcano Mars
• Hellas - large impact basin
• Chryse Planitia (Plains of Gold) - plains
  covering much of Northern hemisphere, formerly
  called Chryse Reggio

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Astronomy 330 Vallis Marinaris
http//cmex-www.arc.nasa.gov/CMEX/index.html
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Astronomy 330 Olympus Mons
http//cmex-www.arc.nasa.gov/CMEX/index.html
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Astronomy 330 Lava flows, Olympus Mons
http//cmex-www.arc.nasa.gov/CMEX/index.html
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Astronomy 330 Hellas Basin
http//cmex-www.arc.nasa.gov/CMEX/index.html
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Astronomy 330 Surface Elevations

• Measured using a laser range finder on Mars
  Global Surveyor, accurate to a few meters
• Range in elevations is very large on Mars
• Volcanic Mountains 31 km above lowest region
  (Hellas Basin), (only 20 km on Earth)
• Olympus Mons is about 25 km tall (relative to its
  surrounding plains), on Earth and Venus the
  tallest are only 10 km
• This is the result of the reduced surface gravity
  on Mars, size of a mountain depends on the
  interplay between gravity trying to crush the
  mountain and the strength of the rocks holding it
  up

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Astronomy 330 Question

• The surface gravity on Mars is 2/5 that of the
  Earths
• The surface gravity on the Moon is 1/6 that of
  the Earths
• Why then, arent there REALLY big mountains on
  the Moon ?

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Astronomy 330

• The southern hemisphere of Mars has the highest
  surface elevations and averages about 6 km above
  the northern hemisphere
• The northern hemisphere is also a VERY flat (bed
  of an ancient ocean ???)
• Southern hemisphere is more heavily cratered
  (i.e. older) and also darker
• These features are a mystery!

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Astronomy 330 Overall Martian Topography
http//solarsystem.nasa.gov/multimedia/gallery/MER
_Landings.jpg
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Astronomy 330 Pole to Pole topography
http//cmex-www.arc.nasa.gov/CMEX/index.html
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Astronomy 330

• Tharsis bulge is another major topographic
  feature
• Volcanically active region the size of North
  America
• 10 km in elevation, boundary between southern
  uplands and northern lowland plains
• Least cratered part of surface (why do you think?)

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Astronomy 330 Tharsis Region
http//cmex-www.arc.nasa.gov/CMEX/index.html
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Astronomy 330 Tharsis bulge

• Three large shield volcanoes occur near the
  center of Tharsis bulge
• Olympus Mons (the size of Texas or France) also
  occurs at one edge of Tharsis
• Valles Marineris also occurs here, 4000 km long,
  3 km deep on average, 7 km deep max, width is 500
  km
• All of this seems to be due to a giant hot spot
  that has remained at the same location relative
  to the surface of Mars (no plate tectonics)

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Astronomy 330 Tharsis Bulge
http//cmex-www.arc.nasa.gov/CMEX/index.html
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Astronomy 330 Vallis Marinaris
http//cmex-www.arc.nasa.gov/CMEX/index.html
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Astronomy 330 Craters and Basins

• Concentrated in southern highlands
• Appear similar to Moon craters (rims, flat
  floors, terraced rims, central peaks).
• Densities are much higher than on Earth or Venus
• Indicates very old age for uplands, formed during
  the first billion years of the Solar System.

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Astronomy 330 South Pole of Mars
http//cmex-www.arc.nasa.gov/CMEX/index.html
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Astronomy 330 Martian Highlands
http//solarsystem.nasa.gov/planets/profile.cfm?Ob
jectMarsDisplayGallery
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Astronomy 330 Craters

• Ejecta patterns for Martian craters are different
  with respect to the Moons
• Small, simple craters on Mars appear similar to
  Moons while large craters show large variation
  in characteristics
• On the Moon, surround by rough, hilly terrain,
  radial streaks
• On Mars, smooth ejecta blankets with well defined
  edges, no rays or streaks
• Fluidized ejecta (splosh craters)

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Astronomy 330 A Martian Crater
http//solarsystem.nasa.gov/planets/profile.cfm?Ob
jectMarsDisplayGallery
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Astronomy 330 Crater types

• Flower form - multiple lobed ejecta, several
  layers, each has smooth sharp edge, occur near
  equator (within 40o).
• Pancake - ejecta are smooth with a scalloped edge
• Both types probably formed by fluid debris (ice
  melted by impact (?)) which flowed along surface
  instead of exploding outward
• Also, many large craters (gt 50 km) have smooth,
  flat floors with eroded rimsflat plains
  surrounded by low hills

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Astronomy 330 Craters

• Flower forms and pancakes occur for craters
  between 5 and 50 km in diameter
• These different forms may be caused by the amount
  of water beneath the surface at the site of impact

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Astronomy 330 Flower Form Crater
http//solarsystem.nasa.gov/planets/profile.cfm?Ob
jectMarsDisplayGallery
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Astronomy 330 Pancake Craters
http//cmex-www.arc.nasa.gov/CMEX/index.html
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Astronomy 330 A Large Crater on Mars
http//cmex-www.arc.nasa.gov/science/index.html
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Astronomy 330 Crater Comparisons
http//solarsystem.nasa.gov/planets/profile.cfm?Ob
jectMarsDisplayGallery
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Astronomy 330 A crater close up (Endurance
crater, Opportunity)
http//solarsystem.nasa.gov/multimedia/display.cfm
?IM_ID2963
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Astronomy 330 Basins

• Hellas is largest basin, 1800 km diameter, 6 km
  deep, has a single ring of uplift mountains (not
  multiple like on the Moon)
• Interior covered by dust (deposited by winds)
• Argyre and Galle are other basins
• Lowell crater shows multiple rings, or rims like
  Moons impact basins
• Mars has fewer basins than the Moon, perhaps
  earlier formed basins have been eroded on Mars,
  the Martian crust stabilized later than the Moon
  (expected).

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Astronomy 330 Hellas Basin
http//cmex-www.arc.nasa.gov/CMEX/index.html
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Astronomy 330 Surface Ages

• Cratering models (which assume that a number of
  impacting bodies determined from the Moons
  craters, and take into account the different
  gravity of Mars) show that the oldest terrains on
  Mars are at least 4 billion years old (like the
  lunar highlands).
• Mars has a wide variety of crater densities on
  different surfaces
• Tharsis volcanoes have the newest surfaces, many
  fewer craters than the lunar maria.

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Astronomy 330 Nole and South poles showing
different crater densities. Which is which?
http//cmex-www.arc.nasa.gov/CMEX/index.html
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Astronomy 330 Surface Ages

• Upland crater densities are much higher than the
  maria but less than lunar highlands
• So, uplands date to close to 4 billion years
• Erosion has been (and is) present on Mars, making
  interpretation of crater densities difficult.
• Studying the number of small craters (most
  subject to erosion) in uplands relative to other
  areas shows that there are fewer in the
  uplandsthis implies that erosion was more
  efficient in the far past of Mars.

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Astronomy 330

• Northern plains are much less cratered
• Viking landers seem to indicate a volcanic origin
  for plains
• In northern plains the crater densities are
  similar to maria for small craters, large craters
  are somewhat more numerous than for the Lunar
  Maria

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Astronomy 330 Surface details from Viking and
Pathfinder

• Viking was designed to be an independent
  laboratory on Mars
• Each lander weighed a ton and was powered by
  radioactive electric generator
• Communicated directly with Earth or the orbiting
  spacecraft
• Instruments included cameras, chemical analysis
  devices, meteorological weather station, a
  seismometer (which didnt work), and an arm to
  dig into soil and retrieve samples

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Astronomy 330 Viking

• Also contained instruments to measure atmosphere
  during descent
• X-ray spectrometer
• GCMS (Gas Chromatograph-Mass spectrometer) for
  measuring composition of the atmosphere and
  volatile compounds

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Astronomy 330 Sojourner

• First rover on Mars
• Largely a demonstration project, laid the
  groundwork for current Mars rovers Opportunity
  and Spirit.
• Moved very slowly, was small (12 kg)
• Lander contained cameras and a device for
  measuring the elemental composition of rocks.

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Astronomy 330

• Landing sites chosen for safety for all missions,
  dull flat locations
• No volcanoes or canyons or large impact craters
• Also only low elevations chosen so that
  parachutes would work effectively
• So, lowland planes of the northern hemisphere
  were mostly chosen

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Astronomy 330

• Viking 1 landed in Chryse Planitia (east of
  Tharsus) and landed near the equator
• Viking 2 landed at 44o north to measure seasonal
  effects
• Pathfinder landed at Ares Vallis, near Chryse
  Planitia (landed using airbags)

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Astronomy 330 Viking 1 landing site
http//cmex-www.arc.nasa.gov/CMEX/index.html
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Astronomy 330 Panorama of Viking 1 site
http//cmex-www.arc.nasa.gov/CMEX/index.html
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Astronomy 330 Viking 2 landing site (boring!)
http//cmex-www.arc.nasa.gov/CMEX/index.html
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Astronomy 330 Viking 2 panorama
http//cmex-www.arc.nasa.gov/CMEX/index.html
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Astronomy 330 Pathfinger landing site (Ares
Vallis)
http//cmex-www.arc.nasa.gov/CMEX/index.html
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Astronomy 330 The Surface seen by Pathfinder
http//cmex-www.arc.nasa.gov/CMEX/index.html
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Astronomy 330 What these landers found

• Viking 1 landed in a plain similar in appearance
  to lunar maria with few craters suggesting an age
  of 3 billion years. Surface probably volcanic in
  origin but later flooded by water and eroded by
  wind.
• Lander found a landscape similar to Earths
  deserts, gently rolling topography, many rocks in
  size from golf-ball sized to boulders
• Soil is fine grained and has a relatively hard
  crust, wind-blown dust
• Rocks appear to be volcanic and are probably
  ejecta from craters

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Astronomy 330

• Viking 2 landed in the Utopia plain on ejecta
  from a nearby large crater (Mie, 90 km diameter).
• Many more rocks than at Chryse, also appear to be
  of volcanic origin, heavily pitted

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Astronomy 330

• Pathfinder found a landscape very similar to that
  found by to Vikings
• Some distant hills
• Chemical analysis experiments showed no major
  differences between rocks and all were igneous,
  not basalts
• Analysis of angular appearance of rocks and how
  they were aligned suggested rocks carried by
  water into planes

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Astronomy 330

• Vikings confirmed that red color of Mars is due
  to iron oxides (rust) in the surface soil
• Soil is fine grained dust, transported by wind
  and major storms, deposited over the surface
  obscuring rocks, light in color
• Sojourner showed rocks had a high Silicon
  content, similar to granite of Earths continents
  (this was a surprise because Mars does not show
  plate tectonic activity)
• Dust storms change the reflectivity of the
  surface, this is seasonal and explains old
  telescopic observations

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Astronomy 330

• Sand dunes are seen in many places by orbiters,
  indicating the global nature of the Martian
  winds.
• Martian meteorites (rocks blasted into space by
  impacts, later landed on Earth, gas trapped in
  rocks show a Martian composition) are mainly
  basalts, 1.3 billion years old
• No explanation for why these rocks are basalts
  and rocks observed on Mars are granites.

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Astronomy 330 Sand dunes in Vallis Marinaris
http//cmex-www.arc.nasa.gov/CMEX/index.html
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Astronomy 330 Sand Dunes on Mars Near North
Pole(Inca City)
http//cmex-www.arc.nasa.gov/CMEX/index.html
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Astronomy 330 Yardangs from Mars Express
http//solarsystem.nasa.gov/multimedia/display.cfm
?IM_ID2763
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Astronomy 330 South Pole dust storm
http//cmex-www.arc.nasa.gov/CMEX/index.html
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Astronomy 330

• Martian meteorites appear to be from the upper
  mantle of Mars
• Ratios oxygen isotopes in these rocks are
  different from Earth and Moon, implied Mars did
  not form near Moon and did not participate in the
  impact which presumably created the Moon.
• Rocks also show different oxygen isotope ratios
  of the water in the rocks and the rocks
  themselves. Again, this is different from Earth
  and indicates Mars is less mixed (no plate
  tectonics)

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Astronomy 330

• Viking landers now belong the Smithsonian and are
  actually considered a museum exhibit !!!

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Astronomy 330 Reading

• Read all the material under the links at the
  following WEB site

http//cmex-www.arc.nasa.gov/science/index.html