ASTR178 Other Worlds

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ASTR178Other Worlds

• A/Prof. Orsola De Marco
• 9850 4241
• orsola.demarco_at_mq.edu.au

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Assignment 2

• Friday September 3, 4PM posted on Blackboard
• Deadline 2 weeks later in the boxes
• Returned October 4, after term break

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The Moon Practical

• If you have not done it, read the unit outline
  wherethere is a link to how to do the practical
  on line.

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In last class the terrestrial planets I

• A few more things about the Moon to finish last
  weeks plan.
• Orbital properties of Mercury (M), Venus (V) and
  Mars (M).
• Naked eye observations, early telescopes (and
  earlytheries) and new observations.
• Spins and rotations and hot to measure them.
• Mercury mystery!
• The terrain of Venus and Mars
• Plate tectonics on Venus and Mars?
• Volcanos on Venus and Mars (and Earth!)
• The atmospheres of Venus and Mars (and Earth!)
• Seasons on Mars
• Evolutions of the atmospheres

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In this class the terrestrial planets II

• Plate tectonics on Venus and Mars?
• Volcanos on Venus and Mars (and Earth!)
• The atmospheres of Venus and Mars (and Earth!)
• Seasons on Mars
• Evolutions of the atmospheres
• Water on Mars
• Life on Mars?

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Why is Mercurys spin period exactly 2/3 of its
orbital period? Tides again!!!
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Venus before the space age

• Average Venus temperature with no atmosphere 40
  C.
• Atmosphere was known possibly keeps the planet
  at a different temperature
• Water Adams and Theodore Dunham (1932) saw CO2
  in spectrum greenhouse!!
• Cloud of Venus reflect a lot (see high albedo)
  maybe that keeps the greenhouse in check.
• Answers have to wait for space probes.

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Venus from space

• Mariner 2 (1962) first successful mission to
  another planet
• It detects microwave radiation and finds Venus
• Hot (gt400 C)
• and Dry

Venera 7 (1970 Russian) first lander, confirms
Venus as a desert searing world (this picture is
actually from Venera 13)
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Mars before the space age
Percival Lowell (American) 1855-1916
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HST image
Viking Orbiter image
Cratered surface. Craters had escaped detection.
Some of the surface of Mars must be very old.
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Mars changing colour due to winds, not seasonal
vegetation changes!
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Topography of Venus (radar altimeter from
Magellan)
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Topography of Mars (laser measurements from the
Mars Global Surveyor)
Highlands are old and cratered, lowlands are
younger and not heavily crated.
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Venus surface

• Venus surface has only 15 the number of
  craters as the lunar maria, indicating an age
  of only 500 Myr.
• There is plenty of evidence for active
• volcanoes and tectonic activity, but that
• activity has stopped.
• It looks like Venus goes through resurfacing
• episodes, or more likely, that the tectonic
  activity is on-going but is distributed evenly.

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• Venus has as much heat as Earth and shouldhave
  tectonic activity.
• Possibly its thinner crust means that the inner
• heat can break the surface more often and more
• evenly. We call this flaketectonics.
• Venus tectonic activity is local, with local
  volcanos and local upwelling, but no large
  scale mountain ranges and ridges.

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Plate tectonics vs. flake tectonics
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• Mars has no earth-like plate tectonics.
  Thereare no features similar to ridges and
  ranges.
• The crust is 40-70 km thick (on Earth it is
  5-35 km). Too thick to allow plate tectonics.
• It did have tectonicactivity a long time ago
  the Tahrsis rise was a large magma rise, which
  also cracked the crust and made the Valles
  Marineris.

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• Press release 28 August 2010 from Mars Express
  (ESA)
• Orcus Patera (defined but irregular volcanic
  craters)
• Elliptical depression, 380 km long 1800 m rims
• Near Olympus mons
• Created by oblique impact?
• Shaped by plate tectonic (presence of graben)?

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Venusian volcanos

• 10 million years old!
• Present day volcanic activity
• Sulfuric compounds in the atmosphere at the
  0.015 level (which is high comparedto Earth.)

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Volcanos on Mars (and Venus) cannot be caused by
subduction. They must be caused by hot spots
(like some volcanos on Earth e.g.,
Hawaii). The lack of plate movement on Mars
means that thevolcano had time to
growhuge. Most volcanos are old butOlympus Mons
is very young, Why?
Olympus Mons 24 km high compare to Mona Loa
(Hawaii) 8 km high
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Venera 13 (Soviet 1981) one of the first landers
Venera 13 measured a temperature high enough to
melt lead and pressures of 90 bars!
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Comparison of the atmospheric structuresof
Earth, Venus and Mars
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Venus clouds have a 4 day rotation speed the
planet has a 243 day spin period. WHY?
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Lets take a look at Mars atmosphere
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Residual ice cap may contain water ice.
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Very fine dust found by Viking 1lander is easy
to lift up and Create dust storms.
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Martian dust devils
Caused by warm air rising and carrying dust up in
the air. They are very large on Mars due to the
fineness of the dust, and they can be seen from
orbit.
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Outgassing of CO2 (H2O, N2 and SO2) from
volcanos happened on Earth, Venus and Mars,
originating thick atmospheres
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On Earth
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On Venus
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On Mars
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All terrestrial planetsstart with
heavieratmospheres. Earth liquid water modest
CO2 Venus initial H2O Greenhouse
effect. More heat and no tectonics, so more CO2.
Hence runaway greenhouse Mars H2O froze
and rained to the ground. Temperature
droppedeven more. CO2 remained partly in the
atmosphere (not enough to warm).
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Key Ideas

• Motions of Mercury, Venus, and Mars in the
  Earths Sky Mercury and Venus can be seen in the
  morning or evening sky only, while it is possible
  to see Mars at any time of night depending on its
  position in its orbit.
• At their greatest eastern and western
  elongations, Mercury is only 28 from the Sun and
  Venus is only 47 from the Sun.
• The best Earth-based views of Mars are obtained
  at favorable oppositions, when Mars is
  simultaneously at opposition and near perihelion.

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Key Ideas

• Rotation of Mercury, Venus, and Mars Poor
  telescopic views of Mercurys surface led to the
  mistaken impression that the planet always keeps
  the same face toward the Sun (1-to-1 spin-orbit
  coupling).
• Radio and radar observations revealed that
  Mercury in fact has 3-to-2 spin-orbit coupling
  The planet rotates on its axis three times every
  two orbits.
• Venus rotates slowly in a retrograde direction.
  Its rotation period is longer than its orbital
  period.
• Mars rotates at almost the same rate as the
  Earth, and its rotation axis is tilted by almost
  the same angle as the Earths axis.

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Key Ideas

• Mercurys Surface, Interior, and Magnetic Field
  The Mercurian surface is pocked with craters, but
  there are extensive smooth plains between these
  craters.
• Long cliffs called scarps meander across the
  surface of Mercury. These probably formed as the
  planets crust cooled, solidified, and shrank.
• Mercury has an iron core with a diameter equal to
  about 3/4 of the planets diameter. By contrast,
  the diameter of the Earths core is only slightly
  more than 1/2 of Earths diameter.
• Mercury has a weak magnetic field, which
  indicates that at least part of the iron core is
  liquid.

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Key Ideas

• Comparing Venus and Mars Most of the surface of
  Venus is at about the same elevation, with just a
  few elevated regions. On Mars, the southern
  highlands rise several kilometers above the
  northern lowlands.
• Venus has a thick atmosphere and a volcanically
  active surface. Mars has a very thin atmosphere
  and little or no current volcanism.
• There is no evidence of plate tectonics on either
  Venus or Mars. On Venus, there is vigorous
  convection in the planets interior, but the
  crust is too thin to move around in plates
  instead, it wrinkles and flakes. On Mars, the
  planets smaller size means the crust has cooled
  and become too thick to undergo subduction.

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Key Ideas

• Volcanoes on both Venus and Mars were produced by
  hot spots in the planets interior.
• The entire Venusian surface is about 500 million
  years old and has relatively few craters. By
  contrast, most of the Martian surface is cratered
  and is probably billions of years old. The
  southern highlands on Mars are the most heavily
  cratered and hence the oldest part of the
  planets surface.

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Key Ideas

• The Atmospheres of Venus and Mars Both planetary
  atmospheres are over 95 carbon dioxide, with a
  small percentage of nitrogen.
• The pressure at the surface of Venus is about 90
  atmospheres. The greenhouse effect is very
  strong, which raises the surface temperature to
  460C. The pressure at the surface of Mars is
  only 0.006 atmosphere, and the greenhouse effect
  is very weak.
• The permanent high-altitude clouds on Venus are
  made primarily of sulfuric acid. By contrast, the
  few clouds in the Martian atmosphere are composed
  of water ice and carbon dioxide ice.

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Key Ideas

• The circulation of the Venusian atmosphere is
  dominated by two huge convection currents in the
  cloud layers, one in the northern hemisphere and
  one in the southern hemisphere. The upper cloud
  layers of the Venusian atmosphere move rapidly
  around the planet in a retrograde direction, with
  a period of only about 4 Earth days.
• Weather on Mars is dominated by the north and
  south flow of carbon dioxide from pole to pole
  with the changing seasons. This can trigger
  planetwide dust storms.

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Key Ideas

• Evolution of Atmospheres Earth, Venus, and Mars
  all began with relatively thick atmospheres of
  carbon dioxide, water vapor, and sulfur dioxide.
• On Earth, most of the carbon dioxide went into
  carbonate rocks and most of the water into the
  oceans. Ongoing plate tectonics recycles
  atmospheric gases through the crust.
• On Venus, more intense sunlight and the absence
  of plate tectonics led to a thick carbon dioxide
  atmosphere and a runaway greenhouse effect.
• On Mars, a runaway icehouse effect resulted from
  weaker sunlight and the absence of plate
  tectonics.