The Terrestrial Planets Mercury

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The Terrestrial PlanetsMercury
2
Early Drawings of Mercury
3
Phases of an Inferior Planet
4
Sizes of Mercury Venus with Phase
5
Mercury Some Numbers

• Orbital semi-major axis 0.39 AU
• But eccentricity is 21 so
• Perihelion distance 0.31 AU
• Aphelion distance 0.47 AU

• Diameter is 0.38 x Earths
• Mass is 0.06 x Earths
• Surface gravity is 0.38 x Earths
• Uncompressed Density is 5.4 gm/cm3
• compared with 4.2 gm/cm3 for Earth

• Temperature
• Midnight 173 C (-280 F)
• Noon 330 C (620 F)

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Mercury Some More Numbers

• Spin axis tilt is 0o thus, Mercury has no
  seasons

• Schiaparelli thought rotation revolution
• synchronized 11 (like Earth Moon)
• Arecibo radar showed Prot 59 days
• Prev 88 days
• Prev/ Prot 3/2

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Mercury 32 Spin-Orbit Resonance
T 59d
T 0
T 88d
Sun
noon
midnight
88 Earth-days elapsed from noon to midnight, thus
one Mercury-day equals 176 Earth-days or two
Mercury-years.
T 29.5d
8
Mercury(Mariner 10 - March 1974)
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Mercury (Tolstoy Quadrangle)
1500 km
10
Mercury(Caloris Basin)
700 km
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Mercury (Weird Terrain)
100 km
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Mercury (With prominent scarp)
200 km
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Mercury Surface Features

• Heavily cratered Craters named after artists
  authors

• Intercrater Smooth Plains imply
  post-cratering lava
• flows analogous to lunar maria but not
  dark lava

• Caloris Basin opposite Weird Terrain

• Scarps imply planetary contraction

• High density implies huge metallic core, but
  magnetic
• field is very weak (0.5 that of Earth)
• Interior too cool for any liquid region of core
• Mantle may have been blasted away by impact

• No permanent atmosphere
• Sodium, potassium and helium outgas from
  interior

• Pole is highly radar reflective
• No Spin axis tilt, so constant T at poles
• Water ice may be deposited there! Ancient or
  comet infall?

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The Terrestrial PlanetsVenus
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Early Drawings of Venus
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Transit of Venus1882(Next Venus Transitis on
June 6, 2012 The next after that is in 2117
2125)
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Venus Some Numbers

• Orbital Semi-major Axis 0.723 AU
• Eccentricity is small (0.7) so
• Perihelion distance 0.718 AU
• Aphelion distance 0.728 AU

• Diameter is 0.95 x Earths
• Mass is 0.82 x Earths
• Surface gravity is 0.91 x Earths
• Uncompressed Density is 4.2 gm/cm3, essentially
• the same as Earths
• Earths twin? The resemblance stops here!

• Period of Revolution 225 Earth-days
• Period of Rotation -243 Earth-days
• Very close to synchronous with inferior
  conjunction
• Retrograde rotation implies impact spin reversal

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The Venusian Atmosphere

• Chemical Composition
• 96 CO2, 3.5 N2, 0.5 consists of H2O, H2SO4,
  HCl HF
• High altitude cloud layers are H2SO4
• Whatever water may have existed has been
  converted to sulfuric acid

• Highest cloud layers at elevation of 65 km
• compared with 16 km on Earth
• Air is clear below about 33 km

• Surface Pressure 1,350 lbs/in2 or 93 times
  that
• at Earths surface
• Equivalent to being 3,000 ft deep in the ocean

• Atmosphere rotates once every 4 days around
  Venus
• Produces a Venusian jet stream of 400 km/hr
• Solar heating slow surface rotation allow
  this

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Venus Greenhouse Effect
Sunlight heats atmosphere surface
Lower atmosphere surface Try to cool by
emitting IR radiation, but CO2
absorbs it, heating up atmosphere
further
CO2-rich Atmosphere
Venusian Surface
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Venus Greenhouse Effect

• Runaway Greenhouse Effect
• CO2 could be dissolved in Venusian oceans (if
  it had any!)
• High surface temperatures drive CO2 out of rocks

• Net Effect Increases Surface Temperature by
  300o C
• Surface temperature is 750 K (or 900o F)
• Solar systems hottest planet
• Hot enough to melt lead

• Could This Happen to Earth?
• CO2 represents only 0.03 of atmosphere
• But sufficient heating of carbonate rocks could
• potentially increase this by a factor of
  gt105
• Global warming does appear to be occurring
• Is it natural or man-made?

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Spacecraft Visits to Venus

• 22 Missions since the early 1960s
• Most visited planet

• Soviet Venera Program
• Veneras 4 16 attempted to explore
• Venus atmosphere surface
• Measured chemistry properties of atmosphere
• and sent back TV images of surface
• Vega spacecraft dropped balloon probes into
• atmosphere on way to rendezvous with
  Comet Halley in 1986

• American Mariner Program
• Mariner 2, 5 10 with latter sending back
  images of cloud tops
• Pioneer Venus in late 70s and 80s provided
  first radar maps
• Magellan radar mapped 98 of planetary
  surface between
• 1990 and 1994
• Most significant Venus mission to date

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VenusMariner 10February 1974
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Pioneer VenusOperated between Dec 1978 and Aug
1992
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Pioneer Venus MultiprobeMeasured
Atmospheric Properties
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Venus Images from Pioneer-Venus and Hubble Space
Telescope
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Venusian Surface Landings (Veneras 9 10)
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Venera 13 Lander1 March 1982 Survived 127 min.
measured T 457C 855oF P 84 Earth Atmos.
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Venusian Surface (Venera 13 - March 1982 left
right images)
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Arecibo Observatory1000-ft Antenna in Puerto Rico
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Robert C. Byrd Telescope Greenbank, West Virginia
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Arecibo-Greenbank Radar Interferometry Image of
Venus (2001)
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VenusMagellan Radar Imaging SpacecraftOctober
1991
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Magellan Hemispherical View of Venus (Color
Coded to Show Elevation Above Mean Planetary
Radius)
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Venusian Topography I.
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Venusian Topography II.
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Magellan vs. Venera Resolution
Magellan 1991
Venera 1980
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Venus (Alpha Regio)
1300 km
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Venus (Crater Dickinson)
70 km
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Venus (Estla Region Volcanos)
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Volcanoes on Flank of Maat Mons
90 km
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Venus (Maat Mons)
10,000 ft
42
Venus (600 km Channel)
43
Venus (Volcanic Pancakes)
44
Venus (Volcanic Corona)
45
Venus Surface

• Lightly cratered - Craters are young and
  fresh
• Atmosphere protects surface from small impacts
  no regolith
• Craters show extensive ejecta fields
  atmosphere leads to ground-
• hugging flows

• 80 of surface is basaltic lowlands

• Two continents - Aphrodite Terra Ishtar
  Terra
• Associated with volcanic hotspots
• No indicators of lateral plate tectonics as on
  Earth
• Smaller uplifts are called tesserae

• Very extensive surface volcanism
• More than 2,000 volcanic land forms identified
  by Magellan
• Coronae, pancake domes, lava flow fields,
  sinuous
• lava channels, steep sided domes, etc
• More than 140 shield volcanoes larger than 100
  km in diameter

• Surface is 300 to 700 million years old
• Much younger than moon and a bit older than
  Earth surface

• Surface may be remade every half-billion
  years by
• global volcanism

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Where is Venus Magnetic Field?

• No magnetic field has ever been detected

• Even slow rotation would produce one if
• there were a liquid core

• Thus, we conclude there is no liquid core

• But why, Venus is about the same size as Earth

• Maybe periodic global volcanic catastrophes
  have
• cooled Venus interior more efficiently

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Venus Evolution

• Stage 1 - Formation
• Formed slightly closer to sun than did Earth
• Differentiated into silicate mantle and Fe core
  but no magnetic
• field

• Stage 2 Era of Impacts
• Suffered like other planets for several hundred
  million years
• No sign of these early impacts remain today

• Stage 3 Surface Lava Flooding
• Surface basalts resemble those on Earth
• Lavas are global in nature

• Stage 4 Continuing Surface Evolution
• No lateral plate tectonics as on Earth
• Crater density and sizes indicate youth in
  comparison with moon
• Surface may overturn volcanically every half
  billion years or so
• Outbreak of volcanic activity could increase
  greenhouse effect
• raising temperature by 180oF, softening
  crust even further