Terrestrial Planetary Geology: Venus

1
Terrestrial Planetary GeologyVenus
2
VENUS Earths (nearly) Twin Sister

• With a hot, crushing, acidic atmosphere, its not
  a top vacation destination!

3
Basic Venusian Data

• Mass is 0.815 Earths (via artificial satelites)
• Radius is 6052 km or 0.95 of Earth (via
  angular diameter at conjunction) Density is 5.2
  g/cm3 or 0.94 of Earth.
• As seen from Earth
• Venus's surface is invisible in the visible band
  completely cloud shrouded.
• Always within 47 degrees of the Sun greatest
  elongation, so NEVER seen more than about 3 hours
  after dusk or 3 hours before dawn (I.e. never at
  midnight here).

4
Venuss Orbit
5
Views of Venus
Brightest object in the sky after the Moon. UV
markings on clouds show fast rotation.
6
Venus Rotation and Year

• Radar measurements from Earth showed very slow,
  retrograde (backwards) rotation
• rotational period (or sidereal day), R -243.0
  days even longer than the orbital period, P
  224.7 days combine for solar day, D -116.7
  days.
• If we define angular speeds in degrees/day, the
  rotation speed is 360/R and the revolution speed
  is 360/P.
• A solar day passes when the spin laps the
  orbit --- goes another 360 degrees 360/D

7
Relation between Days and Year

• This immediately leads to
• Note if P gtgt R (as for Earth) then D ? R (solar
  day just a little longer than sidereal day)
• But, if P R (as for Moon), D ?, implying
  synchronicity (Moons day its year).

8
Venus SLOW RETROGRADE Spin
9
Venus as Seen from Earth Space

• Radar from Earth could also reveal crude
  topography
• the relative elevation of large portions of the
  surface via reflection times relative
  roughness of the surface via reflection
  strengths.
• SPACE MISSIONS HAVE TOLD US MUCH MORE, via
  DETAILED RADAR MAPING Venera
  (USSR), Mariner 10 11, Pioneer Venus
  Magellan (USA)
• Two continents Ishtar Terra, Aphrodite Terra
  (but only about 8 of surface area) lowlands
  have modest elevation changes compared to
  Earth but Maxwell Montes rises 14 km above
  lowest depressions.

10
Radar Images from Orbiters

• Pioneer Venus mosaic, w/ Ishtar Terra (top) and
  Aphrodite Terra (bottom)--blue low, red high
• Magellan, w/ Aphrodite Terra near middle

11
ACTIVITY ON VENUS

• Many shield Volcanoes are seen via radar images.
• Lots of lava domes and lava flows seen A few
  large upwellings coronae
• Some good evidence for current volcanism Fluctu
  ations in SO2 concentrations radio energy
  bursts -- lightning
• No evidence for tectonic motions.
• Many craters, many the calderas of dead
  volcanoes.
• Impact craters too, but lots fewer than Mercury
  or Moon and none smaller than 3 km across
  -- pretty big meteoroids burn up in Venus's atm.
  and sulfuric acid rain and heavy winds ? fast
  erosion.

12
Lava Domes and Lava Flows
13
A Corona and Impact Craters
?Corona Aime 300 km diameter Crater Mead ?280
km diam.
14
Internal Structure

• Probably very similar to Earth, with partially
  molten Fe/Ni core.
• BUT NO MEASUREABLE MAGNETIC FIELD WHY?
• because of much slower rotation, despite likely
  liquid magnetic material. ALSO, a little less
  internal heat and a hotter surface ? less
  convection. So no current tectonic motions,
  despite likely currently active volcanoes.

15
SPACECRAFT LANDED ON VENUS

• Measured atmospheric composition, wind speeds,
  etc.
• 6 VENERA LANDERS came close and 3 landed and sent
  back data.
• They took photographs in (the very low) visible
  light on the surface of Venus and analyzed rocks.
• most basalt (volcanic) some ancient
  granite some sharp edged, ? relatively
  young many small rounded, ? erosion

16
Venera 9 and Venera 14 Photos