1. Terrestrial Planetary Geology: Venus

2. VENUS: Earth’s (nearly) Twin Sister
With a hot, crushing, acidic atmosphere, it’s not a top vacation destination!

3. Basic Venusian Data Mass is 0.815 Earth’s (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. Venus’s 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 = days even longer than the orbital period, P = days; combine for solar day, D = 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 >> 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 (Moon’s “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: Fluctuations 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.
Start here on 11/5/09

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