1) What can we learn about Venus with telescopes on Earth?

Orbit carries it close to Earth •

• thick clouds, surface completely obscured

Measure angular size:

• radar gives distance
• compute diameter = 0.95 x Earth's (similar!)

No moons

Radar enables measurement of "Venus day"

• time to complete one rotation on axis
• why?

Spectra taken with telescopes show:

• thick atmosphere

Much more CO₂ than Earth:

• Venus's surface heats up, stays hot (day& night) 

2) How did we learn more about Venus?

Visit! Unmanned space probes:

• USA (see website):
  • Mariners 2, 5, & 10 (1962, 67, 74)
  • Pioneer (1978)
  • Magellan (1990-4)
• USSR: many!

Flyby and orbiting satellites:

• allow computation of Venus's mass:
• from mass and radius, compute density:

Drop probes into atmosphere (Ex. Pioneer):

• measure composition of atmosphere gases:

• measure pressure of atmosphere gases: •
• measure temperature:
• determine cloud layers:
• measure wind speeds:

3) In what ways is Venus similar to Earth? Different?

Similarities:

• radius (volume, cooling time)
• mass
• density
• has atmosphere
• orbit at similar distance from Sun
• Earth's Twin...

Differences:

• rotating backwards very slowly
• very thick & hot atmosphere

4) Why does Venus have so much more carbon dioxide?

When newly formed, Venus & Earth were probably similar:

• formed at similar region of solar nebula
• similar proportions of iron, rocky minerals, volatiles
• had similar early atmospheres:
• Earth farther from sun, less heat
• Venus closer to sun, more heat

5) What happened to the water Venus did have?

Deuterium (heavy hydrogen: 1p, 1n) unusually abundant on Venus

• suggests there was once lots of H₂O
• hotter temps, so all water stays as vapor high in atm
• Venus has no ozone layer to block out UV rays
• most of water on Venus was destroyed

• Sec. 22-1, starting at "Surface" (pp. 475-483)