In Class:
Question to Ponder
Mercury's diameter is about 5000 miles. If one night you measure its
angular size to be about 0.003 degrees, how far away is it?
- a) about 50 miles
- b) about half a million miles
- c) about 10 million miles
- d) about 95 million miles
- e) about 250 million miles
Venus: Earth's Sister Planet?
- Similar size (94% of Earth's radius).
- Similar mass (80% of Earth's mass).
- Similar orbit (nearly circular w/ r = 0.7 A.U.).
- Rocky surface w/ moderate-sized iron core.
Where Venus Went Astray
- Unlike Earth, it's hot (900 F) and dry.
- Runaway greenhouse effect due to very thick atmosphere (96%
CO2).
- High cloud deck of sulfuric acid droplets -- opaque, so we can't
see down to the surface in the optical.
Imaging with Radar
- Magellan spacecraft launched in 1993.
- Uses radar from orbit to measure altitude of the surface, and
creates a topographic map.
- Mapped 98% of the planet at a resolution of ~100 m.
The Surface of Venus
- Mainly a big plain covering 60% of the surface.
- Two large-ish continents -- Ishtar Terra and Aphrodite Terra.
- Other, smaller mountain features.
- No evidence for plate tectonics.
- Many of the mountains appear to be built by volcanic action.
The Mystery of the Craters
- Like all of the terrestrial planets, Venus has craters on its
surface.
- However, the crater density (i.e., number of craters per are on
the surface) is much lower than on Mercury or the Moon.
- Some smaller impactors might have burned up in Venus' thick
atmosphere, but large impactors should have gotten through, and even
after accounting for the atmosphere's effects, there are too few
craters on Venus.
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