Chapter Four

Venus - The Veiled Planet

We never "see" Venus' surface - opaque clouds 10 times as reflective as surface of Moon. Yellow clouds of sulfuric acid. Venus has a long day (243 Earth days), even longer than Venus' year (224 Earth days to orbit Sun) (also Venus rotates backwards). Venus only a few perent smaller than Earth, but Venus' surface hot enough to melt lead and zinc. Venus has no detected magnetic field. Venus is closer to Sun than Earth. Venus has a dense carbon dioxide atmosphere-

Venus = 96.4% CO₂
Earth = 0.03% CO₂

Earth atmosphere mainly nitrogen (78%) and oxygen (21%). No water or oceans on Venus. Carbon dioxide in rocks on Earth.

Greenhouse Effect

Visible light to ground.
Heat of ground radiated at infrared wavelengths.
Water vapor and carbon dioxide reflect infrared radiation and trap heat near surface.
Like a leaky bucket with a hole in the bottom or rolled up car windows on summer day.
Earth greenhouse makes surface temperature hotter by T = 30ºK.
Venus CO₂ greenhouse T = 200ºK
.
(for Earth good thing, otherwise oceans would freeze) - but see second half of course for global warming.

Venus' runaway greenhouse-boils oceans away and bakes CO₂ out of rocks. Surface temperature = 730ºK. Earth's carbonate rocks contain as much CO₂ as Venus' atmosphere On Earth mild greenhouse surface 288ºK.

Imaging Venus' Surface
(Not in text. Also read Magellan Images Venus)

Click here to view a radar image of Venus

Radio waves see through clouds.
Radar = Radio defection and ranging (time delay).
Time delay = distance = topography
Brightness = rough or smooth
(No erosion yet smooth - one level of topography, not two like Earth).
Lava flow 500 million years ago wiped the slate clean and smoothed out surface of Venus
Some highlands = Aphrodite Terra (Equatorial) = Ishtar Terra = Plateau ringed by mountains.
Venus - Numes of surface features Goddesses - hunt, fertility, love; and mortal women - now dead, Billie Holiday

Craters on Venus

Not as many craters as on Moon. (Venus' surface 500 million years old)
Uniform distribution of craters. (Global volcanic resurfacing) Crater ejecta - close-high gravity

{ crater flow - atmosphere
hot thick atmosphere = { craters asymmetric

Crater cluster - break up of meteor in atmosphere. No small craters - meteors burn up in atmosphere.

Tectonic Processes on Venus

Tectonics - Greek for building. Caused by internal heat trying to get out. Venuus - up and down. Earth - sideways, plates. Venus' mountains up welling.

Volcanoes on Venus

Magellan - continued (not in text)

Magellan -five - year mission (launched in May 1989, suicide in October 1994). Mapped 98% of surface to resdation of 100 meters - topography, texture, and gravity. Re-entry (or really entry) = aerobraking = August 1993. Used resistance of Venus' thick atmosphere to settle Magellan into a low, circular orbit, instead of its previous high elliptical one.

Gravity measurements -from low circular orbit-maps distribution of underlying mass (which pulls spacecraft and causes small wiggles in its orbit).

Results of Gravity Measurements (not in text)

Venus has a thick, rigid crust. The planet is encased in a thick shell. Earth has thinner crust and a broken shell. Geological structures on Venus are supported by hot plumes of magma including mountains and volcanoes. (the warm rocks of Venus are not as strong as those on Earth because of the heat and perhaps the lack of water.)
Since volcanoes on Venus are now supported by hot rising plumes, they could still be active. (Bright radar reflectivity of volcano tops, like Maat Mons, suggest youth-unweathered - and possible activity).

Other important Magellan results: (not in text)

Volcanoes are everywhere on Venus from shield volcanoes to unique volcanic coronas and arachnoids.
The entire planet was turned inside out and resurfaced about 500 million years ago; surface geologically quiet since then but a few active volcannoes now possible.

	{ crater flow - atmosphere
hot thick atmosphere =	{ craters asymmetric