- a) MASS
0.82 M
b) DIAMETER
0.95 R
c) AVERAGE DENSITY
About the same as Earth's
d) SURFACE GRAVITY
0.9 g
e) ROTATIONAL PERIOD
243 Earth days (very slow)
retrograde rotation -- spins from East to West!
- i) HOW WE KNOW ABOUT THIS STRANGE ROTATION
- 1) DOPPLER SHIFT
Doppler shift is the change in wavelength of the light from an object, due to object moving towards/away from an observer.
| Dl/l = v/c |
where v = speed of light source, c=speed of light, Dl = amount of wavelength "shift", l = wavelength of an emission/absorption line, if the light source were at rest.
2) WHAT WE SEE WHEN WE TAKE A SPECTRUM OF VENUS
By observing which side of Venus is blue-shifted and which is red-shifted, we can conclude that it is rotating in a direction opposite that of most of the other planets.
The small amount of red/blue-shift tells us that it is slowly rotating.
f) ORBITAL PERIOD
225 Earth days
most circular orbit in the solar system
g) SURFACE TEMPERATURE
750 K (hotter than Mercury!!), despite fact that thick clouds reflect 3/4 of the incoming sunlight.
h) SATELLITES
Venus has no moon
B) INTERIOR STRUCTURE
- a) CORE
metallic, partially liquid?, smaller core than that of Earth
b) MANTLE
large rocky mantle
c) CRUST
Made mostly of volcanic basalt
Northern hemisphere ® "highlands" (mountains, plateaus, canyons, volcanos)
Southern hemisphere ® "lowlands" (rolling flat terrain, lava plains), show lots of impact craters.
Radar image generated by Pioneer spacecraft ... So called
"continents" of Venus ("Ishtar Terra"-top, "Aphrodite"-bottom)
There are no small craters, due to thick atmosphere.
Lots of recent volcanic activity (most extensive activity ended perhaps 100 million years ago), but no apparent planet-wide plate techtonic activity.
"Lava domes" as seen by Magellan.
C) HEATING MECHANISMS
Only 3% of the sunlight actually gets through the thick atmosphere to the surface!
Heat on the surface is maintained (and continues to increase) by a runaway greenhouse effect, which is caused by the overwhelming presence of CO2 in the atmosphere.
D) AGE
The surface is fairly young (perhaps a few hundred Myrs)
Taken by Soviet Venera 9 spacecraft, after a soft-landing.
E) MAGNETIC FIELD
No detected magnetic field. Is this the expected answer, given what is known about Venus?
F) ATMOSPHERE
- a) CLOUDS
reach 65 km up (compare to Earth at 16 km!)
Consist mostly of sulfuric acid!
Very strong circulation patterns
b) CONSTITUENTS
96% CO2
3% N
traces of Argon, O, H2O
c) PRESSURE
The atmosphere is so substantial that it produces a very high pressure at the surface ... if you were standing on the surface, you would feel a pressure that is 90 times that felt on Earth at sea-level!
d) EFFECTS ON SURFACE TEMPERATURE
All of that atmosphere serves as a kind of "blanket", keeping the entire planet to within 10K of the same temperature.
G) LIFE
No evidence for either current or past life.
H) EVOLUTION OF THE PLANET
- Earth & Venus probably started out very similarly ... only major difference is that Venus is 30% closer to the Sun.
- Venus, receiving more energy from Sun, is unable to form the large oceans of water that are formed on Earth at the same time, because the water evaporated into the atmosphere.
- Because of a lack of substantial oceans, the carbon dioxide that is in the atmosphere (and is also in the atmosphere of Earth, but is getting aborbed there by ocean and surface rocks, and later by plant life) stays in the atmosphere, causing a greenhouse effect that makes the surface of the planet even hotter ® as the surface gets hotter, the inability of the surface to absorb CO2 is exacerbated (what little ocean there is evaporates even more, releasing whatever CO2 that may have been absorbed), causing additional CO2 to add to the atmosphere, preventing even more of the radiated heat from the planet to escape the surface, making the planet hotter, which causes even more CO2 to be released from surface, adding even more to the greenhouse gasses in the atmosphere, and so on ... ®"runaway" greenhouse.
- The planet is too hot for life to get a foothold, which could have helped absorb some of the CO2 from the atmosphere.
I) MISSIONS TO VENUS
Venera 7-12 (Soviet, 1970-78) - some were landers, others were atmospheric probes.
Pioneer Venus 1-2 (1978) - was an orbiter and lander, resp.
Magellan (1990) - orbiter