PHY 113 Lecture Notes - Lecture 9: Runaway Greenhouse Effect, Ishtar Terra, Solar Time
9 Jun 2018
School
Department
Course
Professor
Chapter 9 Venus
9.1 Orbital Properties
9.2 Physical Properties
9.3 Long-Distance Observations of Venus
9.4 The Surface of Venus
9.5 The Atmosphere of Venus
9.6 Venus’s Magnetic Field and Internal Structure
9.1 Orbital Properties
• Venus is much brighter than Mercury, and can be
farther from the Sun
• Called morning or evening star, as it is still “tied” to Sun, to within ~50 degrees
• Brightest object in the sky, after Sun and Moon partially because it reflects most of its light
Apparent brightness of Venus varies, due to changes in phase and distance from Earth.
Brightest at a thick crescent phase,
9.2 Physical Properties
• Radius: 6000 km – Roughly same as Earth
same as Earth
• Rotation period: 243 days, retrograde
Slow, retrograde rotation of Venus results in large difference between solar day (117 Earth
days) and sidereal day (243 Earth days); note that the solar day is a large fraction of the year,
and the sidereal day is even longer than the year.
This rotation rate is almost a 5:1 resonance with Venus’s closest approach to Earth, which
makes it very difficult to get images of both sides of Venus (from Earth)
9.3 Long-Distance Observations of Venus
Dense atmosphere and thick clouds make surface impossible to see (in visible light)
Early (optimistic) estimates in ~1930s suggested Venus’s surface temperature might be only
10-20 degrees warmer than Earth
Now we know better. Surface temperature is about 730 K— hotter than Mercury!
Even probes flying near Venus, using ultraviolet or infrared, can see only a little deeper into
the clouds
Infrared and radio wavelengths let us penetrate the clouds better!
9.4 The Surface of Venus
Surface is relatively smooth
Two continent-like features: Ishtar Terra and
Aphrodite Terra No plate tectonics
Mountains, a few craters, many volcanoes and large lava flows
Surface of Venus (radio maps from Pioneer and Magellan)
Surface maps
of Venus, with Earth comparison
Ishtar Terra is one of two continent-sized features on the surface of Venus; contains features
such as impact craters
The other is Aphrodite Terra. Notice the ridge lines indicate compression / buckling of
surface.
Dark areas flooded by lava upwellings
Lava (dark) has flowed from cracks on the surface
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Apparent brightness of venus varies, due to changes in phase and distance from earth. 9. 2 physical properties: radius: 6000 km roughly same as earth same as earth, rotation period: 243 days, retrograde. This rotation rate is almost a 5:1 resonance with venus"s closest approach to earth, which makes it very difficult to get images of both sides of venus (from earth) Dense atmosphere and thick clouds make surface impossible to see (in visible light) Early (optimistic) estimates in ~1930s suggested venus"s surface temperature might be only. Surface temperature is about 730 k hotter than mercury! Even probes flying near venus, using ultraviolet or infrared, can see only a little deeper into the clouds. Infrared and radio wavelengths let us penetrate the clouds better! Mountains, a few craters, many volcanoes and large lava flows. Surface of venus (radio maps from pioneer and magellan)
