11_Venus - GEL36 SOLAR SYSTEM Lecture 11 Venus(Ch 22 Goal...

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GEL36 SOLAR SYSTEM
Lecture 11: “Venus”
(Ch. 22)
Goal of the Lecture: To discuss the characteristics and history of Venus, including
comparisons of the Venusian atmosphere and surface to the Earth, moon and Mercury.
To illustrate how Venus (and Earth) have climates that are driven by the dynamic
interplay of geologic and atmospheric processes.
Exploration of Venus
Most of our knowledge of Venus has come from the several flybys or orbits by
spacecraft plus numerous probes that have landed on the Venusian surface (mostly by
the former Soviet Union).
- the first spacecraft to visit Venus was Mariner 2 in 1962.
The first spacecraft to land on another planet was from the former Soviet Union,
Venera 7 , in 1975.
NASA had a spacecraft called Magellan orbiting Venus from 1991-94, mapping its
surface by radar (radio waves) that is capable of penetrating the thick, densely
clouded atmosphere.
- when it was nearing its estimated lifetime in 1994, it was ordered to plunge into the
Venusian atmosphere, where it sent back data during its fiery descent.
- Magellan has provided more detailed and complete images of Venus than we have of
our own ocean floor.
Venus Express is a European Space Agency (ESA) mission to study the atmosphere and
plasma environment of Venus. In April 2006 it dropped into a pole-to-pole orbit
around Venus and has sent back detailed pictures. Mission extended to Dec. 2014.
Visit Venus Express to get a summary of the mission and to get ideas for how your
proposal might look – instrumentation you might want to use, what questions you’re
asking, what you hope to learn. (i.e., browse the site to gather more ideas about your
own proposal.)
JAXA (the space agency of Japan) Venus spacecraft (Akatsuki) failed to reach orbit of
Venus in 2010 since it was pulled into the sun’s gravity well. It has to wait 6 years to
try again. Designed to monitor volcanic activity on Venus and provide data on its thick
cloud cover and climate, including whether the planet has lightning.

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Dimensions and orbital characteristics
Roughly the size of Earth, and often called its “sister planet”.
- about 95% of Earth’s diameter and ~80% of Earth’s mass.
- density is 5.2 g/cc (similar to Earth’s) - values indicate mixtures of metal and rock . .
- Venus escape velocity = 10.4 km/sec (vs. Earth’s 11.2 km/sec)
One Venusian year takes 225 earth days (orbital period) and, like the rest of the
planets, orbits in a prograde direction.
One Venusian day takes 243 earth days (period of rotation). Very slow. And unlike most
of the other planets, Venus rotates with a retrograde spin. (sun rises in the west and
sets in the east.) (The sluggish spin may explain the lack of a magnetic field around
Venus. You’ll soon learn that planetary rotation plays an important role in the
development of a magnetosphere.)
- one interpretation of the slow, retrograde spin is that Venus experienced a giant
impact early in its accretion history that reversed its spin and slowed it down.