Transcript Venus - University of Chicago

Venus
Vital Statistics
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R = 6052 km
M = 4.87 x 1024 kg
Rorbit = 1.082 x 108 km
T = 730º K
Eccentricity = 0.007
Axial tilt = 177.4 º
“day” = -243.0 days
“year” = 224.7 days
orbital inclination = 3.39º
• 0.95 R
• 0.82 M
• 0.72 A.U.
A bit of background
• Known since prehistoric times
• Brightest object in the sky except for the
Sun and the Moon
• It was often thought to be 2 separate bodies
- the morning star and the evening star - but
the Greeks knew better
• Galileo observed phases of Venus
Visibility
Claims to fame
• Earth’s sister planet: only slightly smaller
than Earth; few craters  young surface;
densities and chemical comps similar
• Hottest planet in the solar system
• one of the 4 main pieces of evidence
Galileo presented to support the helocentric
model
• brightest planet in seen from Earth
• rotates “backwards”
Visits
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Mariner 2 - 1962
Pioneer Venus
Venera 7 (Soviet) - 1st spacecraft to land
Venera 9 - returned first photos of the surface
Magellan - 1st orbiter, produced detailed surface
maps using radar
• Venus Express - ESA - now in orbit
• more than 20 total, so far
Mariner 2
• 1st probe to fly by Venus - 1962
• measured temperature of 800 F, now revised
to 900 F
• cloud-covered atmosphere composed
primarily of carbon dioxide
Pioneer Venus
• Inserted into an elliptical orbit around Venus on
Dec. 4, 1978
• flat cylinder 2.5m in diameter and 1.2m high
• All instruments on the forward end
• total mass of 45 kg
• 17 experiments…
• fuel ran out, fell toward Venus, and burned up in
atmosphere in August 1992
Pioneer Venus
Pioneer Venus
• a cloud photopolarimeter to measure the vertical
distribution of the clouds
• a surface radar mapper to determine topography and
surface characteristics
• an infrared radiometer to measure IR emissions from the
Venus atmosphere
• an airglow ultraviolet spectrometer to measure scattered
and emitted UV light
• a neutral mass spectrometer to determine the composition
of the upper atmosphere
Pioneer Venus
• a solar wind plasma analyzer to measure properties of the
solar wind
• a magnetometer to characterize the magnetic field at
Venus
• an electric field detector to study the solar wind and its
interactions
• an electron temperature probe to study the thermal
properties of the ionosphere
• an ion mass spectrometer to characterize the ionospheric
ion population
Pioneer Venus
• a charged particle retarding potential analyzer to study
ionospheric particles
• two radio science experiments to determine the gravity field
of Venus
• a radio occultation experiment to characterize the
atmosphere
• an atmospheric drag experiment to study the upper
atmosphere
• a radio science atmospheric and solar wind turbulence
experiment
• a gamma ray burst detector to record gamma ray bursts
Magellan
• May 1989 - Oct 1994 (commanded to plunge into
atmosphere)
• very detailed radar maps 98% of surface
• looped around Sun 1.5 times before arriving at
Venus Aug 10, 1990
• high-res gravity data
• imaged in strips
• repeat scans of some strips
– “look angle” was different in different
scans - allowed construction of 3-d images
Venus Express
• Venus Monioring Camera
• Analyser of Space Plasma and Energetic
Atoms
• Planetary Fourier Spectrometer
• V/UV/NIR mapping spectrometer
• Venus Radio Science Experiment
• UV and IR Atmospheric Spectrometer
Atmosphere
• Surface pressure is 90 atmospheres (about
the same as the pressure at a depth of 1 km
in Earth’s oceans)
• mostly CO2
• Several layers of clouds many km thick
composed of sulfuric acid (the acid in acid
rain)
• runaway greenhouse effect (temperature at
the surface is hot enough to melt lead)
Atmosphere
Atmosphere
Structure
Surface features
• Probably had large amounts of water, but it
has since boiled away
• still volcanically active
• pancake volcanoes - eruptions of very thick
lava
• coronae - collapsed domes over large
magma chambers
• large shield volcanos
Surface features
• no small craters - small objects burn up in
atmosphere
• craters come in bunches, indicating that
meteors break up in atmosphere
• arachnoids - molten rock seeping into
surface features?
• “graph paper” - faults or fractures?
Pancake volcanoes
Shield volcanoes
Sif Mons
Selu corona
Arachnoids
Aphrodite Terra
Ridges indicate repeated compression and
buckling. Dark areas represent regions that
have been flooded by lava
Lava flows - cracks in Venus’
surface
“Graph
paper”
fainter lines
are spaced at
about 1km
Photo from surface
3-d maps
of
surface
(Lakshmi
Ishtar
terra)
3-d maps
of
surface
(Gula
Mons
and
Eistla
Rift)
Terrain map