Venus
Venus
Earth’s “sister planet”
0.72 AU from Sun
~2x farther from Sun than Mercury
so ~4x less sunlight
~1.4x closer than Earth so sunlight
is (1.4)2 times =~2x more intense
Venus approaches closer to Earth
than any other planet so we should
know a lot about it.
However, its surface is invisible
underneath a thick atmosphere.
“true” color image
Venus
global properties
albedo
= 0.65
mass
= 0.815 of Earth’s
diameter = 0.95 of Earth's
density = 5.3 gm/cm3
surface gravity = 0.91 Earth’s
axial tilt = 177.3 deg.
ORBIT:
0.72 AU
0.0068
3.4 deg
224.7 day
= semi. axis
= eccentricity
= inclination
= period
“false color” image in
UV
RADAR: “Radio Detection and Ranging”
1962: Carpenter & Goldstein
(US) used radar "echoes“ to
study Venus’ surface
Arecibo Observatory in Puerto
Rico
"double" inverse square problem
Mapping the Surface via Radar
Venus is the most thoroughly mapped of any planet
movie
98% of the surface has been mapped to 100 meters resolution
Over 80% of Venus’ surface lies within 1 km of its mean radius
Radar Mapping
Radar Mapping
Radar Map of Venus’ Surface
Surface features
shown in artificial
colors.
Scattered impact
craters
Volcanic regions
Smooth lava flows
Lava Flows
Young, uneven lava flows (shown: Lava flow near
Flagstaff, AZ) show up as bright regions on radar maps.
Surface Features on Venus
Smooth lowlands
Highland regions:
Maxwell Montes are ~ 50 %
higher than Mt. Everest!
Craters on Venus
Nearly 1000 impact
craters on Venus’ surface:
→ Surface not very old.
No water on the surface;
thick, dense atmosphere
→ No erosion
Craters appear sharp
and fresh
Shield Volcanoes
Found above
hot spots:
Fluid magma
chamber, from
which lava erupts
repeatedly through
surface layers
above.
All volcanoes on Venus are shield volcanoes
Volcanism on Venus
Sapas Mons (radar image)
~ 400 km (250 miles)
2 lava-filled calderas
Lava flows
Volcanic Features
on Venus
Aine Corona
Baltis Vallis: 6800 km long
lava flow channel (longest
in the solar system!)
Lava flows
Some lava flows
collapsed after molten
lava drained away
Coronae: Circular bulges formed by
volcanic activity
Pancake Domes:
Associated with
volcanic activity
forming coronae
Lakshmi Planum and Maxwell Mountains
Radar image
Wrinkled mountain formations indicate compression and wrinkling,
though there is no evidence of plate tectonics on Venus.
Surface “Flights”
computer generated images from radar data
Alpha Regio
Vertical scale is exaggerated for
visibility
Impact Craters
About 1000 craters are
located randomly around
Venus.
Venus’s atmosphere is a
shield
very few craters <35 km
diameter
Craters show little
modification by tectonism
or volcanism.
Few craters suggests the
surface is relatively young.
~30 km diameter
Largest crater
is Mead ~280
km diameter
with a doublering.
Effects of a Hot Surface
Impact crater Addams, 90 km diameter.
The surface is so hot that impacts more easily melt
the surface than on other planets.
Outflow of lava extends 600 km away.
Volcanoes & Lava Flows
over 10,000 small shield volcanoes
Gula Mons
3 km tall volcano
Maat Mons
8 km tall volcano with lava flows
extending hundreds of km
1962-1994: Spacecraft to Venus
Unmanned Spacecraft
US:
Mariner 2, 5, 10 flybys
Pioneer Venus orbiter & probes
(1st radar from space)
Magellan (high resolution radar)
Galileo (flybys enroute to Jupiter)
Soviet:
Venera 4-16 (#7,8; 9,10; 13,14
landed)
VEGA 1, 2 (landers & balloons)
Surface map from 10
years of radar data
Lava Channels
1-2 km wide and at least 100’s of km long
Lo Chen Vallis
12 km diameter crater
Baltis Vallis
Longest channel in solar
system: 6800 km long and
1.8 km wide
How Does Venus Release Its Heat?
Volcanic plumes instead of plate tectonics?
Arachnoids
Circular features with concentric rings
& fractures with diameters 50-230 km
Coronae
Circular troughs around volcanic
plateaus
Could the troughs be subduction zones?
528 km across
Artemis Corona
2000 km diameter
6 km from rim to trough
The Surface as Imaged by Venera 14
Composition: volcanic basalt
These surface probes typically survived about one hour
The Surface of Venus
Early radar images already revealed mountains, plains, craters.
More details from orbiting and landing spacecraft:
Venera 13
photograph of
surface of Venus:
Colors modified by
clouds in Venus’
atmosphere
After correction for
atmospheric color
effect:
Atmosphere
96.5% CO2, 3.5% N2 -- no O2 or H2O
also acids: hydrochloric, hydrofluoric & sulfuric
Dark areas are locations of the
sulfuric acid clouds.
Bright areas are gaps between
clouds.
Clouds near equator are fluffy
but those at higher latitudes are
stretched by high winds.
H2SO4 (sulfuric acid) clouds may
come from SO2 outgassing from
active volcanoes
Nighttime side of Venus in falsecolor image from a near-infrared
camera (2.3mm) on the Galileo
spacecraft
The Atmosphere of Venus
UV image
Extremely inhospitable:
96 % carbon dioxide (CO2)
3.5 % nitrogen (N2)
Rest: water (H2O), hydrochloric
acid (HCl), hydrofluoric acid (HF)
4 thick cloud layers (→ surface
invisible to us from Earth).
Very stable circulation patterns with
high-speed winds (up to 240 km/h)
Very efficient “greenhouse”!
Extremely high surface temperature
up to 745 K (= 880 oF)
“Greenhouse Effect”
Venus is the hottest planet and has the densest atmosphere
1950's: radio wave emission
surface temperature:
750 K = 900 F
Venus’ thick CO2 atmosphere
keeps the surface hot.
Surface pressure is 100x Earth’s
How many pounds per square-inch?
[same as ~3000 feet under water]
Sulfuric acid clouds
“runaway greenhouse effect”
No Magnetic Field
25,000 x weaker than Earth’s
Too slow a rotator to generate an
internal dynamo
Perhaps Venus’ lack of crustal
plates inhibits internal convection
currents of molten rocks.