Venus
Closest
approach to Earth, 25 million miles every 19 mo.
Similar
in size & density to Earth
No
moons
Can
be observed in total darkness; reaches 47' greatest elongation
Brightest
planet: close and highest albedo (0.76) - due to cloud cover
Sulphuric
acid droplets in three layers between 60 km. and 48 km. above surface
Probably
due to S02 from vulcanism
Clouds
move very fast: 360 km/hr in direction of rotation
Rotation
period from radar Doppler in 1961 (earth-based) 243 d sidereal rotational
period - retrograde
Is
longer than its year (225 d Solar day - 116.8 d.
Atmosphere: Mostly C02 (96%), N2
(4%), traces H20 vapor, 02, S02 H2SO4
droplets
Orbiters
and landers of Pioneer Venus & Venera series learned nature of clouds
Surface conditions: 90 atm., 900'F
Greenhouse Effect: high CO2 content - sunlight transmitted
Heats
surface, reradiates as infrared - blocked by C02 .-. heat trapped
Why Venus and Earth Different
A)
Both formed similarly from solar nebula
B)
Both had molten stage - differentiation
C)
Outgassing from interiors - H2 & C02 in early
atmosphere
D)
Earth: O2 from rocks and H2 from atmos. - liquid H2O
oceans - absorb C02
E)
Venus: No liquid H20 (too hot), H20
vapor instead, which
also
holds in infrared higher temps.
F)
Earth: life - photosythesis conversion C02 to 02
G)
Venus: H20 dissociated to H2 and 02; H2
lost to space 0, combined with other elements, e.g., H2SO4
H)
Could it happen on Earth?
Surface: Mapped by Pioneer Venus radar mapper
3
types of terrain:
1)
rolling plains (65%)
2)
highlands (8%): Ishtar Terra, Aphrodite Beta Regio
3)
lowlands (27%)
No
current large-scale tectonic activity (continental drift), but evidence of
stress in crust
Volcanoes
imply convection in mantle does or did exist, but crust did not break up and
move as on earth.
VENERA PROBES - ATOMOSPHERE AND SURFACE:
Venera
1, 1961.
Venera
2, 3 - 1966. Both failed to return data.
Venera
4-8 - ejected capsules into atms. 1967 returned data, were crushed
(4-6).
Venera
7 reached surface (1970).
Venera
8 (1972) surface data.
Venera
9, 10 orbiter and lander first images of surface (1975).
Venera
11, 12 (1978) images color.
ORBITAL RADAR MAPPERS:
Two
Venera orbiters (1983)
2
Km surface resolution
Complemented
mapping by Pioneer 12 (1978) (USA)
Vega
1, 2 (1985) Atms Probes rendezvous with Halley's Comet
Magellan (Aug. 1990) Venus orbit "Synthetic Aperture
Radar" "mosaic" images 530 Km2.
VENUSIAN SURFACE:
Smooth
in general but --- 65% upland plains
Terrae - like continents. Aphrodite Terra, Ishtar Terra, size x
(Africa), size x (USA)
Planitiae - flat lowlands
Regiones - isolated plateaus. Contain mons
(volcanoes)
Montes - mountain ranges
Chasmate - deep channels (chasma)
SURFACE YOUNG:
Several
million 1/2 billion yrs. old.
Maat
Mons - 5 mi high
Volcano
in Aphrodite Terra - lava flows few million yrs. old. Current volcanic
activity? Variations in SO2 over planet suggest so.
Surface features
(slides)
Craters:
volcanic or impact
Impact:
look different - ejecta melts and flows - unique "flower petal".
Cannot "spray" far;
Collisions at 43,000 m/h vaporizes object and
surface
Shock
waves from objects not destroyed in atms. pulverize area surrounding impact
site dark spots (7)
Coronae: (Fotla Corona). 120 mi. diam. Hundreds seen. Blobs
of hot magma rose then sank "fallen souffle'"
Arachnoids: radial cracks from bulging magma blobs raising and
cracking surface
Volcanoes: Maxwell Montes (James Maxwell) 36,000 ft.
Cleopatra crater 60 mi across - on side of Maxwell - impact
"Pancake" domes: sticky lava oozed into wide
puddle 15 mi wide by x 1 mi high. Hundreds of thousands 2-3 Km across seen.