Venus

VenusEarth’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

Venusglobal properties

albedo = 0.65mass = 0.815 of Earth’sdiameter = 0.95 of Earth'sdensity = 5.3 gm/cm3 surface gravity = 0.91 Earth’saxial tilt = 177.3 deg.ORBIT:

0.72 AU = semi. axis0.0068 = eccentricity3.4 deg = inclination224.7 day = period “false color” image

in UV

1962: Carpenter & Goldstein (US) used radar "echoes“ to study Venus’

surface

"double" inverse square problem

RADAR: “Radio Detection and Ranging”

Arecibo Observatory in Puerto Rico

Mapping the Surface via RadarVenus is the most thoroughly mapped of any

planet

movie98% of the surface has been mapped to 100 meters

resolutionOver 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 VenusNearly 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 VenusSapas Mons (radar image)

~ 400 km (250 miles) 2 lava-filled calderasLava flows

Volcanic Features on

Venus

Baltis Vallis: 6800 km long lava flow channel (longest

in the solar system!)

Coronae: Circular bulges formed by volcanic activity

Aine Corona

Lava flowsPancake Domes:

Associated with volcanic activity forming coronae

Some lava flows collapsed after molten lava drained away

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 RegioVertical 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 double-ring.

Effects of a Hot SurfaceImpact 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 Mons3 km tall volcano

Maat Mons 8 km tall volcano with lava flows

extending hundreds of km

1962-1994: Spacecraft to VenusUnmanned 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 Channels1-2 km wide and at least 100’s of km

long

12 km diameter crater

Baltis Vallis Longest channel in solar system: 6800 km long

and 1.8 km wideLo Chen Vallis

How Does Venus Release Its Heat?

Volcanic plumes instead of plate tectonics?Arachnoids

Circular features with concentric rings & fractures with diameters 50-

230 km

CoronaeCircular troughs around volcanic

plateausCould the troughs be subduction

zones?

Artemis Corona2000 km diameter

6 km from rim to trough528 km across

The Surface as Imaged by Venera 14 Composition: volcanic basalt

These surface probes typically survived about one hour

The Surface of VenusEarly radar images already revealed mountains, plains, craters.

Venera 13 photograph of

surface of Venus:

Colors modified by clouds in Venus’

atmosphere

More details from orbiting and landing spacecraft:

After correction for atmospheric color

effect:

Atmosphere96.5% 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 volcanoesNighttime side of Venus in

false-color 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)

Extremely high surface temperature up to 745 K (= 880 oF)

Very efficient “greenhouse”!

“Greenhouse Effect”Venus is the hottest planet and has the densest

atmosphere1950's: radio wave

emissionsurface temperature:

750 K = 900 F

Venus’ thick CO2 atmosphere keeps the surface hot.

Surface pressure is 100x Earth’sHow many pounds per square-

inch?[same as ~3000 feet under

water]

Sulfuric acid clouds“runaway greenhouse

effect”

No Magnetic Field25,000 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.