VenusVenusEarth’s Sister PlanetEarth’s Sister Planet

Venus vs. Earth Venus vs. Earth

Venus and Earth are similar in:Venus and Earth are similar in: SizeSize Density Density Chemical compositionChemical composition Distance from the SunDistance from the Sun FormationFormation

At formation, they must have been almost At formation, they must have been almost indistinguishable from one anotherindistinguishable from one another

They are now about as different as two terrestrial planets They are now about as different as two terrestrial planets can be can be

However, Earth is teeming with life while Venus is an However, Earth is teeming with life while Venus is an uninhabitable infernouninhabitable inferno

Somewhere along their respective evolutionary paths, Somewhere along their respective evolutionary paths, Venus and Earth diverged Venus and Earth diverged

Orbital PropertiesOrbital Properties

Second planet from Second planet from the Sunthe Sun

Always fairly close to Always fairly close to the Sun in the skythe Sun in the sky

Third brightest object Third brightest object in the skyin the sky

You can see Venus in You can see Venus in the daytime if you the daytime if you know where to lookknow where to look

BrightnessBrightness Venus is highly reflectiveVenus is highly reflective Nearly 70% of the sunlight reaching Venus is reflected Nearly 70% of the sunlight reaching Venus is reflected

back into spaceback into space Only 10% of light is reflected off of the Moon and Only 10% of light is reflected off of the Moon and

MercuryMercury Most of the sunlight is reflected off of the clouds high Most of the sunlight is reflected off of the clouds high

in the atmospherein the atmosphere Venus appears full when it is at its greatest distance Venus appears full when it is at its greatest distance

from Earthfrom Earth When Venus is closest to Earth, we cannot see the When Venus is closest to Earth, we cannot see the

sunlit side of the planet at allsunlit side of the planet at all

GizmoGizmo

Radius, Mass, and DensityRadius, Mass, and Density

Radius-3761 miles or 95% of Earth’s Radius-3761 miles or 95% of Earth’s radiusradius

Mass-4.9x10Mass-4.9x102424 kg or 82% of Earth’s mass kg or 82% of Earth’s mass Density-95% of Earth’s densityDensity-95% of Earth’s density

Rotation RateRotation Rate The clouds of Venus made it impossible for us to discern The clouds of Venus made it impossible for us to discern

any surface features on the planet any surface features on the planet Astronomers didn’t know the rotation period of Venus Astronomers didn’t know the rotation period of Venus

until radars were used in the 1960’suntil radars were used in the 1960’s It takes Venus 243 days to rotateIt takes Venus 243 days to rotate The spin of Venus is also retrograde-opposite of Earth The spin of Venus is also retrograde-opposite of Earth

and the orbit of Venusand the orbit of Venus Venus takes 225 days to orbitVenus takes 225 days to orbit

Why is Venus rotating backwards Why is Venus rotating backwards and slowly?and slowly?

At present, the best explanation planetary At present, the best explanation planetary scientists can offer is that early in Venus’s scientists can offer is that early in Venus’s evolution, the planet was struck by a large evolution, the planet was struck by a large body, much like the one that may have hit body, much like the one that may have hit Earth and formed the Moon, and that Earth and formed the Moon, and that impact was sufficient to reduce the impact was sufficient to reduce the planet’s spin almost to zero planet’s spin almost to zero

Observing VenusObserving Venus

Venus has a dense Venus has a dense atmosphere and thick atmosphere and thick clouds that are opaque to clouds that are opaque to visible radiation, making visible radiation, making its surface completely its surface completely invisible from the outside invisible from the outside at optical wavelengths at optical wavelengths

This is one of the best This is one of the best photographs of Venus photographs of Venus taken with a large taken with a large telescope on Earthtelescope on Earth

Observing VenusObserving Venus

Atmospheric patterns Atmospheric patterns are more evident are more evident when looking at when looking at ultraviolet radiationultraviolet radiation

This is an ultraviolet This is an ultraviolet image taken in 1979 image taken in 1979 by the U.S. by the U.S. Pioneer Pioneer VenusVenus spacecraft at a spacecraft at a distance of 200,000 distance of 200,000 km from the planet km from the planet

SurfaceSurface Detailed radar observations Detailed radar observations

have been made both from have been made both from Earth and from the Earth and from the Venera, Venera, Pioneer Venus,Pioneer Venus, and and MagellanMagellan spacecraft spacecraft

This image of the surface of This image of the surface of Venus was made by a radar Venus was made by a radar transmitter and receiver on transmitter and receiver on board the board the PioneerPioneer spacecraft, spacecraft, which is still in orbit about the which is still in orbit about the planet but now inoperative planet but now inoperative

The two continent-sized The two continent-sized landmasses are named Ishtar landmasses are named Ishtar Terra (upper left) and Terra (upper left) and Aphrodite (lower right)Aphrodite (lower right)

Colors represent altitude: blue Colors represent altitude: blue is lowest, red highest is lowest, red highest

TopographyTopography The surface of Venus appears The surface of Venus appears

to be relatively smooth, to be relatively smooth, resembling rolling plains with resembling rolling plains with modest highlands and modest highlands and lowlands lowlands

Mountains comparable in Mountains comparable in height to those on Earth height to those on Earth

The elevated “continents” The elevated “continents” occupy only 8 percent of occupy only 8 percent of Venus’s total surface areaVenus’s total surface area

The remainder of Venus’s The remainder of Venus’s surface is classified as surface is classified as lowlands (27 percent) or rolling lowlands (27 percent) or rolling plains (65 percent)plains (65 percent)

No tectonic plate boundaries No tectonic plate boundaries are evidentare evident

Lakshmi Planum Lakshmi Planum

Great plateau Great plateau 932 miles across at its widest point932 miles across at its widest point Ringed by mountain rangesRinged by mountain ranges Including the Maxwell Montes range, which rises almost Including the Maxwell Montes range, which rises almost

9 miles9 miles

-Venera orbiter image of a plateau known as Lakshmi Planum

-The Maxwell Montes mountain range (red)

-A meteor crater named Cleopatra is visible on the western slope of the Maxwell range

Ovda RegioOvda Regio A portion of Aphrodite TerraA portion of Aphrodite Terra These cracks in the surface These cracks in the surface

were detected by Magellanwere detected by Magellan The crust appears buckled and The crust appears buckled and

fractured, with ridges running fractured, with ridges running in two distinct directions across in two distinct directions across the image, suggesting that the image, suggesting that large compressive forces are large compressive forces are distorting the crustdistorting the crust

There seem to have been There seem to have been repeated periods when repeated periods when extensive lava flows occurredextensive lava flows occurred

The dark regions are probably The dark regions are probably solidified lava flows solidified lava flows

Volcanism and CrateringVolcanism and Cratering

Many areas of Venus have extensive Many areas of Venus have extensive volcanic features volcanic features

Lava domes probably formed when lava Lava domes probably formed when lava oozed out of the surface, formed the oozed out of the surface, formed the dome, and then withdrew, leaving the dome, and then withdrew, leaving the crust to crack and subside crust to crack and subside

                                                                                        

        

Volcanism and CrateringVolcanism and Cratering Most volcanoes on the planet are Most volcanoes on the planet are

shield volcanoesshield volcanoes They form when lava wells up They form when lava wells up

through a “hot spot” in the crust, and through a “hot spot” in the crust, and are built up over long periods of time are built up over long periods of time by successive eruptions and lava by successive eruptions and lava flows flows

A A calderacaldera,, or crater, forms at the or crater, forms at the summit when the underlying lava summit when the underlying lava withdraws and the surface collapses withdraws and the surface collapses

The distribution of volcanoes over The distribution of volcanoes over the surface of Venus appears the surface of Venus appears random random

Volcanism and CrateringVolcanism and Cratering

The largest volcanic The largest volcanic structures on Venus are structures on Venus are huge, roughly circular huge, roughly circular regions known as regions known as coronae coronae

Roughly circular regions Roughly circular regions thought to have been thought to have been caused by upwelling caused by upwelling mantle material causing the mantle material causing the planet's crust to bulge planet's crust to bulge outward outward

They generally have They generally have volcanoes both in and volcanoes both in and around them around them

                                                                   

          

Current Volcanic Activity?Current Volcanic Activity? There is overwhelming evidence for past surface activity There is overwhelming evidence for past surface activity

on Venuson Venus Two pieces of indirect evidence suggest that volcanism Two pieces of indirect evidence suggest that volcanism

continues todaycontinues today The level of sulfur dioxide above Venus’s clouds shows large The level of sulfur dioxide above Venus’s clouds shows large

and fairly frequent fluctuationsand fairly frequent fluctuations• It is quite possible that these variations result from volcanic It is quite possible that these variations result from volcanic

eruptions on the surfaceeruptions on the surface• If so, volcanism may be the primary cause of Venus’s thick cloud If so, volcanism may be the primary cause of Venus’s thick cloud

covercover Both theBoth the Pioneer Venus Pioneer Venus and the and the VeneraVenera orbiters observed bursts orbiters observed bursts

of radio energy from Aphrodite and other regions of the planet’s of radio energy from Aphrodite and other regions of the planet’s surfacesurface

• These bursts are similar to those produced by lightning discharges These bursts are similar to those produced by lightning discharges that often occur in the plumes of erupting volcanoes on Earth, again that often occur in the plumes of erupting volcanoes on Earth, again suggesting ongoing activity suggesting ongoing activity

AtmosphereAtmosphere The atmosphere of Venus is The atmosphere of Venus is

about 90 times more massive about 90 times more massive than Earth’s, and it extends to than Earth’s, and it extends to a much greater height above a much greater height above the surface the surface

The surface temperature and The surface temperature and pressure of Venus’s pressure of Venus’s atmosphere are much greater atmosphere are much greater than Earth’sthan Earth’s

However, the temperature However, the temperature drops more rapidly with drops more rapidly with altitude, and the upper altitude, and the upper atmosphere of Venus is atmosphere of Venus is actually colder than our own actually colder than our own

AtmosphereAtmosphere

Carbon dioxide-96.5%Carbon dioxide-96.5% Nitrogen-3.5%Nitrogen-3.5% Water vapor, carbon monoxide, sulfur Water vapor, carbon monoxide, sulfur

dioxide, argon-trace amountsdioxide, argon-trace amounts The clouds are composed of sulfuric acidThe clouds are composed of sulfuric acid

Greenhouse EffectGreenhouse Effect The average surface temperature is around 850The average surface temperature is around 850ooF-hot F-hot

enough to melt leadenough to melt lead Venus is very hot because of the greenhouse effectVenus is very hot because of the greenhouse effect The thick carbon dioxide blanket absorbs nearly 99 The thick carbon dioxide blanket absorbs nearly 99

percent of all the infrared radiation released from the percent of all the infrared radiation released from the surface of Venus, and it is the immediate cause of the surface of Venus, and it is the immediate cause of the planet’s sweltering 730 K surface temperature planet’s sweltering 730 K surface temperature

Because Venus’s atmosphere is much thicker and Because Venus’s atmosphere is much thicker and denser than Earth’s, a much smaller fraction of the denser than Earth’s, a much smaller fraction of the infrared radiation leaving the planet’s surface actually infrared radiation leaving the planet’s surface actually escapes into spaceescapes into space

The result is a much stronger greenhouse effect than on The result is a much stronger greenhouse effect than on Earth and a correspondingly hotter planet Earth and a correspondingly hotter planet

Greenhouse EffectGreenhouse Effect

             

                                                                     

Magnetic FieldMagnetic Field

In 1962, In 1962, Mariner 2 Mariner 2 flew by Venus, carrying flew by Venus, carrying magnetometers to measure the strength of the magnetometers to measure the strength of the planet’s magnetic fieldplanet’s magnetic field

None was detected, and subsequent Soviet and None was detected, and subsequent Soviet and U.S. missions, carrying more sensitive detectors, U.S. missions, carrying more sensitive detectors, have confirmed this finding have confirmed this finding

The lack of any detectable magnetic field on The lack of any detectable magnetic field on Venus is almost surely the result of the planet’s Venus is almost surely the result of the planet’s extremely slow rotation extremely slow rotation

ExplorationExploration

In all, some 20 spacecraft have visited Venus since the In all, some 20 spacecraft have visited Venus since the 1970s, far more than have spied on any other planet in 1970s, far more than have spied on any other planet in the solar system the solar system

The American The American Mariner 2Mariner 2 and and Mariner 5Mariner 5 missions passed missions passed within 35,000 km of the planet in 1962 and 1967, and within 35,000 km of the planet in 1962 and 1967, and Mariner 10Mariner 10 grazed Venus at a distance of 6000 km en grazed Venus at a distance of 6000 km en route to its rendevous with Mercury route to its rendevous with Mercury

The Soviet The Soviet VeneraVenera (derived from the Russian word for (derived from the Russian word for Venus) program got under way, and the Soviet Venus) program got under way, and the Soviet Venera 4Venera 4 through through Venera 12Venera 12 probes parachuted into the planet’s probes parachuted into the planet’s atmosphere between 1967 and 1978 atmosphere between 1967 and 1978

VeneraVenera

The early The early VeneraVenera probes were destroyed by enormous probes were destroyed by enormous atmospheric pressures before reaching the surface atmospheric pressures before reaching the surface

in 1970, in 1970, Venera 7Venera 7 became the first spacecraft to soft-land became the first spacecraft to soft-land on the planeton the planet

During the 23 minutes it survived on the surface, it radioed back During the 23 minutes it survived on the surface, it radioed back information on atmospheric pressure and temperature information on atmospheric pressure and temperature

A number of A number of VeneraVenera landers have transmitted landers have transmitted photographs of the surface back to Earth and have photographs of the surface back to Earth and have analyzed the atmosphere and the soilanalyzed the atmosphere and the soil

None of them survived for more than an hour in the planet’s hot, None of them survived for more than an hour in the planet’s hot, dense atmospheredense atmosphere

The data they sent back make up the entirety of our direct The data they sent back make up the entirety of our direct knowledge of Venus’s surface knowledge of Venus’s surface

Pioneer VenusPioneer Venus

The U.S. The U.S. Pioneer VenusPioneer Venus mission in 1978 placed mission in 1978 placed an orbiter at an altitude of some 150 km above an orbiter at an altitude of some 150 km above Venus’s surface and dispatched a “multiprobe” Venus’s surface and dispatched a “multiprobe” consisting of five separate instrument packages consisting of five separate instrument packages into the planet’s atmosphereinto the planet’s atmosphere

During its hour-long descent to the surface, the During its hour-long descent to the surface, the probe returned information on the variation of probe returned information on the variation of density, temperature, and chemical composition density, temperature, and chemical composition with altitude in the atmospherewith altitude in the atmosphere

The orbiter’s radar produced images of most of The orbiter’s radar produced images of most of the planet’s surfacethe planet’s surface

MagellanMagellan

Entered orbit around Venus in Entered orbit around Venus in August 1990 August 1990

Between 1991 and 1994 the Between 1991 and 1994 the probe mapped 98 percent of the probe mapped 98 percent of the surface of Venus with surface of Venus with unprecedented clarity and made unprecedented clarity and made detailed measurements of the detailed measurements of the planet’s gravityplanet’s gravity

The mission ended in October The mission ended in October 1994 with a (planned) plunge into 1994 with a (planned) plunge into the planet’s dense atmosphere, the planet’s dense atmosphere, sending back one final stream of sending back one final stream of high-quality data high-quality data

Venus ExpressVenus Express

It took less than three It took less than three years from the years from the approval to the launch approval to the launch of the mission of the mission

Launched by the Launched by the European Space European Space Agency in 2005Agency in 2005

Arrived at Venus in Arrived at Venus in April of 2006April of 2006

Planet-CPlanet-C Also known as the Venus Also known as the Venus

Climate OrbiterClimate Orbiter A Japanese Space A Japanese Space

Agency (JAXA) mission Agency (JAXA) mission to study the dynamics of to study the dynamics of the atmosphere of Venus the atmosphere of Venus from orbit from orbit

It will also measure It will also measure atmospheric atmospheric temperatures and look for temperatures and look for evidence of volcanic evidence of volcanic activity and lightning activity and lightning

Planned to be launched Planned to be launched in 2010in 2010

Video ClipsVideo Clips

Story of VenusStory of Venus Venus atmosphereVenus atmosphere Venus 1Venus 1 Venus 2Venus 2 Venus 3Venus 3 Visiting VenusVisiting Venus