ISP 205 - Astronomy Gary D. Westfall1Lecture 11 The Planet Venus The Moon and Mercury are geologically dead Venus, Earth, and Mars are still active geologically

1ISP 205 - Astronomy Gary D. Westfall Lecture 11

The Planet VenusThe Planet Venus• The Moon and Mercury are geologically dead

• Venus, Earth, and Mars are still active geologically

• Venus is the planet nearest to Earth, sometimes approaching to within 40 million km

• The orbit of Venus is nearly circular at a distance of 108 million km (0.72 AU)

• Venus is very bright in the sky

“Evening star” “Morning star”


Appearance of VenusAppearance of Venus

• Venus looks very bright to the naked eye and even a small telescope shows that Venus goes through phases like the Moon

• The surface of Venus is always obscured by a very dense cloud cover

Reflects 70% of the sunlight

• Various bands are visible in different wavelength light

Enhanced picture of Venus shot through a violet filter by the Galileo spacecraft


Phases of VenusPhases of Venus• Venus appears to go through phases• Different from Moon because distance changes drastically


Current Position of Venus and MarsCurrent Position of Venus and Mars• Current position of inner planets, Oct. 4


Basic Properties of VenusBasic Properties of Venus• Venus is the second planet from the Sun• Venus is nearly the same size as Earth

12,102 km in diameter(12,756 km for Earth) 82% the mass of Earth Similar density, 5.3 g/cm3 (5.5 g/cm3 for Earth)

• Venus takes 223 days to orbit the Sun

• Venus takes 2,243days to rotate on it axis and it rotates the opposite direction of Earth QuickTime™ and a

decompressorare needed to see this picture.

QuickTime™ and a decompressor

are needed to see this picture.


The Atmosphere of VenusThe Atmosphere of Venus• The atmosphere of Venus causes a very high surface

temperature and gives the surface a perpetual red twilight• The weather at the surface is hot, dry, calm• The pressure at the surface is 90 times the Earth’s

atmospheric pressure

Gas %Carbon

Dioxide (CO2)95.3

Nitrogen (N2) 2.7

Argon (Ar) 1.6

Oxygen (O2) 0.15

Neon (Ne) 0.0003


Surface Temperature of VenusSurface Temperature of Venus• The surface temperature of Venus is 700 K

800 degrees Fahrenheit

• Caused by the greenhouse effect Venus has 1 million times more CO2 than Earth

• Sunlight that diffuses through the atmosphere heats the surface and the CO2 acts as a blanket The surface heats up until the radiation of heat is the

same as the absorption of heat from the Sun

• The dense atmosphere makes the temperature the same everywhere on the surface of Venus Little weather


Implications for EarthImplications for Earth• The atmosphere is the result of a runaway

greenhouse effect Not just a larger greenhouse effect like the increase in

CO2 in the Earth’s atmosphere Irreversible

• If Venus had oceans like Earth, they would have been evaporated into water vapor Water vapor is also a greenhouse gas Once in the atmosphere, UV from the Sun can break

up the water vapor into the constituent hydrogen and oxygen

Hydrogen can then escape Water is permanently gone


Probing Through the CloudsProbing Through the Clouds• Venus has been visited by several spacecraft

• The first spacecraft to land on the surface was

• Shown below is an image taken by the Russian spacecraft Venera 13 on the surface of Venus Venera 13 landed on the surface of Venus on March 1,

1982, survived 2 hours and 7 minutes and sent back 14 pictures


The Magellan Mission to VenusThe Magellan Mission to Venus• The Magellan mission to Venus was launched May 4,

1989 and arrived at Venus on August 10, 1990• Magellan used a high resolution radar to map the surface

of Venus through the opaque clouds• Magellan worked for 4 years and mapped 98% of the

surface of Venus


Mapping the Surface of VenusMapping the Surface of Venus• The Magellan data can be processed into 3-D

views of the surface of Venus

False color picture of Venus constructed from radar images from the Magellan space craft

3-D view of three impact crater on the surface of Venus


Craters on the Surface of VenusCraters on the Surface of Venus• Dating the surface of a planet is

not the same as dating the entire planet

• The largest crater on Venus is the Mead Crater

The Mead Crater - 280 km in diameter

Larger than the largest crater on Earth

• The thick atmosphere of Venus does not protect the surface from impacts

Small projectiles burn up Large projectile make it to the surface There are few craters smaller than 10 km in diameter

• We can use craters with diameters greater the 30 km


Implications for the Age of the SurfaceImplications for the Age of the Surface• There are only about 15% as many craters on the

plains of Venus as on the maria of the Moon Gives an age of about 500 million years

• Indicates Venus has an active geological history

• All the craters look fresh No evidence of erosion be volcanic activity or wind

• Little has happened since the plains of Venus were resurfaced by large scale volcanic activity

• Apparently Venus experienced a volcanic calamity 500 million years ago


Volcanoes on VenusVolcanoes on Venus• Venus is a planet with wide-scale volcanics activity• In the lowland plains, lava renews the surface and erases

craters• The are many volcanoes associated with surface hot spots

• The largest volcano on Venus is Sif Mons

3 km high, 500 km across Caldera is 40 km across

• These volcanoes result from magma reaching the surface

• Pressure under the surface can cause bulges called coronae Computer generated 3-D view of Sif Mons using data

from Magellan


The Planet MarsThe Planet Mars• Mars is the third planet from the Sun

• Mars is the seventh largest planet

• Mars orbits the Sun in 687 days (1.88 years)

• Mars has an eccentric orbit (e = 0.09) with a semimajor axis of 230 million km (1.52 AU)

• Mars rotates on its axis every 24.6 hours

• Mars’ axis is tilted 25.2 degrees


Appearance of MarsAppearance of Mars• To the naked eye, Mars appears to be a small, reddish star• With a telescope, one can make out features on the

surface of Mars With the best Earth-bound telescopes, we can make out features

on the order of 100 km, similar to the Moon with the naked eye No topographical features visible

In 1877, the Italian astronomer Sciaperelli announced he saw lines on Mars that he called canale which were mistakenly translated as canals

This observation combined with the observation of the polar ice caps, led to the idea that intelligent life existed on Mars


Lowell’s CanalsLowell’s Canals• The American astronomer Lowell built an

observatory in Flagstaff, Arizona and concentrated on studying Mars

• Lowell claimed he saw canals on Mars and that these canals were evidence of intelligent life on Mars

• Most other observers could not see the canals

• The idea of canals on Mars lasted into the 1930s

• Sparked the idea of “Men from Mars”


Spacecraft Exploration of MarsSpacecraft Exploration of Mars• The first visitor to Mars was Mariner 4

in 1965 Showed a bleak planet with abundant

craters, no canals

• Mariner 9 became the first spacecraft to orbit another planet in 1971

Showed volcanoes, canyons, layered polar caps, and channels that appeared to have been cut by running water

Photo taken by Mariner 4 showing first unambiguous evidence for craters on Mars

Photo of the caldera of Olympus

Mons taken by Mariner 9

• In 1976 two Viking landers were sent to Mars

• In 1997 less expensive missions were begun


Global PropertiesGlobal Properties• The diameter of Mars is 6790 km, just over half

the diameter of Earth• The density of Mars is 3.9 g/cm3, suggesting that

Mars has a small metallic core• Mars has no magnetic field• About half the surface consists of older, higher

elevation highlands that are highly cratered, mainly in the southern hemisphere

• The remaining half, mainly in the northern hemisphere, consists of young lightly cratered volcanic plains about 4 km lower than the highlands


Main Surface FeaturesMain Surface Features• There are four prominent surface features on Mars

Olympus Mons: the largest mountain in the Solar System rising 24 km (78,000 ft.) above the surrounding plain. Its base is more than 500 km in diameter and is rimmed by a cliff 6 km (20,000 ft) high.

Tharsis: a huge bulge on the Martian surface that is about 4000 km across and 10 km high.

QuickTime™ and aSorenson Video decompressorare needed to see this picture.

Valles Marineris: a system of canyons 4000 km long and from 2 to 7 km deep (top of page);

Hellas Planitia: an impact crater in the southern hemisphere over 6 km deep and 2000 km in diameter.


Olympus Mons and Tharsis Olympus Mons and Tharsis • This movie shows an

animation of the Olympus Mons caldera

The opening is 65 km across


• This picture shows the Tharsis bulge

Contains 12 large volcanoes

Crater history indicates activity ceased 2 billion years ago

QuickTime™ and aPhoto - JPEG decompressor



Mariner Valley and Hellas Planitas Mariner Valley and Hellas Planitas • Mariner Valley is

3000 km long and 8 km deep

• Animation shows a fly-by along the Valley


• The Hellas Impact Basin is 2100 km across and 9 km deep

CO2 frost is visible in upper globe picture

QuickTime™ and aPhoto - JPEG decompressor



View in the Chryse BasinView in the Chryse Basin• Viking 1 and Pathfinder landed in the Chryse Basin which may

have held a shallow sea

Pathfinder picture showing wide angle view of Chryse Planita

Pathfinder picture showing Sojourner

Viking 1 picture

showing angular

rocks and fine dust


View in the Utopia PlanitaView in the Utopia Planita• Viking 2 landed in Utopia Planita

Surface here is rockier and less hilly than Chryse.

Many of the rocks were ejected from nearby

impact crater.

Water-ice frost forms during winter


The Sky on MarsThe Sky on Mars• Pathfinder took pictures of the color of the sky on Mars

Dust particles in the atmosphere give the sky a reddish tint

Noon on Mars

Sunset on Mars


Martian SamplesMartian Samples• Martian meteorites have been found in Antarctica

• May have come from Mars as remnants of a large impact Chemical composition matches Trapped gasses match Martian composition Some structures resemble fossilized life Recent studies do not support those conclusions

Meteorite ALH84001 found in AntarcticaStructures that resemble fossilized life


The Moons of MarsThe Moons of Mars

• Mars has two moons (more later on these moons) Deimos Phobos



Deimos Phobos


Clouds on MarsClouds on Mars• The atmospheric pressure on Mars is less the 1%

that of Earth

• Several type of clouds form in the atmosphere of Mars Dust clouds

Can reach planet-wide proportions Water ice clouds Carbon dioxide clouds

• Because of the low pressure on Mars, water cannot exist as a liquid Ice goes directly from solid to gas

Water ice clouds

Dust storm


Polar Ice CapsPolar Ice Caps• Mars has polar ice caps

Seasonal ice caps are composed of frozen CO2 During winter, these ice caps can extend down to

latitude 50 degrees Permanent ice caps

Southern ice cap composed of CO2 and water Northern ice cap composed of water

Water stays frozen at much higher temperatures than frozen CO2

Huge reservoir of water the size of the Mediterranean Sea

Two caps are different because of the eccentricity of Mars’ orbit around the Sun combined with the tile of Mars’ rotational axis

North polar cap

South polar cap


Water on the Surface of MarsWater on the Surface of Mars• Some evidence shows that flowing water once

existed on the surface of Mars Runoff channels Outflow channels

• Where did the water come from? One idea is that frozen water under the surface melted

and flowed

Outflow network

Documents

ISP 205 - Astronomy Gary D. Westfall1Lecture 11 The Planet Venus The Moon and Mercury are geologically dead Venus, Earth, and Mars are still active geologically