15 February 2005 AST 2010: Chapter 9 1

Venus Venus & &

MarsMars

15 February 2005 AST 2010: Chapter 9 2

Nearest PlanetsNearest PlanetsVenusVenus and and MarsMars resemble Earth resemble Earth more than any other more than any other planetsplanets

But the three are very different But the three are very different from each otherfrom each other

Venus and Mars are among the Venus and Mars are among the brightest objects in the night skybrightest objects in the night sky

Intriguing questions:Intriguing questions:Will we someday be able to visit Venus or Mars?Will we someday be able to visit Venus or Mars?

Does alien life exists on either?Does alien life exists on either?

Can studying these planets give us Can studying these planets give us clues to Earth’s origin, or future?clues to Earth’s origin, or future?

Venus

Mars

15 February 2005 AST 2010: Chapter 9 3

Appearance of VenusAppearance of VenusVenus gets closer to Earth (about 40 million km) Venus gets closer to Earth (about 40 million km) than does any other planetthan does any other planet

Venus sometimes appears as a bright Venus sometimes appears as a bright object near the Sun after sunset (an object near the Sun after sunset (an “evening star”) or before sunrise (a “morning “evening star”) or before sunrise (a “morning star”)star”)

Galileo discovered that Venus Galileo discovered that Venus goes throughgoes through phasesphases, like the Moon, like the Moon

Venus is Venus is shrouded by thick cloudsshrouded by thick clouds, , making it impossible to view its making it impossible to view its surface, even with cameras in orbit surface, even with cameras in orbit around the planetaround the planet

15 February 2005 AST 2010: Chapter 9 4

Appearance of MarsAppearance of MarsAbout every 24 months the Earth and Mars About every 24 months the Earth and Mars are at their closest (~56 million km apart)are at their closest (~56 million km apart)

Mars is reddish due to the presence of iron Mars is reddish due to the presence of iron oxides (rust) in its soiloxides (rust) in its soil

Around 1900, Percival Lowell thought he saw Around 1900, Percival Lowell thought he saw canals on Mars!canals on Mars!

It is now generally accepted that what he saw was It is now generally accepted that what he saw was an an optical illusionoptical illusion

Mars has polar ice caps, Mars has polar ice caps, thin clouds, and dust thin clouds, and dust stormsstorms

Two faces of Mars

15 February 2005 AST 2010: Chapter 9 5

Rotation of Venus and MarsRotation of Venus and MarsThe rotation (spinning) of Mars has been The rotation (spinning) of Mars has been measured by observing features on the planet measured by observing features on the planet over a very long time, about 200 yearsover a very long time, about 200 years

Mars’ Mars’ siderealsidereal rotation period is 24 h 37m 23s, rotation period is 24 h 37m 23s, about 40 minutes longer than Earth’sabout 40 minutes longer than Earth’s

The rotation (spinning) of Venus is measured The rotation (spinning) of Venus is measured using radar, but (unlike Mercury) the radar is using radar, but (unlike Mercury) the radar is used to observe the motion of Venus’ surface used to observe the motion of Venus’ surface featuresfeatures

Venus’ sidereal rotation period is 243 days!Venus’ sidereal rotation period is 243 days!

SurpriseSurprise: Venus spins in a : Venus spins in a backwardbackward or or retrograderetrograde direction!!direction!!

15 February 2005 AST 2010: Chapter 9 6

Properties of Earth, Venus, and MarsProperties of Earth, Venus, and Mars

15 February 2005 AST 2010: Chapter 9 7

Basic PropertiesBasic PropertiesVenusVenus

Similar to Earth in size, Similar to Earth in size, mass, and high mass, and high geological activitygeological activityHas thick atmosphere Has thick atmosphere consisting mostly of consisting mostly of carbon dioxide (COcarbon dioxide (CO22))Atmospheric pressure Atmospheric pressure almost 100 times almost 100 times greater than Earth’sgreater than Earth’sSurface very hot, with Surface very hot, with temperature of 730K temperature of 730K (over 850° F)(over 850° F)

MarsMarsRather small in mass Rather small in mass and size compared to and size compared to EarthEarthMay have had May have had significant geological significant geological activity in the pastactivity in the pastHas thin atmosphereHas thin atmosphereProbably had thick Probably had thick atmosphere and liquid atmosphere and liquid water in the pastwater in the past

Which could have Which could have supported lifesupported life

15 February 2005 AST 2010: Chapter 9 8

The Geology of VenusThe Geology of VenusVenus being similar size and Venus being similar size and composition to the Earth, we might composition to the Earth, we might expect the two planets to have similar expect the two planets to have similar geologygeology

This is partly true, but Venus does not This is partly true, but Venus does not exhibit the same kind of plate tectonics as exhibit the same kind of plate tectonics as the Earththe Earth

Early missions to Venus:Early missions to Venus:1962: U.S. Mariner 2 did a flyby1962: U.S. Mariner 2 did a flyby1970: Soviet Venera 7 became the first craft to 1970: Soviet Venera 7 became the first craft to land on Venus and broadcast back pictures for 23 land on Venus and broadcast back pictures for 23 minutes (before succumbing to heat)minutes (before succumbing to heat)

15 February 2005 AST 2010: Chapter 9 9

Missions to VenusMissions to Venus

More spacecraft have visited More spacecraft have visited Venus than any other Venus than any other planetplanet

Additional missions to VenusAdditional missions to Venus1970: more Venera probes made photographs as 1970: more Venera probes made photographs as well as analyzed the soil and atmospherewell as analyzed the soil and atmosphere

1970s: U.S. Pioneer Venus orbiter made the first 1970s: U.S. Pioneer Venus orbiter made the first crude global radar mapcrude global radar map

1980s: Soviet Venera 15 and 16 radar orbiters 1980s: Soviet Venera 15 and 16 radar orbiters made better radar mapsmade better radar maps

1991-1993: U.S. Magellan spacecraft made radar 1991-1993: U.S. Magellan spacecraft made radar maps with 100-m resolutionmaps with 100-m resolution

Images taken by Venera 13

15 February 2005 AST 2010: Chapter 9 10

Radar Maps of VenusRadar Maps of Venus

N

S

1

2

15 February 2005 AST 2010: Chapter 9 11

Craters and Surface Age of VenusCraters and Surface Age of VenusCrater counting used to Crater counting used to estimate surface ageestimate surface age

Largest crater, called Meade, Largest crater, called Meade, 275km in diameter275km in diameter

Thick atmosphere seems to Thick atmosphere seems to stop only small projectilesstop only small projectiles

Almost no craters smaller than 10 Almost no craters smaller than 10 km in diameterkm in diameter

Counting of larger craters Counting of larger craters suggests surface age of suggests surface age of roughly 500 million yearsroughly 500 million years

Probable indication of persistent Probable indication of persistent geological activitygeological activity

15 February 2005 AST 2010: Chapter 9 12

Volcanoes on VenusVolcanoes on VenusSignificant volcanismSignificant volcanismLargest volcano, called Largest volcano, called Sif Mons, wider but lower Sif Mons, wider but lower than Mauna Loa in Hawaiithan Mauna Loa in HawaiiSome volcanoes have Some volcanoes have shapes like “pancake shapes like “pancake domes”domes”Volcanic bulges called Volcanic bulges called coronaecoronae are common are common

These are produced by These are produced by hot magma from the hot magma from the planet’s interior which planet’s interior which does not make it to the does not make it to the surfacesurface

Computer-generated view of Sif MonsComputer-generated view of Sif Mons

Pancake-dome volcanoesPancake-dome volcanoes

15 February 2005 AST 2010: Chapter 9 13

The Massive Atmosphere of The Massive Atmosphere of VenusVenus

Atmosphere is 96% carbon dioxide, 3.5% Atmosphere is 96% carbon dioxide, 3.5% nitrogen, and very little elsenitrogen, and very little else

The COThe CO22 traps heat on the planet via the traps heat on the planet via the greenhouse effectgreenhouse effect

Surface temperature is Surface temperature is more than 700 K (850°F)more than 700 K (850°F)

15 February 2005 AST 2010: Chapter 9 14

Birth of VenusBirth of Venus

Backward rotation of Venus may have been Backward rotation of Venus may have been caused by a giant impact early in its history caused by a giant impact early in its history

The massive atmosphere and high surface The massive atmosphere and high surface temperature of Venus may have been caused temperature of Venus may have been caused by by runaway greenhouse effectrunaway greenhouse effect

15 February 2005 AST 2010: Chapter 9 15

The Geology of The Geology of MarsMars

Mars is more hospitable Mars is more hospitable than Venus to humans, making than Venus to humans, making Mars more interestingMars more interesting

Early missions to Mars: Early missions to Mars: 1965: Mariner 4 fly by1965: Mariner 4 fly by

1971: Mariner 9 was the first to orbit1971: Mariner 9 was the first to orbit

1976: Vikings 1 and 2 landed1976: Vikings 1 and 2 landed

20 years passed with 2 failed missions20 years passed with 2 failed missions

15 February 2005 AST 2010: Chapter 9 16

Spacecraft Exploration of Spacecraft Exploration of MarsMars

Recent missions:Recent missions:1997: Pathfinder landed and 1997: Pathfinder landed and Mars Global Surveyor orbitedMars Global Surveyor orbited

2002: Another craft orbited2002: Another craft orbited

2004: 2 U.S., 1 European Space Agency, and 1 2004: 2 U.S., 1 European Space Agency, and 1 Japanese craft sent (Japanese craft failed to orbit Japanese craft sent (Japanese craft failed to orbit and ESA rover, Beagle, didn’t function, but U.S. and ESA rover, Beagle, didn’t function, but U.S. landers succeeded)landers succeeded)

15 February 2005 AST 2010: Chapter 9 17

Global Properties of MarsGlobal Properties of MarsMars’ diameter is half Earth’s Mars’ diameter is half Earth’s

A small metal core, but no magnetic fieldA small metal core, but no magnetic field

We have good maps of Mars’s surface We have good maps of Mars’s surface showing:showing:

Olympus Mons: highest peak in the solar systemOlympus Mons: highest peak in the solar system

Vallis Marineris: largest canyon in the solar systemVallis Marineris: largest canyon in the solar system

Highlands and lowlandsHighlands and lowlandsHighlands believed to be older than Highlands believed to be older than lowlandslowlands

Computer-generated rendering Computer-generated rendering of Olympus Monsof Olympus Mons

15 February 2005 AST 2010: Chapter 9 18

Topographic Map of MarsTopographic Map of Mars

15 February 2005 AST 2010: Chapter 9 19

Volcanoes on MarsVolcanoes on Mars

The lowland plains may The lowland plains may have formed 3 to 4 have formed 3 to 4 billion years agobillion years ago

Lava flowsLava flows

Largest volcanoes on Largest volcanoes on the Tharsis bulgethe Tharsis bulge

3 shown at right3 shown at right

Olympus Mons is largest, Olympus Mons is largest, larger than Mauna Loa in larger than Mauna Loa in HawaiiHawaii

15 February 2005 AST 2010: Chapter 9 20

Martian Cracks and CanyonsMartian Cracks and Canyons

Valles Marineris is the Valles Marineris is the largest canyon in the largest canyon in the solar systemsolar system

Formed by tectonic Formed by tectonic cracking in the Tharsis cracking in the Tharsis bulgebulge

L.A. to N.Y.L.A. to N.Y.

Landslides in valley are Landslides in valley are evidence of erosion evidence of erosion (water?)(water?)

15 February 2005 AST 2010: Chapter 9 21

Martian Polar Caps and ClimateMartian Polar Caps and ClimateThin atmosphere, like Earth’s 30km upThin atmosphere, like Earth’s 30km up

Mostly COMostly CO22

Clouds of dust, HClouds of dust, H22O, and COO, and CO22

Seasonal ice caps of COSeasonal ice caps of CO22 (dry ice) (dry ice)

Permanent polar caps (south) have HPermanent polar caps (south) have H22OO

Ice in the soil (permafrost)Ice in the soil (permafrost)

15 February 2005 AST 2010: Chapter 9 22

Climate Change on MarsClimate Change on MarsMars suffers from Mars suffers from runaway refrigerator effectrunaway refrigerator effect

Mars might have had a much thicker atmosphere Mars might have had a much thicker atmosphere and milder climate in the pastand milder climate in the pastMars has smaller surface gravity than Venus or Mars has smaller surface gravity than Venus or EarthEarthAtmospheric gases can escape into space, cooling Atmospheric gases can escape into space, cooling off the planet (evaporative cooling)off the planet (evaporative cooling)

15 February 2005 AST 2010: Chapter 9 23

Life on MarsLife on Mars

15 February 2005 AST 2010: Chapter 9 24

Search for Life on MarsSearch for Life on MarsLife as we know it needs waterLife as we know it needs water

If Mars had had water in the past, life could If Mars had had water in the past, life could have existed therehave existed there

Scientists have tried looking for signs of life on Scientists have tried looking for signs of life on Mars in a variety of ways, so far with negative Mars in a variety of ways, so far with negative resultsresults

It could be that UV light has sterilized the It could be that UV light has sterilized the surface, but could microbes live below?surface, but could microbes live below?

Some scientists claimed that a meteorite from Some scientists claimed that a meteorite from Mars shows possible evidence of life in its past Mars shows possible evidence of life in its past (see next slide)(see next slide)

15 February 2005 AST 2010: Chapter 9 25

Martian MeteoriteMartian Meteorite