1AST 2010: Chapter 914 July 2005

VenVenusus &&

MarMarss

14 July 2005 AST 2010: Chapter 9 2

Nearest PlanetsNearest PlanetsVenus and Mars resemble Earth more than any other planets

But the three are very different from each other

Venus and Mars are among the brightest objects in the night skyIntriguing questions:

Will we someday be able to visit Venus or Mars?Does alien life exists on either?Can studying these planets give us clues to Earth’s origin, or future?

VenusVenus

MarsMars

14 July 2005 AST 2010: Chapter 9 3

Appearance of VenusAppearance of VenusVenus gets closer to Earth (about 40 million km) than does any other planetVenus sometimes appears as a bright object near the Sun after sunset (an “evening star”) or before sunrise (a “morning star”)Galileo discovered that Venus goes through phases, like the MoonVenus is shrouded by thick clouds, making it impossible to view its surface, even with cameras in orbit around the planet

14 July 2005 AST 2010: Chapter 9 4

Appearance of MarsAppearance of MarsAbout every 24 months the Earth and Mars are at their closest (~56 million km apart)Mars is reddish due to the presence of iron oxides (rust) in its soilAround 1900, Percival Lowell thought he saw canals on Mars!

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

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

Two faces of Mars

14 July 2005 AST 2010: Chapter 9 5

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

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

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

Venus’ sidereal rotation period is 243 days!Surprise: Venus spins in a backward or retrograde direction!!

14 July 2005 AST 2010: Chapter 9 6

Properties of Earth, Venus, and Properties of Earth, Venus, and MarsMars

Terrestrial PlanetsTerrestrial Planets

MercuryMercury VenusVenus EarthEarth MarsMars

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Basic PropertiesBasic PropertiesVenus

is similar to Earth in size, mass, and high geological activityhas a thick atmosphere consisting mostly of carbon dioxide (CO2)has a surface pressure almost 100 times greater than Earth’shas a very hot surface, with temperature of 730 K (over 850° F)

Marsis rather small in mass and size compared to Earthmay have had significant geological activity in the pasthas a thin atmospheremay have had a thick atmosphere and liquid water in the past

which could have supported life

14 July 2005 AST 2010: Chapter 9 9

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

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

To study Venusian geology, we needed to make a global study of its surface

This task is made very difficult by its massive atmosphereThe solution is to use a radar instrument to probe through the thick clouds

More spacecraft have visited Venus than any other planet

14 July 2005 AST 2010: Chapter 9 10

Missions to VenusMissions to VenusMissions to Venus:

1962: U.S. Mariner 2 did a flyby1970: Soviet Venera 7 became the first craft to land on Venus and broadcast back pictures for 23 minutes (before succumbing to the extreme heat)1970s: more Venera probes made photographs as well as analyzed the soil and atmosphere1970s: U.S. Pioneer Venus orbiter made the first crude global radar map1980s: Soviet Venera 15 and 16 radar orbiters made better radar maps1991-1993: U.S. Magellan spacecraft made radar maps from orbit, at a resolution of 100 m

Images taken by Venera 13

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A Radar Map of VenusA Radar Map of VenusAn image of Venus made by the Magellan spacecraftColors have been added to indicate elevation

Blue means low and red high

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Impact Craters and Surface Age Impact Craters and Surface Age of Venusof Venus

Crater counting has been used to estimate the age of Venusian surfaceThe largest crater, called Meade, is 275 km in diameterVenus’s thick atmosphere seems to stop only small projectiles

Very few craters smaller than 10 km in diameter have been found

The counting of larger craters suggests a surface age of roughly 500 million years

This is a probable indication of persistent geological activity

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Volcanoes on Volcanoes on VenusVenus

Significant volcanismLargest volcano, called Sif Mons, wider but lower than Mauna Loa in HawaiiSome volcanoes have shapes like “pancake domes”Volcanic bulges called coronae are common

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

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

Pancake-dome volcanoesPancake-dome volcanoes

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Massive Atmosphere of VenusMassive Atmosphere of VenusThe atmospheric composition is 96% carbon dioxide (CO2), 3.5% nitrogen, and very little elseThe CO2 traps heat on the planet via the greenhouse effectThe surface of Venus has a temperature above 700 K (850°F)

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Birth of VenusBirth of Venus

The backward rotation of Venus may have been caused by a giant impact early in its history The massive atmosphere and high surface temperature of Venus may have been caused by runaway greenhouse effect

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Geology of Geology of MarsMars

Mars is more hospitable than Venus to humans, making Mars more interestingEarly missions to Mars:

1965: Mariner 4 fly by1971: Mariner 9 was the first to orbit1976: Vikings 1 and 2 landed20 years passed with 2 failed missions

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Spacecraft Exploration of MarsSpacecraft Exploration of MarsRecent missions:

1997: Pathfinder landed and Mars Global Surveyor orbited2002: Another craft orbited2004: 2 U.S., 1 European, and 1 Japanese craft sent

European and Japanese craft failed, but U.S. landers (rovers) succeeded

Animation of rovers’ flight to Mars

PathfinderPathfinder

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Global Properties of MarsGlobal Properties of MarsMars’ diameter is half Earth’s It probably has a small metal core, but no magnetic field

Apparently the planet has no liquid material in its core today

The Mars Global Surveyor has produced maps of the entire planet, showing

Highlands and lowlandsThe highlands are thought to be older than lowlands

Olympus Mons, the highest peak in the solar systemVallis Marineris, the largest canyon in the solar system

Computer-generated Computer-generated rendering of Olympus Monsrendering of Olympus Mons

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Topographic Maps of MarsTopographic Maps of Mars

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Volcanoes on MarsVolcanoes on MarsThe lowland plains look similar to the lunar maria

This suggests that the plains may have formed 3 to 4 billion years ago

The largest volcanoes are found on the Tharsis area

3 of them are shown at rightOlympus Mons is the largest, larger than Mauna Loa in Hawaii

14 July 2005 AST 2010: Chapter 9 21

Martian Cracks and CanyonsMartian Cracks and CanyonsValles Marineris is the largest canyon in the solar system

formed by tectonic cracking in the Tharsis bulge

not by running water

It extends for about 5,000 km

similar to the distance from L.A. to N.Y.

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Martian Atmosphere and Martian Atmosphere and Polar CapsPolar Caps

Its atmosphere is thinlike the thin air about 30 km above the Earth’s surfacecomposed mostly of CO2

plus about 3% nitrogen and 2% argon

Various types of clouds can form on MarsDust clouds, raised by windsWater-ice clouds, similar to those on EarthCO2 (dry ice) clouds

Mars has seasonal polar caps made of CO2 (dry ice)Mars also has permanent or residual polar caps

composed of frozen CO2 and water ice in the southmuch larger and composed of water ice in the north

Liquid water on Martian surface is not possible today due to its very low pressure and temperature

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Climate Change on MarsClimate Change on MarsMars might have had a much thicker atmosphere and milder climate in the pastThe cold, dry Mars we see today may have been the result of some sort of runaway refrigerator effect

The surface gravity of Mars is smaller than that of Venus or EarthAtmospheric gases on Mars can escape into space more easily than those on Venus or EarthAs more and more of the gases escaped into space, the surface temperature gradually fell Eventually the planet became so cold that water froze out of the atmosphere, further reducing its ability to retain heat

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Channels & Gullies on MarsChannels & Gullies on MarsGeological features on Mars that appear to be evidence of water erosion in the distant and recent past have been seen:

runoff channelsoutflow channelsgullies

25AST 2010: Chapter 914 July 2005

Is There Life on Mars ?Is There Life on Mars ?

Video evidence

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Search for Life on MarsSearch for Life on MarsLife as we know it needs waterIf Mars had had water in the past, life could have existed thereIt could be that UV light has sterilized the surface, but could microbes live below?Scientists have tried looking for signs of life on Mars in a variety of ways, so far with negative resultsThe search continues …

Mars rovers’ website