Planet order from Sun Orbital period Semi-major axis Mass Radius Density Surface Gravity Escape speed Rotational Period Inclination ..(axis tilt) Surface Magnetic Field Surface Temperature Number of Moons

Venus 2 0.62 years (225 Earth days) 0.72 AU 0.82 x Earth 0.95 x Earth 5240 kg/m3 0.91 x Earth 10.4 km/s -243 days 177.4° less than 0.001 x Earth (none detected) 730 K 0

Mars 4 1.88 years (687 days) 1.52 AU 0.11 x Earth 0.53 x Earth 3930 kg/m3 0.38 x Earth 5.0 km/s 1.026 days 23.98° 1/800 x Earth about 150-310 K 2

Jupiter 5 11.9 years 5.2 AU 318 x Earth (0.1% of S.S.) 11.2 x Earth 1300 kg/m3 2.5 x Earth 59.5 km/s 0.41 days 3° 14 x Earth 125 K 63 and counting

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Venus

Earth's Sister Planet

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lecture on Venus

Observing Venus from Earth

• Venus never separates from the Sun by more than 47^o, as viewed from the Earth
  • appears above the horizon
    • before sunrise and after sunset.
• Extremely bright
  • (10 x brightest star) (reflectivity = 70%)
  • 3rd brightest object in the sky, next to the Sun and the Moon

Venus - General Properties

• 2nd Planet from the Sun
• semi-major axis ("radius") = 0.72 AU
  • period = 225 days
• Radius = 6052 km = 0.95 R_Earth
• Mass = 4.9 x 10²⁴ kg = 0.82 M_Earth
• Density = 5240 kg/m³
  • Radius, mass, & density are Earth-like or "sister planet"
• Rotational Period = 243 days ( retrograde)
  • Solar day on Venus = 117 Earth days
  • Why retrograde -> collision?
• Atmosphere
  • very dense => high altitude clouds of sulfuric acid block surface
• 90x as massive as the Earth's atmosphere
  • 96.5% CO₂ (by volume)
  • few % Nitrogen (very little water)
• surface temperature = 730K (T_Earth=300K, T_Mercury=100-700K)
• Greenhouse Effect
  • temperature uniformity - poles, equator, day, night

Exploration of Venus

More than 20 spacecraft have visited, more than any other planet
• visits began in the early 1960's
• first soft landing on surface by Soviet Venera 7 in 1970
• Magellan - August 1990
  • produced spectacularly detailed surface images
  • resolution of about 120 m

Venus' atmosphere is different from Earth's?

• On Earth, CO₂ is absorbed in the oceans and rocks.

Summary of Atmospheric Components

(percentages by volume)

CO2 Nitrogen Water Oxygen

Earth absorbed in rock free in atmosphere (78%) mostly condensed on surface product of life (21%)

Venus free in atmosphere (96.5%) free in atmosphere (3.5%) decomposed long ago, and hydrogen escaped no life to produce it

Evolution of Venus' Atmosphere

• During secondary atmosphere formation temperature of Venus high
  • no oceans form (Water is broken down and H escapes) and gases are not absorbed
  • gases in atmosphere trap heat (greenhouse effect)
  • temperature rises even more
  • runaway greenhouse effect

Venus' Surface

• A couple of continental sized features
  • Ishtar Terra (southern high latitudes)
  • Aphrodite Terra (near the equator),
  • with Earth-like mountains
• No oceans
  • rolling plains (65%)
  • lowlands (27%)
  • modest highlands (8%) (continents)
• No plate tectonic activity
• Lava flows -> volcanic origin
• Craters - mostly of volcanic origin
• The surface of Venus is rather young (less than 1 billion years) due to volcanic activity

Volcanism today?

Venus' Magnetic Field and Internal Structure

• Magnetic field - none detectable
  • this is consistent with slow rotation period of 243 days
• Model of internal structure is based on little hard data
  • Surface resembles surface of young Earth (at an age of about 1 billion years)
    • thin crust, volcanic activity,
    • internal convective processes not yet established
    • not yet developed plate tectonics
  • Why no development of plates?
    • Cooling slowly due to high surface temperature
      • crust remains too soft for Earth-style plates to develop
    • absence of water may also be important
      • no lubricating mechanism

Mars

A Near Miss for Life?

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lecture on Mars

General Properties of Mars

• Mars is the 4th Planet from the Sun
  
• semi-major axis ("radius") = 1.52 AU
• closest opposition roughly every 15 years (in August/September) -> brightest
• orbital period = 687 days (1.88 years)
• Radius = 0.53 R_earth
• Mass = 0.11 M_earth
• => Density = 3900 kg/m³
• Rotational Period = 24.6 hours
• Inclination of 24.0° (23.5° for Earth)
  • tilt causes seasons

History of Observations from Earth

• 1877 - Mars is unusually close to Earth
  • Italy: Giovanni Schiaparelli
    • Observed network of linear markings (canali)
  • Percival Lowell, in US
    • Motivated by report of "canals", gives up successful Boston business to build observatory in Flagstaff, Arizona
    • devoted life to studying "canals" and Martian intelligent society

Space Probes to Mars

• Mariner 4 (1965)
  • First spacecraft to reach Mars
• Viking 1 and Viking 2 (1976)
  • landed on Mars and conducted biological experiments to search for evidence of life
• Pathfinder (& Sojouner, landed July 4, 1997)
  • landed at mouth of outflow channel
  • rocks deposited by flood water
• Mars Global Surveyer
  • launched November, 1996
  • start mapping, March, 1999
• Mars Exploration Rover Mission
  • Spirit landed on January 3, 2004, in a rocky landscape
  • Opportunity landed halfway around Mars from Spirit
  • found rocks that had been very wet in the past, after landing on January 23, 2004.
  • The rovers were expected to last 3-6 months, but each continued to explore over a few kilometers and send data back for several years.
    • Spirit stopped communicating in 2010 after traveling over 7 kilometers
    • Opportunity goes on, having traveled over 27 kilometers
• Phoenix Mission
  • landed in North polar region in 2008
  • dug trenches and discovered white material that is almost surely ice
• Major results of these missions
  1. the surface of Mars contains much more iron that the surface of the Earth
     • less differentiation on Mars
  2. so far, no evidence of life, now or in the past

Mars' Atmosphere

• Mars has a very thin atmosphere
  • (1/150 of Earth's atmosphere)
  • 95.3% CO₂ (by volume)
  • surface temperature:
    • noon, summertime 300K
    • night-time - 200K (much colder than on Earth)
      • (T_earth=300K)
• => dust storms (occasionally months-long)
• Composition of Mars' atmosphere similar to Venus, yet 10,000 times thinner
  • -> reverse greenhouse effect

Mars' Surface

• Huge shield volcanoes:
  • Olympus Mons
    • About 700 kilometers in diameter
      • would cover all of Washington and half of Oregon
    • Rises 25 kilometers above the surrounding plains
      • (82,000 feet)
    • (largest volcano in the Solar System)
  • Mariner Valley
    • crack in the surface of the planet
    • huge canyon running along the equator for about 4000 km -about 1/5 the circumference
• Vast dune fields:
• North-south asymmetry:
  • Northern Hemisphere: lava plains -> younger surface
  • Southern Hemisphere: heavily cratered highlands -> older surface
• THE MAJOR FEATURE:
  • Tharsis bulge
    • size of North America, near equator
    • rises 10 km above rest of surface
• Impact cratering:
  • wide spread cratering,
  • eroded by the atmosphere
  • appearance of craters (liquid splash) suggest permafrost (water ice) just below the surface
    • compare this to typical craters on the Moon, such as Copernicus, shown here on the left
• Running water in the past:
  • the best evidence that water once existed in great quantities on the surface is the channels
    • runnoff channels:
      • southern highlands
      • 4 billions years ago
      • - thick atmosphere & surface water
    • outflow channels:(another view)
      • near equator
      • from south to north
      • enormous flow rates> 100xAmazon
      • about 3 billion years ago
  • No water today on the surface
    • a large amount of this water may now be locked in the polar caps and under the surface (permafrost)
• Polar Caps
  • north and south
  • primarily dry ice (CO₂)
  • seasonal variation
  • temperature remains below 150K

Mars' Magnetic Field and Internal Structure

• Mars' has a weak magnetic field
  • => about 1/800 of Earth
  • (but rotation period is similar to Earth 24.6 hours)
    • so -> core is non-magnetic, or has no liquid, or both
• planet probably never differentiated much
  • - large abundance of surface iron

Moons of Mars

• Two very small moons:
  • Phobos (fear) & Deimos (panic)
    • Irregularly shaped and cratered
    • Orbits at about 3 and 7 planetary radii
      • (Earth's Moon orbits at about 60 radii)
    • Both orbit synchronously
      • tidally locked, like the Moon
    • Both orbit prograde direction
    • Large (Stickney) Crater on Phobos
• Captured asteroids?
  • low density like typical asteroid

Martian Asteroids and the Evidence for Life on Mars

• About a dozen meteorites from the surface of Mars have been found on Earth
  • (identified by gases trapped in rocks)
• 1984 - scientists discovered a rock ( ALH84001) on Antarctic ice field
• 1992 - detailed study of the rock - found (within a small region of the rock)
  1. organic molecules that might be associated with life
  2. several minerals characteristic of biological activity
  3. tiny tubular and egg-shaped structures resembling ancient single-celled bacteria found on Earth
• These observations were announced August 7, 1996
• This evidence cannot be established as due to life forms
  • The features could all have been produced by chemical reactions without any involvement of life
  • Could ALH84001 have been contaminated? (it sat on ice in Antarctica for 13,000 years)
  • More evidence is need to resolve this
• NASA plans future visits to Mars to attempt to understand whether life did or did not exist on Mars in the past

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lecture on Jupiter

• Discovery of Jupiter
• Space Probes to Jupiter
• Atmosphere of Jupiter
• Rings of Jupiter
• Internal Structure and Magnetosphere of Jupiter
• Moons of Jupiter

• Jupiter is the third brightest object in the night sky (after the Moon and Venus)
  
  
• Differential rotation
  • period of rotation at equator shorter than at higher latitudes
• Equatorial bulge
  • due to rapid rotation
• Prominent visual features
  • Bands: belts and zones
  • Great Red Spot
  • four prominent moons
    • Discovered by Galileo in 1609
• It takes over half an hour for light (or radio signals from a spacecraft) to get from Jupiter to the Earth
• Jupiter as a "failed star"
  • If Jupiter's mass were 80 times larger, the gravitational collapse would have ignited its hydrogen into thermonuclear fusion, creating a second star in the Solar System

• Jupiter has been known of since ancient time since it is bright in the night sky

• Pioneer 10 - (launched by USA, March 3, 1972)
  • flew by Jupiter on December 1, 1973
  • Carrying a gold, anodized plaque intended to communicate with extraterrestrials
• Pioneer 11 - (launched by USA, April 6, 1973)
  • flew by Jupiter on December 1, 1974
  • flew by Saturn in 1979
• Voyager 1 - (launched by USA, September 5, 1977)
  • Voyager 1 flew by Jupiter on March 5, 1979
  • flew by Saturn on Nov 13, 1980
• Voyager 2 - (launched by USA, August 20, 1977)
  Voyager 2 flew by Jupiter on July 9, 1979
  • flew by Saturn on Aug 27, 1981
  • flew by Uranus on Jan 30, 1986
  • flew by Neptune on Aug 15, 1989
• Galileo - (launched by USA and Europe, October 18, 1989)
  Galileo was designed to study Jupiter's atmosphere, satellites and surrounding magnetosphere for 2 years.
  • During the journey, Galileo made encounters with asteroids
    • Gaspra on October 29, 1991
    • Ida and moon Dactyl on August 28, 1993.
  • During voyage, had direct view of the Comet Shoemaker-Levy impacts on Jupiter (July, 1994)
  • Arrived at Jupiter, December, 1995
  • Significantly advanced our knowledge of the Galilean moons

Elemental Makeup of Jupiter's Atmosphere
• 86.1% molecular hydrogen (by number)
  
• 13.8% helium (by number)
  
• traces of methane (CH₄), ammonia (NH₃), and water vapor (H₂O)
• little of the early atmosphere escaped due to the strong gravity (large escape velocity)
  
Clouds: Bands and Spots caused by different chemistry vs. altitude
Zones and belts appear as we see different depths of the atmosphere
• Zones(light warm, rising regions)
• Belts (dark ; cool, falling regions)
Zonal Flow

Great Red Spot
• Large hurricane in the south
  • about 2 times the size of Earth
  • at least 300 years old
• revolves with inner region of Jupiter
• rotates counterclockwise
Other storm related features
• gigantic lightning flashes and Auroral activity
• White ovals and Brown ovals
  • persist for many years or decades

• Faint ring discovered by Voyager I
  Main ring lies above cloud layer and inside orbit of innermost moon
• Galileo spacecraft has explored the ring, and concluded that the ring system ( main ring + gossamer rings) has been formed by the dust kicked up when interplanetary meteoroids smash into the inner moons
  

Jupiter's Internal Structure

Emits twice as much energy as it receives from the Sun
• ---> internal heat built up during Jupiter's formation is slowly leaking out
  • gravitational energy
Atmosphere gets denser and denser towards its interior
• gaseous hydrogen
• liquid hydrogen
• liquid metallic hydrogen (generates large magnetic field)
• rocky core (about 5 times Earth's mass)