Astonishing Astronomy 101With Doctor Bones (Don R. Mueller,

Ph.D.)

EducatorEntertainer

JU

G G LE

RPLANETARY

Scientist

ScienceExplorer

Chapter 9 - Venus Earth’s Sister Planet

Venus – Not so twin-like after all.

• Venus, called Earth’s “twin” is only slightly smaller than the Earth, but that’s where the resemblance ends.

• Thick clouds completely obscure the surface.

• It rotates very slowly (once in 243 Earth days), and in the opposite direction to the rest of the planets of the solar system.

• The surface is hot, hot, hot!

The Venusian Atmosphere

• The atmosphere of Venus is quite different from that of Earth:

• 100 times more massive.

• Venus has an atmospheric pressure of about 90 times that of Earth:

Choked by 96.5% carbon dioxide, thick clouds of sulfuric acid and trace amounts of water vapor.

• The planet likely underwent a runaway greenhouse effect.

Images from Venus

• The Russian Venera spacecraft have visited the surface of Venus.

• Surface temperatures: 750 K hot enough to melt lead.

• Discovered volcanic rocks.

• The spacecraft only lasted about an hour due to the extreme temperatures and pressure.

• More recent spacecraft have mapped the surface of Venus from orbit.

The Surface of Venus

• Venus has both highlands and lowlands.

• Surface features: named for prominent women in history and mythology.

• Venus is less mountainous than Earth, with more rolling plains.

• Volcanic peaks are present in the highlands.

Radar map of Venus

• The surface of Venus appears to be relatively young.

• Plenty of volcanic activity resurfaces the planet rapidly.

• With few impact craters, due both to the thick atmosphere and volcanic activity.

Interesting features of the surface of Venus

The Orbit and Rotation of Venus

Venus completes an orbit of the Sun every ~ 225 days.

Of the planets, Venus spins about its axis the slowest:

About 243 Earth days to complete one rotation.

The slow rotation creates almost no magnetic field.

Daily Rotation

The Role of Sunlight

• A planet’s distance from the Sun determines how much sunlight it receives.

• Venus receives ¼ of the energy per square meter that Mercury does.

• Planets in eccentric orbits receive varying amounts of sunlight.

• The axial tilt of a planet determines its seasons.

• Sunlight warms and the atmosphere has an impact too:

• Venus’s atmosphere warms the surface to 750 K, but it would be very warm even without the CO2.

• Mercury is closer to the Sun, but still cooler than Venus.

• The Moon is cooler than the Earth, even though they are at the same distance from the Sun.

• Sunlight also determines the makeup of the planets:– Inner planets are rock and iron

bodies.– Outer planets are gaseous.

Chapter 10 - Mars The Red Planet

Mars

• Mars is the most explored planet (aside from Earth) in the Solar System.

• Mariner 4 provided the first close-up image (1965).

• ESA’s Mars Express (2003).• Global Surveyor• Odyssey• Mars Reconnaissance

Orbiter • And more to follow:

Major Features of Mars

Mars: The home to amazing sites:

• Valles Marineris

(1) Named for Mariner 4(2) A canyon that stretches across

the face of the globe.(3) As wide as the United States.

• Olympus Mons(1) Tallest mountain in the solar

system (26 km tall.)(2) Probably no older than 250

million years.

Map of Mars

• The Tharsis bulge may have been caused by an upwelling of hot material from the interior of the planet, creating volcanoes in the region (including Olympus Mons) and perhaps also Valles Marineris.

Olympus Mons

• Tallest mountain in the Solar System.

• Extends above the bulk of the atmosphere of Mars.

• A volcano around 250 million years old.

• The largest known volcano in the solar system is located on Mars.

Dune Fields

• Deserts ring Mars at its mid-latitudes.

• Winds blow surface material into dunes, similar to those found on Earth.

Ice Caps of Mars

• The polar ice caps of Mars are composed mostly of water ice covered by a relatively thin layer of carbon dioxide.

• Growing and shrinking seasonally.

• Mars has an axial tilt similar to that of Earth: produces seasons similar to those found on Earth.

• Southern winters are more extreme than the north, as Mars is farthest from the sun during this period.

Please insert figure 40.6 A

Water on Mars? Probably flowed freely long ago.

• Many scientists think that Mars was once warmer and wetter than it is today.

• Surface features support this:– Dry riverbeds.– Splash craters (craters that

form from impacts on damp soil).

– Gullies in crater walls.

• Mars must have had a warmer and denser atmosphere in the past to support liquid water on its surface.

Evidence for Water?

Splash Craters

Gullies

Where’s the water? Where did the water go?

• Some water may be trapped just below the surface as permafrost.

• Water may be locked in mineral compounds.

• Most water probably escaped to space:

(1) Evaporated

(2) Dissociated by photons.

The Surface of Mars

• A dry, dusty place.• Covered with rocks

ranging from pebbles to boulders.

• Evidence for flowing water, rivers and salty oceans.

The Martian Atmosphere

• The Martian atmosphere is very different from Earth’s.

95% CO2 and 3% N2

Surface pressure is very low.

Clouds of water ice and carbon dioxide ice float through the sky.

No rainfall, but it sometimes snows dry ice crystals.

Temperatures range from above freezing to 180 K.

• Martian winds, though gentle, can carry dust far into the atmosphere.– These dust storms sometimes

obscure much of the surface.• No erosion.

The Moons of Mars: Phobos and Deimos

Mars has two moons: Phobos and Deimos.Both are small (20 km across): likely captured asteroids.

Chapter 11 - Jupiter The Gas Giant

Jupiter

Jupiter

5 AU from the Sun.

11 times the Earth’s diameter.

300 times the Earth’s mass.

Earth

Jupiter’sAppearance

• Parallel bands of clouds: Dark belts and Light zones.

• Its atmosphere is 90% H2 and 10% He, with traces of methane, ammonia and water.

• The outer atmosphere has a temperature of 160 K.

• Rotates once every 9.9 hours.• Visibly flattened.

Belts Zones

Great Red Spot

The Interior of a Gas Giant

Please insert figure 43.3

The Interior of Jupiter

• Jupiter’s average density is 1.3 kg/liter.

• Jupiter is in hydrostatic equilibrium:Gravity pulls inward and the interior pressure pushes out.The two forces are balanced.

• No solid or liquid surface:The pressure is high enough to create liquid metallic

hydrogen, a fluid that acts like a metal.Jupiter probably has a molten rocky core: larger than the

Earth itself.

• Jupiter generates more heat than it receives from the Sun.

Equatorial Bulge• Jovian planets rotate

much faster than terrestrial planets.

• From the principle of conservation of angular momentum.

• Faster rotational speeds make the outer planets much wider at the equator. The so-called equatorial bulge.

Earth Jupiter

Jupiter’s rapid rotation creates strong Coriolis forces and high winds.

Jupiter’sHigh Winds

Equator

The Great Red Spot

• On Jupiter, these wind shears give rise to enormous vortices or storms, seen as white, brown or red ovals in its clouds.

• The Great Red Spot is one such vortex:

• The longest lasting storm in the solar system.

• The Great Red Spot is a storm that has lasted for at least 300 years!

Magnetic Fields• The liquid metallic

hydrogen in Jupiter can carry electrical currents, similar to the liquid core of the Earth.

• These currents generate very large magnetic fields.

Jupiter’s magnetic field is 20,000 times as strong as Earth’s.

Jupiter experiences auroras.

The Galilean Satellites

• The four largest moons of Jupiter are called the Galilean satellites, in honor of their discoverer, Galileo.

• They appear as pinpoints of light through small telescopes or binoculars.

• An excellent target for amateur astronomers.

The Galilean Satellites

• The Galilean satellites would be considered planets if they orbited the Sun independent of Jupiter.

• Temperatures range from 110-130 K.

Io

Europa

The Galilean Satellites

Callisto

Ganymede

Io is one of the most exotic places in the solar system

• Io is closest to Jupiter and has a very active interior.

• Looks like a giant spherical pizza covered with melted cheese and splotches of tomato and ripe olives. Io is the most volcanically active body in the Solar System.

• The third largest of Jupiter's moons.

• Tidal forces cause Io's surface to bulge in and out by as much as 100 meters (330 feet).

Europa is covered with cracks: Reddish mineral-rich water seeps out to make these cracks visible.

Tidal forces stretch Europa, leading to tidal heating, which in turn melts the surface ice resulting in liquid water.

Metallic Core Ice Cover

LiquidOcean

Water Layer

RockyInterior

Ganymede and Callisto Ganymede• Metal core, covered by a

rocky layer and a 800 km deep ocean.

• Surface is mostly ice, pockmarked by craters.

• Younger grooved terrain from tectonic activity.

Callisto• Less differentiated

than other moons.• Mix of ice and rock in

its interior.• Thin icy crust.