Section 10: Earthlike Planets - Venus and Mars

Earths ROtation: Extra info

• Terrestrial planets move as one solid body (no differential rotation)

• Equator rotates faster than the poles → takes the same amount of time for different distances

Venus Observations

• It appears very bright in the sky.

• Even small telescopes reveal that Venus goes through phases like the Moon.

• Galileo discovered the full range of Venusian phases.

  • Used this observation to argue that Venus orbits the Sun, not the Earth.

• Venus’ surface is hidden by dense clouds.

• Density nearly identical to Earth’s

  • Also similar radius 

Venus Atmosphere

• Clouds reflect ~70% of sunlight

  • Observations become difficult.

  • Surface pressure ~100 times Earth’s.

  • Very different in composition from Earth’s atmosphere.

  • Mainly composed of CO₂ → 96.5% 

  • Phosphene found on venus despite no life

  • Has sulphuric acid rain

  • Taller troposphere than earth - first part of the sky

  • Surface temperature: ~730 K (over 850 °F),

Phosphene

• composed of one phosphorus atom and 3 hydrogen atoms → made industrially or through life 

  • Found on venus despite not having life 

Runaway greenhouse effect

•  a climate process where a planet's atmosphere traps heat, causing temperatures to rise uncontrollably 

• Evaporate water 

Venus Geological Activity

•  relatively high, almost as active as Earth.

  • similar to how Earth might appear without erosion or sediment deposition.

  • No water or ice and low surface wind speeds mean:

    • Very little erosion or weathering → due to high temperatures there can be no water or ice to cause erosion

    • Surface features remain preserved for hundreds of millions of years

• Molten Core: but rotation is too slow to have ionic movement that creates a magnetic field

  • Magnetic field from the solar winds interacting with the ionosphere

Lowland lava Plains

• make up 75% of venus’s surface created by lava eruptions

  • No plate tectonics however → has mantle convections causing crustal stress 

Mantle Convections and Tectonic Forces in Venus

 Convection currents of molten rock in Venus’ mantle push, pull, and stretch the planet’s crust

Tectonic features

Geological structures created by these forces

Rift Valleys

• Places where the crust has ripped apart

Mountain ranges

• caused by tectonic compressions

Venus two main continental-sized highland regions

• Rise above the plains → created by crust compression and maintained by mantle convection 

1. Aphrodite terra

• Largest continent covering one third of the planets circumference 

2. Ishtar terra

• Contains Maxwell Mountains, the highest region on Venus.

  • Peaks rise ~11 kilometers above surrounding lowlands.

  • Named after James Clerk Maxwell, the only male-named feature on Venus.

• Age of Venus’s Surface

• YOUNG SURFACE JUST MEANS RECENT GEOLOGICAL ACTIVITY 

• Impact crater density is used to estimate relative surface ages:

  • Dense atmosphere protects from smaller projectiles 

• Average age of the venusian plains: 300–600 million years

  • Significant and recent geological activity → younger than earths continental crust 

  • Large craters still seem fresh → little erosion

    • SMall impactors burn up and don’t reach the surface

• Global Volcanic Resurfacing Event: Thought to have erased most of the older craters

Subsurface Volcanism and Crustal Bulges

• rising magma can accumulate beneath the crust, causing uplift and bulges

  • Creating Coronae: Large circular or oval features

Venus’s Rotation

• The surface is obscured by clouds, so rotation cannot be observed visually.

• Rotation measured via radar signals bounced off Venus.

  • Radar detected topographical features of venus 

• Rotation period: 243 Earth days on the axis → sidereal day 

  • Slow retrograde rotation may be due to powerful collisions during solar system formation

• Orbital period around Sun: 225 Earth days

• Solar day (Sun returning to same sky position): 117 Earth days

Retrograde Rotation

when an object spins in the opposite direction of its orbital motion or the rotation of its primary body

Radar Maps

• Images are constructed from radar wavelengths 

  • Bright regions indicate rough terrain.

  • Darker regions indicate smooth terrain.

Mars Observations

• Distinctly red in color, caused by iron oxides in its soil.

  • This red color may explain Mars’ historical association with war and blood.

• Telescope resolution limits: ~100 km from Earth, similar to seeing the Moon with the unaided eye.

  • At this resolution, no topographic details (mountains, valleys, craters) are visible.

• Visible features mars features

• Bright polar ice caps

• Dusky surface markings that change with seasons

• Distinct red colour 

  • Caused by the clay and iron oxides in the srufcae

• Half the size of earth 

• Lower density than earth 

Mars Polar Caps

• Southern Cap: Never goes smaller than 350km

  • Below 150Kelvin: Includes water ice and dry ice (CO₂ frozen)

• Northern Cap: Never goes smaller than 1000km 

  • Above 150kelvin in the summer: Only water ice

Mars Atmosphere

• Thin atmosphere

  • <1% of earth atmospheric pressure 

  • Main Composition: 95% CO₂, 3% N₂

  • HIgh wind speeds

  • Causing greatly varying temperatures: 35^oC to -143^oc

  • So cold water and carbon dioxide freezes out of the atmosphere

Dust Devil

•  Dust-filled vortices, created by strong surface heating, are generally smaller and less intense than a tornado

Global Dust storms

Caused by the winds

Runaway refrigerator effect

•  less elements in the atmosphere so the planet is a lot colder

Mars Composition

• Mainly made of silicates, with a small solid metal core

  • Solid core: due to mars being smaller and cooled off quicker

    • No global magnetic field due to no ionic movement in the core

• Low density 

Mars Localized magnetic fields

• Possibly had a global magnetic field that caused this

• the crustal rocks on Mars were magnetized long ago → Leaving magnetic patches

• Mars terrain:

• Heavily created south 

• Young volcanic plains on the north 

Tharsis Bulge

• olcanic system on mars containing the highest peak in the solar system (olympus) 

• south of mars

Valles Marineris

• Caused by the upwelling from the Tharsis bulge creating tectonic cracking of the crust 

  • Has experienced water and wind erosion

• south part of mars

Mars Rotation:

• Rotation period (sidereal day): 24 hours 37 minutes 23 seconds

  • Determined by tracking permanent surface markings over many years (very long time) → using optical wavelengths 

• Orbital period: ~2 Earth years, 687 Earth days

• Rotational axis tilt: ~25°, similar to Earth’s.

  • Causes seasons on Mars.

  • Due to Mars’ longer year , each season lasts ~6 Earth months

• Historical Speculation of Martian Civilization

• Controversy began in 1877 with Giovanni Schiaparelli:

  • Observed faint, straight lines on Mars called “canale” (channels).

    • English translation “canals” suggested artificial origin.

    • Imagination led to the idea of canals as irrigation systems from 

• Percival Lowell and the Martian Canal Hypothesis

  • Lowell (American astronomer, 1855–1916) strongly promoted the idea of intelligent Martians → Claimed canals were constructed to preserve Martian civilization amid deteriorating climate.

• Martian Channels and Gullies: 

1. Outflow channels: from catastrophic flooding from heating

2. Runoff Channels: From ancient storms 

3. Gullies: From underground sources, on the steeples of valleys and craters - Underground lakes on Mars: extremely salty water 

Gullies recurring slope linea

• Dark lines found on gullies, changing by seasonal patterns and temperature flow of surface water 

Halophile

• the only kind of life that would be possible in mars salty water since they love salt

• Ancient Lakes and Glaciers on mars

• Dried out Lake beds: now seen as layered sedimentary rock and hematite spheres 

Hematite Spheres

• Iron oxide compounds that only form in water

Sojourner/ curiosity:

• A mars rover → use solar cells for energy

Martian Rocks

• Come to us from meteorites and not from any return missions 

  • Has a smaller escape velocity → more escapes

  • Has traces of water and carbon → possibility of life in the past

Escape velocity

 Minimum speed needed for a projectile to be free of the gravitational influence of a massive object like a planet

• Kinetic energy is = to potential energy 

Kinetic energy:

• changes from the maximum when it is fired from the surface of the  planet to zero when it has escaped the gravitational influence

Gravitational energy

• Is gained as an object moves further from the planet 

  • Therefore kinetic energy = potential energy 

KEY IDEA

More massive objects have a higher escape velocity → they can hold onto lighter gases a lot easier even when they are heated up