The Inner Planets

The Inner Planets to Scale

3,031 mi 7,521 mi 7,926 mi 4,222 mi

5.4 g/cm3 5.2 g/cm3 5.5 g/cm3 3.9 g/cm^3

Inner Planet Similarities

• All are a few thousand miles across

• All are made of rock, with an iron core

• All are dense (b/c made of rock)

• Why do the inner planets share these similarities?

Earth

• Only planet known to have liquid water

• Only planet known to have life– What features of Earth allow it

to sustain life?

Mercury• Diameter: 3,031 mi

– The smallest planet

• Orbits once every 88d• Rotates once in 59d

– How long is it from Sunset to Sunrise?

• Virtually no atmosphere

Mercury’s Surface

• What causes these craters?• Why do we see so many of them?

Temperature Extremes on Mercury

• Daytime Temp: 900°F• Nighttime Temp: -250°F• Why the temp.

extremes?– Long time without sunlight

(~176 d)– No atmosphere to hold or

transfer heat

Venus

• Similar in size and density to Earth

• Nearest planet to Earth

• Thick atmosphere (95XEarth) of CO2

• Completely covered in clouds of sulfuric acid– How can you study the

surface the clouds?

Venus’ Surface• Sent spacecraft to take pictures from the surface• Lasted 2 hr 7 min

– Found out it was 865°F at the surface!– Why so hot?

“Greenhouse Effect”

• CO2 reflects heat back to the surface

• Sunlight gets in, heat can’t escape – just like a greenhouse

• Similar to greenhouse effect on Earth, only 10,000X more CO2– What would Al Gore say?

• Heat & pressure destroy spacecraft sent to the surface– How then can you study its surface?

Venus Through the Clouds• You look through the clouds – with RADAR!

• Bounce sound waves off the surface & study the echo

Mars

• Red/Pink color caused by “rust in the dust”

• 68°F to -200°F• Seasons like Earth’s• Thin CO2 atmosphere

– If CO2, why isn’t Mars hot like Venus?

– Low pressure means water cannot be a liquid

Martian Valcanoes

• Largest (extinct) volcano in the S.S. – 9 miles high!

• Shield volcano, similar to Hawaii• Astronomers think Mars lacks

tectonic plate movements; how could this explain the large volcanoes?

Martian Canyons

• Largest canyon – 3,000 miles long and 5 miles deep– Rocks shrink when

they cool. Astronomers think Mars may have cooled quickly after its formation; how might this be used to explain the large canyon?

Martian Surface• Many spacecraft sent

to the surface• Searched for life,

evidence of liquid water– Why would astronomers

be interested in liquid water?

– If liquid water can’t exist at low pressure, why do astronomers still look for evidence of liquid water on Mars?

Martian Water? Martian Life?

Life on Mars?