1. The Inner Planets

2. The Inner Planets to Scale
3,031 mi ,521 mi ,926 mi ,222 mi
5.4 g/cm g/cm g/cm g/cm^3

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)
They are called terrestrial (rock) planets
Why do the inner planets share these similarities?

4. Earth Only planet known to have liquid water
Only planet known to have life
What features of Earth allow it to sustain life?
Earth

5. Mercury Diameter: 3,031 mi Orbits once every 88d Rotates once in 59d
The smallest planet
Orbits once every 88d
Rotates once in 59d
How long is it from Sunset to Sunrise?
Virtually no atmosphere
Closest to the sun

6. Mercury’s Surface What causes these craters?
Why do we see so many of them?

7. Temperature Extremes on Mercury
Daytime Temp: 900°F extremely hot
Nighttime Temp: -250°F-extremely cold
Why the temp. extremes?
Long time without sunlight (~176 d)
No atmosphere to hold or transfer heat

8. Venus Similar in size and density to Earth Earth’s twin
Nearest planet to Earth
Thick atmosphere (95XEarth) of CO2
Hottest surface of any planet
Completely covered in clouds of sulfuric acid
How can you study the surface the clouds?

9. 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?

10. “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?

11. Venus Through the Clouds
You look through the clouds – with RADAR!
Bounce sound waves off the surface & study the echo

12. Mars Red/Pink color Called the red planet
caused by “rust in the dust” (iron in rocks)
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

13. Martian Valcanoes
Largest (extinct) volcano in the S.S. – Olympus Mons-9 miles high!
Shield volcano, similar to Hawaii
Astronomers think Mars lacks tectonic plate movements; how could this explain the large volcanoes?

14. 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?

15. 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?

16. Martian Water? Martian Life?

17. Life on Mars?

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19. Inner Planets