1. Chapter 7c Mars: Freeze-dried Image from: http://pds.jpl.nasa.gov/planets/welcome.htm

2. Mars Orbital distance: –227 940 000 km (1.52 AU) –2 nd most eccentric Year: –686.971 d Day: –1.025 d Temperature: –Max: 35°C (95 °F) Summer –Min: −125 °C (-193 °F) winter Diameter: –6794 km Density: –3.933 g/cm 3 Composition: –Iron/nickel/sulfur core, rock Axial Tilt: 25.1 o Moons: two (may be captured asteroids) Other: –Has seasons –Largest volcano in solar system

3. 7.3 Mars: A Victim of Planetary Freeze-drying Our Goals for Learning What geological features tell us that water once flowed on Mars? Why did Mars change?

4. Mars vs. Earth 50% Earth’s radius, 10% Earth’s mass 1.5 A.U from the Sun Axis tilt about the same as Earth. Similar rotation period. Orbit is more elliptical than Earth’s: seasons more extreme Thin CO 2 atmosphere: little greenhouse

5. What geological features tell us water once flowed on Mars?

6. Surface of Mars appears to have ancient river beds

7. Condition of craters indicates surface history Eroded crater

8. Closeup of eroded crater

10. Volcanoes…as recent as 180 million years ago…

11. Past tectonic activity…

12. Low-lying regions may once have had oceans

14. Opportunity Spirit

15. 2004 Opportunity Rover provided strong evidence for abundant liquid water on Mars in the distant past. How could Mars have been warmer and wetter in the past?

16. Today, most water lies frozen underground (blue regions)… Some scientists believe accumulated snowpack melts to carve gullies even today

17. Why did Mars change?

18. Would “terraforming” Mars work? Yes No Rovers?Rovers?

19. What have we learned? What geological features tell us that water once flowed on Mars? Dry river channels, rock- strewn floodplains, and eroded craters all show that water once flowed on Mars, though any periods of rainfall seem to have ended at least 3 billion years ago. Mars today still has water ice underground and in its polar caps, and could possibly have pockets of underground liquid water.

20. What have we learned? Why did Mars change? Mars’s atmosphere must once have been much thicker with a much stronger greenhouse effect, so change must have occurred due to loss of atmospheric gas. Much of the lost gas probably was stripped away by the solar wind, which was able to reach the atmosphere as Mars cooled and lost its magnetic field and protective magnetosphere. Water was probably also lost because ultraviolet light could break apart water molecules in the atmosphere, and the lightweight hydrogen then escaped to space.