1. Stephen Eikenberry 21 Feb 2019 AST 2037
Life on Mars
Stephen Eikenberry
21 Feb 2019
AST 2037

2. Life on Mars??
Mars has long been a “favorite” location for extra-terrestrial life

3. Why Mars?
Mass ~0.1 Earth-mass
Radius ~0.6 Earth radius
Axis tilt

4. Why Mars?
Seasonal variations and polar caps

5. Martian “Seasons”
Darkening spreads from pole towards equator as summer comes
This is opposite of on Earth (summer “spreads” from equator towards poles)
But … if water availability limits plant growth, as poles warm, liquid water spreads from poles towards equator
As plants grow, reflectivity of planet surface decreases (??)

6. Water on Mars Polar caps seem to indicate water (??)
Schiaparelli finds “canals” (!)
Apparently, not just plant life on Mars, but intelligent beings with large-scale irrigation for agriculture !!

7. Hold on a second …
Other people see similar shapes on Mars … but no “canals”!

8. Mars Atmosphere Mostly CO2 (OK …)
About 0.6% of the atmospheric pressure of Earth (!)
Temperatures can reach about 65 F
But, mostly more like -150 F
At those temps, CO2 freezes (dry ice)

9. Polar Caps: Redux So … could polar caps be dry ice instead of H20?
YES!!
In fact, the albedo (reflectivity) of the caps is too high for water ice, but matches dry ice nicely
Also, we can measure temps when caps recede/grow  too cold for water, but matches dry ice
Now … there IS water ice on the caps too, under the layer of CO2 ice
But … most of the seasonal variation is in dry ice

10. Seasons: Redux
The “darkening” spread from poles to equator is probably due to dry ice “melting” (reducing the albedo of that region)
But … dry ice doesn’t melt – it sublimates (goes straight from solid to vapor form)
Still disappears and changes albedo
What else … ?

11. Canals: Redux
Closer inspection (with photographs!): no evidence for canals
In fact, at this low pressure, water sublimates as well  no liquid water on the surface of Mars!

12. Mars Overview Slightly smaller than Earth
Rotation period is 24.6 hours - close to Earth
Equator inclined at 24 degrees - close to Earth
Very little atmosphere - 1/150 the pressure of Earth
CO2 (95.3%),nitrogen (2.7%), argon, oxygen, CO, water vapor
Two very small moons

13. Mars – Space Craft Exploration
1965 – Mariner 4, 6 and 7 “fly by” Mars
1971 – Mariner 9 orbits and maps Mars in detail
1976 – Viking 1 lands on Mars
1997 – The Mars Pathfinder places a small rover on Mars
2004-present: Mars rovers

14. Mars’ Surface Polar ice caps – frozen CO2
Northern hemisphere is rolling volcanic planes
Southern hemisphere is heavily cratered highlands
Like lunar maria but larger
Few craters – young (3 billion yrs old)
Older (4 billion yrs old)

15. The Tharsis Bulge is the major geographically feature on Mars
Roughly the size of North America
Lies on the equator
10km high
Less heavily cratered
Young (2-3 billion yrs)
Wide depressions (valleys) lie to east and west

16. Valles Marineris
runs for almost 4000 km along the Martian equator (one-fifth of the way around the planet!)
120 km across at its widest
7 km deep in places
our Grand Canyon would easily fit into one of its side "tributary" cracks
NOT caused by water - due to stretching and cracking when Tharsis bulge formed

17. Analysis of rocks on Mars show they are iron rich
- iron in the soil and oxygen in the atmosphere produce iron oxide
RUST
Mars Pathfinder robot Sojourner
Highly successful mission which sent back lots of pictures of the Martian landscape
1999 Mars Polar Lander failed to make contact

18. Volcanism on Mars Largest volcanoes in the solar system are here
Shield volcanoes
None are known to be currently active but eruptions occurred 100 million years ago
Mars has a surface gravity only 40 percent that of Earth, and its volcanoes rise roughly 2.5 times as high because of this.
Olympus Mons on Tharsis slope

19. Water on Mars? Yes – but long ago Runoff channels Outflow channels
About 4 billions years ago Mars had a thicker atmosphere, warmer surface, and liquid water.
Yes – but long ago
Runoff channels
Found in southern highlands
Extensive river systems (like Earth)
Carried water from highland to valleys
Outflow channels
Caused by flooding
Found at the equator
Formed about 3 billions year ago

21. What happened to the water?
4 billion years ago - Martian climate begins to change
Running water (that formed runoff channels) freezes into permafrost (water ice just below surface) and polar caps
Remains frozen for a billion years
Volcanic activity heats large regions of the surface
Melts the permafrost
Flash floods create outflow channels
Volcanic activity slows down and water refreezes