the valley network record on mars (class 1). challenges for our understanding: climate models have a...
Post on 15-Jan-2016
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The Valley Network Record on Mars (Class 1)
Challenges for our understanding:• Climate models have a very hard time raising the Martian
surface temperature significantly, even with a thick CO2
greenhouse
Standard stellar evolution models suggest that the solar output was ~70% current at 4 Gya
• Mineralogy of surface preserves a record of “easy to weather” volcanic minerals from Early Mars (olivine, pyroxene)
• But mineralogy now also reveals a bunch of weathering products!
Cold today, cold tomorrow, warm 3.8 billion years ago?
How do valleys on Earth compare to Mars?
On Earth:
Erosion linked to surface precipitation and runoff is very important to the shape of the land at local-to-mega-regional scales*,**
* even to the point of coupling tectonics to erosion!
** fluvial activity sets the broad form of most surfaces
Drainage density is usually >>0.07 km/km2; actual drainage densities are a result of a complicated competition between hillslope (diffusive) and valley-forming (advective) processes. This competition is linked to climate…
(Think back to first class).
Yemen
How do valleys on Mars compare to Earth?
On Mars:
• Valley formation does not appear to have modified the mega-regional scale topography…
• Local densities can reach near-terrestrial values, but smallest tributaries are uncommon (Why?)
• Valleys do reach to drainage divides (groundwater alone is not a great explanation)
• Valleys we observe now are likely >3.5+ Gyr old…(What characteristics can we ascribe to this?)
Huygens Crater East Rim Region
40E, 20S
HRSC 0532 MOLA topography
500 km
Naktong Vallis/ Scamander Vallis Mamers Vallis system (after Irwin et al., 2005).
• Some basins appear integrated over length of ~3000-5000 km
• Numerous (200+) hydrologically ‘open’ lakes (lakes with outlets) across Mars
What do we want to know?
• Intensity• Precipitation[?] rates?• Discharges?
• Persistence• Global or local activity?• Long-lived climate or short excursions?• Intermittency? One episode or many? Formation Time
(prime topic of next class)
• Environmental Requirements (and/or) Implications• Is an ‘ocean’ necessary to support a climate where it
rains or snows? Are large lakes good enough?