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?