Questions about Mars

1. Questions about Mars • What happened to the water on Mars ? • Has all the water escaped or is it hidden in the ground and polar caps? • What is the present and past climate of Mars • What is the crustal history of Mars • How and when did Mars experience differentiation of the surface? • What caused the surface of Mars to split into two halves • old southern highlands, young northern lowlands? • Did the crust of Mars stop evolving, and if so when & why? • If Mars used to have a thick atmosphere made of CO2, where is all the CO2 now? • if CO2 went into the ground, where is the carbonate on the surface of Mars? • (Unlike Hyrodgen or Helium, CO2 does not readily escape from an atmosphere)

2. About Water on Mars There is no running water on the surface of Mars today, but the presence of water in the atmosphere suggests that water cycles between the ground and atmosphere today. Fog rises out of the ground and condenses back again, and water vapor in the atmosphere condenses and evaporates. • Evidence for running water includes, • river channels • frozen, icy polar caps • clouds • fog. • Much of the water of Mars is frozen into the ground, and can only be released when Mars experiences a warming change in climate. • Mars is much smaller than the Earth, and Mars is farther from the sun that either the Earth or Venus. These facts mean that the surface of Mars cooled off more rapidly than the other two planets. This picture is from the recently discovered gullies which form evidence of water running on Mars today.

3. Terrestrial Water Cycle On Earth, rivers serve the purpose of draining water from basins and transporting it downstream as part of the water cycle. Rivers and their tributaries carry water from higher elevations to the sea. Streams and tributaries are called a drainage network or a "network" for short. The shape of the network can take on a number of different patterns, including the one shown here. Without adequate drainage, basins and plains would flood. On Earth, networks seem to follow certain rules which are illustrated in the drawing: • all streams can only flow one way, namely downstream • small tributaries connect to larger ones • eventually the network terminates at the ocean (there are no oceans on Mars)

4. Martian Water Cycle • Although there seem to be rules which govern how a network provides drainage on Earth, there is no reason that those rules should be the same for Mars. Indeed, scientists think that some of the rules may be very different for Mars. • For example, on Mars, water may be forced out of the ground and from the main stem into the tributaries. This would be different from the normal path on Earth. A habitat for life requires a water cycle, not just the presence of water. On Mars the question is, does the water truly cycle from the ground to surface and back to the ground.

5. Martian Water Cycle, continued • It may not be sufficient to have water in order to have life on Mars. • It may require that water cycle between the atmosphere, surface, and underground. • Living things use up available nutrients in stagnant water. • Is there evidence that water cycles on Mars? The question remains unanswered.

6. What a surprise Europa turned out to be - is there an ocean? The physical properties of a surface are understood via spectral measurements in different wavelength regimes. • The surface is by no means one of homogeneous ice. • Endless, repeated passes of the surface under different lighting conditions are required to learn about it: • A flyover's purpose is to show a region of the satellite during continually changing lighting conditions, with solar illumination coming from a variety of directions and elevations above the surface. With the Sun in different positions, features with different orientations become more evident. With the Sun low to the surface, brightness variations are dominated by the shadows cast by landforms. In contrast, with the Sun high in the sky, brightness differences are dominated by the intrinsic differences in reflectivity of the surface materials. The combination of illuminations maximizes the ability to characterize landforms and to separate the effects of topography from differences in reflectivity. In this picture of the surface of Europa can be seen the results of complementary instrument measurements. To understand the physical properties of the surface, repeated observations under differing lighting conditions must be made The surface of Jupiter’s moon Europa, as imaged by the Galileo spacecraft. Composition, material units, and roughness of surface features are illustrated.

7. Does Europa have an Ocean? There are several pieces of evidence to consider: • Conamara Chaos region is characterized by a thin dirupted ice crust that suggests shifting ice plates much like those found in the Earth’s arctic landscapes.

8. Ocean? • The lack of craters on the surface • surface is 10 MY or younger? • rarity of craters determined by (>24 months of) careful study of reflected light from the surface • Analysis of small cracks adjacent to large topographic loads implies a layer of brittle ice, less than 1 km thick above the supposed ocean

9. Ocean? continued • Preponderance of internally caused pits, moats, and domes • depressions formed locally where the ice has collapsed due to internal geologic activity.

10. Ocean? continued • water has reached surface to form once-again-frozen “ponds” • there are many examples of “lobate” flow • Magnetometer detected near surface currents • implies the presence of convecting/circulating currents in a salty ocean • what is needed to form a magnetic field? • electric currents, => electrically conducting material in motion • electrically conducting materials include: • iron (iron core of a planet) • salt water

11. Two possibilities with regard to these observations • (1) An ocean exists and explains all the features that have been discovered. Such an ocean would have to be roughly near the surface (found at no more than 500 km below the surface). The crust and lithosphere of Europa would exist over the ocean. • If the crust and lithosphere are not too thick, light from the sun will likely shine through this layer into the ocean beneath. On Earth, we know that there are life forms which can exist under conditions such as these. • (2) There is no ocean and these observations are the result of the presence of processes in warm soft ice wherein, if there is melting to make water, the melting takes place only in small areas. • Galileo's discoveries have encouraged us to think that there might be life elsewhere in the solar system.

12. Jupiter’s moon Io • The only place in the solar system besides Earth for active volcanism • Sulfur frost on the surface • Hot lava flows of iron and sulfur • Reminiscent of Earth’s earliest environment

13. Io Io - a thin atmosphere, no plate tectonics • extensive volcanism • surface recycling • patchy atmosphere • frosty surface • the constant lava flows in place are suggestive of the early Earth

14. Boy was that Sulfur Good! Common Sulfur bearing minerals on Earth • H2S hydrogen sulfide • FeS2 iron sulfide (pyrite) • PbS lead sulfide • S2 sulfur • SO2 sulfur dioxide • SO4= sulfate • (CaSO4.2H2O) - gypsum Sulfur eating bacteria on Earth metabolize sulfur without oxygen or photosynthesis (Thiobaccillus) • SO4= S S = • What if such bacteria were introduced on Jupiter’s moon Io?

15. Saturn’s Titan -- Climate & Plate Tectonics • The Atmosphere • The Surface • The Interior

16. Titan AtmosphereSimilarities to early Earth atmosphere? • Main constituent is nitrogen gas (N2) • Contains a few percent of methane gas (CH4) • Both being continuously broken apart by • Solar ultraviolet photons • Bombarding electrons from Saturn’s magnetosphere • Cosmic rays • Recombination and chemistry: hydrocarbons (the building blocks of life) • Surface pressure ~60% greater than Earth’s • However, temperatures very low (<-180°C)

17. The Atmosphere Comparison of Titan and Earth

18. The Surface • What might the surface of Titan be like? • liquid (ethane) • Solid (hydrocarbons)

19. Titan Surface • Liquid water? (only if/near thermal vents) • Ethane ocean? (not according to HST) • Ethane/methane lakes? (yes - methane in atmosphere would otherwise disappear)

20. Questions about Titan to be addressed by Cassini • Mapping by RADAR (also visible and infrared?) • Mapping of landing site by Descent Imager • Surface Science Package studies on surface • Topography • Liquid or solid? • Composition • Temperature • Pressure • Surface radius • Illumination

21. The Interior - potential for a “driver” of surface activity? • Little information on interior structure. • Density 2.0 g cm-3: largely water ice? • No magnetism? • Methane? • Ammonia? • Rock? • Temperatures? • Mascons?

22. Titan Interior • Extrapolation from other environments? • Possibility of subsurface activity?