Was Mars’ early climate warm or cold?

1. Was Mars’ early climate warm or cold? Megan Cartwright & Jan-Oliver Kliemann March 4th, 2004

2. The Problem • Present Mars is dry and cold (p~6mbar, T~220 K) • But: There are features on the surface of Mars which favor the former presence of liquid water. • A warmer climate would be needed at about 3.8 Gyr ago • But: The sun was weaker by 25-30% then Branching Dendritic Valley Network (Viking 084A47)

3. A good amount of complexity

4. The Combatants Ice-cold Jan Hot Megan

5. The Show • Round 1: A stronger Sun • Round 2: Influence of the Obliquity of Mars • Round 3: A strong greenhouse effect • Round 4: Valley network – different explanations • Conclusion & Future Missions

6. A stronger sun • New Solar Model for a more massive sun: • Upper limit on flux is fixed by the planetary constraint that all planetary H20 would not be lost on Earth • Lower limit on flux is based on the assumption that annual average surface temperatures on Mars should have been at least 273K at the end of the heavy bombardment (~3.9Gyr ago). • Leads to a flux which is 13% greater than the standard solar model predicts and an initial solar mass between 1.03-1.07M(sun)[Whitmire et al, 1995] • Lithium is depleted by 2 orders of magnitude in solar photosphere • Can be explained if the sun had an initial mass of 1.04M(sun) because the Lithium would convect into a region with higher temperatures which could destroy 99% of the initial Lithium. • Agrees with observations of mass-loss rates in solar-type dwarfs

7. A warmer Sun for Mars? No. • The standard solar model was derived including evidence from several measurements • It agrees with nuclear physics, space physics and astrology • The influence of mass in solar flux is huge: • F ~ M 4.75 • Only 5% more mass would mean 103 times more solar wind mass flux and 25% more light intensity at Earth • Is it really a good idea to tackle the standard solar model based on needs for climatic models on planets?

8. The Show must go on • Round 1: A stronger Sun • Round 2: Influence of the Obliquity of Mars • Round 3: A strong greenhouse effect • Round 4: Valley network – different explanations • Conclusion & Future Missions

9. Higher Obliquity as an explanation • GENESIS v.2.0 simulates the effect of high-obliquity on planets [Jenkins, 2001] • It found that at higher obliquity • Mars received higher insolation at high latitudes for a surface of bare soil • Higher insolation at the poles would provide higher greenhouse gas concentrations • To produce valley formation Mars would need some combination of elevated greenhouse concentrations and an obliquity greater than 54 degrees

10. Chaotic Obliquity • The obliquity is chaotic (i.e. unpredictable) • The Genesis model does not include eccentricity

11. Chaotic Obliquity • The obliquity is chaotic (i.e. unpredictable) • The Genesis model does not include eccentricity • A higher obliquity would not increase the total amount of energy that is going to Mars • Even if we agree with a 70o obliquity we still have to agree with the greenhouse model that is assumed

12. The Show must go on and on • Round 1: A stronger Sun • Round 2: Influence of the Obliquity of Mars • Round 3: A strong greenhouse effect • Round 4: Valley network – different explanations • Conclusion & Future Missions

13. What was the mechanism for warming? • Greenhouse Effect • Solar radiation became trapped by CO2 and H20 atmosphere and reflected back towards surface • Thus warming the surface • But is that enough to warm the surface for liquid water? • We need a few bars to produce the necessary warming.[Haberle, 1998]

14. Added Effects for Greenhouse • CO2 ice cloud cover • CO2 ice cloud formation would IR scatter back towards surface • This effect could increase surface temperatures by 60K if the cloud opacity was ~ 10 and cloud cover was 100%. [Forget & Pierrehumbert, 1997] • Other greenhouse gases: • SO2 from volcanism • CH4 NH3 from outgassing, although easily destroyed [Haberle, 1998]

15. Where did Mars’ ancient atmosphere come from? • Volcanism • Tharsis volcanism would have produced large quantities of CO2 • Geochemical analysis of Martian meteorites suggests a water content of as much as 1.8% by weight • Many of the ancient valley networks are seen to preferentially follow the slopes that resulted in the formation of Tharsis, thus Tharsis is from Noachian epoch.

16. Ancient atmosphere cont’d • Cometary impacts • Analysis of isotope ratios of heavy noble gases suggest much of planets’ volatiles could have come from comets • although we don’t know the role of supply and removal [Jakosky & Philips, 2001]

17. Where did the early atmosphere go? • Impact erosion: • Large impacts (asteroids and comets) can eject an early atmosphere because of Mars small size (small surface gravity) • Impacts will not change the isotope ratios, but by analyzing the D/H ratio in old Martian meteorites, we find that the initial D/H was twice as much as the terrestrial value which suggests a loss of 2/3 of Mars’ H. • Probably was dominant loss mechanism early in Noachian epoch

18. Where did the early atmosphere go? • Lost to space • Dynamo turned off most likely in Noachian epoch. • Allow solar wind to strip ions from the upper atmosphere • Theoretical models are currently uncertain about importance • But isotope measurements indicate stripping has occurred and was significant. An example is the ratio of 38Ar/36Ar is 30% greater on Mars than elsewhere in the solar system. • Indicates a loss between 50-90% of the atmospheric species to space • Probably was dominant removal mechanism in late Noachian epoch. • [Jakosky & Phillips, 2001]

19. Where did the early atmosphere go? • Weathering: • Process in which atmospheric CO2 becomes carbonate mineral • Found in Martian meteorites • Although with an atmosphere of several bars we should expect to see a layer of carbonate hundreds of meters thick and we don’t yet, so the relative rate of this loss is unknown • Lost to polar caps • Due to these losses the atmospheric pressure would fall and the CO2 ice cap may have grown until the CO2 ice buffer state was achieved. (i.e. snowball Mars) Most likely occurred at the end of the Noachian period. [Jakosky & Phillips, 2001]

20. Where is the Carbonate? • Outgassing of water vapor and sulfates • may have combined and thus destroyed the carbonate • Sulfuric acid and UV radiation • can both break down upper layer of carbonate • Current remote sensing can only see top few cm • Large deposits may be present but can’t detect due to particle size or texture • Soil formation changes • It’s possible the soils formed now are more volumetrically abundant than those formed in early Mars’ history [Craddock & Howard, 2002]

21. CO2 Ice Clouds: warming or cooling? • Most greenhouse models assume 100% cloud coverage • Slight changes in optical depth of clouds can result in cooling • Changes in height of clouds could also result in cooling • Greenhouse models show that multiple cloud decks weaken the greenhouse effect • Too thick clouds become more opaque to the incoming IR and cool the planet • Greenhouse models that operate with mixtures of gases closely rely on the ratio of those gases • We still haven’t found ANY carbonate on the surface of Mars [Mischna et al., Jenkins et al., Yung et al.]

22. The Show continues • Round 1: A stronger Sun • Round 2: Influence of the Obliquity of Mars • Round 3: A strong greenhouse effect • Round 4: Valley network – different explanations • Conclusion & Future Missions

23. Valley network = Warm Climate? • The valley network is not a proof for a warm climate • There are two possible solutions for a cold valley network forming: • The valley networks were not formed by water at all – The White Mars model [Hoffmann, 2000] • The valley networks formed by groundwater sapping [Goldspiel et al., 2000] [Squyres et al., 1994]

24. 1. “White Mars” model • Valley networks have formed by CO2 gas explosions: • The lithostatic pressure releases a little (below the stability of liquid CO2) • Liquid CO2 flashes to dry ice and vapor • Pressures of 5-50 bars drive debris sheet over the surface that carve channels out • The abundance of CO2 and the absence of carbonates and water seem to contribute to the model [Hoffmann, 2000]

25. 1. “White Mars” model [Hoffmann, 2000]

26. White Mars: reasonable approach? • Heat flow (Q) and thermal conductivity (k) play an important role in the depth of liquid water. • Hoffman assumes global Q=40 mW/m2, k=2.0W/m-K • These values are not appropriate for an early Mars • Q ~ 120 mW/m2 because Q decreases with time (depends on initial energy of accretiation and radioactive decay) • k~.4-.8W/m-K for a C02 cryosphere (depends on pore space) • New evidence from Tuesday indicates the former presence of liquid water on Mars [Urguhart & Gulick, 2003]

27. White Mars: reasonable approach? [Urguhart & Gulick, 2003]

28. 2. Groundwater sapping • Liquid water under the surface (geothermally heated) could be responsible for the erosion features that we see

29. 2. Groundwater sapping • The features seen for groundwater sapping are very similar to surface runoff features • The efficiency of this process is sufficient to explain the large networks on Mars [Goldspiel et. Al, 2000] http://erode.evsc.virginia.edu/marssap.htm

30. Groundwater sapping

31. An example of groundwater sapping – Nirgal vallis [Jaumann, Reiss, 2002]

32. Linear profile [Jaumann, Reiss, 2002]

33. An example of groundwater sapping – Nirgal vallis [Jaumann, Reiss, 2002]

34. Width/Length ratio [Jaumann, Reiss, 2002]

35. An example of groundwater sapping – Nirgal vallis [Jaumann, Reiss, 2002]

36. Reply to groundwater sapping • Their typical V-shaped cross-section requires gradual rather (surface runoff) than a catastrophic formation process • Erosion rates were different in the Noachian age (~1000 times larger than in later epochs) as seen on ancient impact craters. • The largest craters and basins are severely degraded • Ejecta deposits, crater rims, and central peaks have all been removed • The scarcity of craters smaller than 15 km diameter suggests they have been removed entirely.[Jakosky & Phillips, 2001] • Dendritic networks of valleys appear similar to those formed on Earth by surface water flow and groundwater sapping • Ground water flow, recharge, and erosion are closely related to precipitation and surface runoff on the Earth. They do not occur independently of each other which is often disregarded for Mars. [Craddock & Howard, 2002]

37. Conclusion & Future Missions • A heavier sun is unlikely • Greenhouse climate models give proof either way • The surface features on Mars were most likely caused by water erosion but the mechanism (rainfall, groundwater sapping) remains inconclusive • We need a series of missions to Mars which will focus on early climate related issues (i.e. carbonates, seismographs etc).

38. The End Sorry, Martians, but we need a little bit more information…

39. References • Craddock, R.A., Howard, A.D.: The case for rainfall on a warm, wet early Mars. Journal of Geophysical Research107, 21-1-36 (2002) • Forget, F., Pierrehumbert, R.T.: Warming Early Mars with Carbon Dioxide Clouds that Scatter Infrared Radiation, Science 278, 1273-1276 (1997) • Goldspiel, J.M., Squires, S.M.: Groundwater Sapping and Valley Formation on Mars, Icarus 148, 176-192 (2000) • Haberle R.: Early Mars climate models, Journal of Geophysical Research103, 28467-79 (1998) • Hoffman, N.: White Mars: A New Model for Mars’ Surface and Atmosphere Based on CO2 , Icarus 146, 326-342 (2000) • Jakosky, B.M., Philips R.: Mars’ volatile and climate history. Nature412, 237-244 (2001) • Jaumann, R., Reiss, D.: Nirgal Vallis: Evidence for Extensive Sapping, Lunar and Planetary Science XXXIII 1579 (2002) • Jenkins, G.S.: High-Obliquity simulations for the Archean Earth: Implications for the climatic conditions on early Mars, Journal of Geophysical Research 106, 32903-13 (2001) • Mischna, M.A., Kasting, J.F., Pavlov, A., Freedman, R.: Influence of Carbon Dioxide Clouds on Early Martian Climate, Icarus 145, 546-554 (2000) • Murray, N., Holman, M.: The role of chaotic resonances in the Solar Systems, Nature410, 773-779 (2001) • Squires, S.M., Kasting, J.F.: Early Mars: how warm and how wet?, Science265, 744-750 (1994) • Urquhart, M.L., Gulick, V.C.: Plausibility of the “White Mars” hypothesis based upon the thermal nature of the Martian subsurface, Geophysical Research Letters 30 (12), 1622-1625 (2003) • Whitmire, D.P., Doyle, L.R., Reynolds, R.T., Matese, J.J.: A slightly more massive young Sun as an explanation for warm temperatures on early Mars, Journal of Geophysical Research100, 5457-64 (1995) • Yokohata et al. Role of H2O and CO2 ices in Martian climate changes. Icarus 159, 439-48 (2002) • Yung, Y.L., Nair, H., Gerstell, M.F.: CO2 Greenhouse in the Early Martian Atmosphere: SO2 inhibits Condensation, Icarus 130, 222-224 (1997)