Lecture #21: The Martian Climate Evidence for climate change Did it rain on Mars? Can you have a snowball fight on Mars? Similarities to variations in Earth's climate... Reading: Chapter 10.4 The Main Point Today Mars is a cold, dry, barren world. But there is evidence that Mars 3 to 4 billion years ago may have been a much more Earth-like planet Astro 102/104 1 Astro 102/104 2 Mars ~3 billion years ago? Cold Average temperature: -60 C Mars Today Bone Dry Equivalent to a global layer of only a few microns of liquid H 2 O Lifeless, as far as we can tell Viking was sensitive to ppb levels of organics No ozone layer: Sun's UV gets to surface Astro 102/104 3 Warm Thicker atmosphere, more greenhouse effect Wet More water, in liquid form? Hospitable? Same ingredients for life as early Earth? The Climate of Mars has Changed Drastically This is a THEORY: What's the evidence? Astro 102/104 4 1
Evidence for Mars Climate Change Valley Networks (a.k.a. "Runoff Channels") Heavy erosion of old craters (degraded rims, no ejecta blankets) Presence of surface and subsurface ice (abundant "stored" water?) An Earthlike Mars? Can we find evidence that Mars really had an Earthlike environment? The search takes resources like money, people, time, equipment, technology,... How much should we devote to this search?? Astro 102/104 5 Astro 102/104 6 Martian Channels Outflow channels Hundreds of km long, tens of km wide Contain clear signs of fluid (water ) erosion Contain evidence of catastrophic flooding Source areas: collapsed terrain Formed by rapid melting of subsurface ice? How? Volcanism? Impacts? OLD 2.5-3.5 b.y.? Channel Streamlined flow features Area of Collapse Drainage: S to N Downhill (North) Astro 102/104 7 Martian Channels Valley Networks a.k.a "runoff channels" Only tens of km long, a few km wide Direct evidence of fluid erosion rare Caused by sapping (undermining)? VERY OLD 3.5 b.y. +? Mostly found in the "stubby" ends ancient S. highlands Mars dendritic Earth Astro 102/104 8 2
Sapping Valleys grow by headward undermining of more easily eroded layers: sapping On Earth, underground liquid water is involved On Mars, more likely to be underground water ice Valleys formed by sapping look very different from those formed by runoff Until recently, there has been little geologic evidence for features formed by rainfall on Mars... But then where do these sediments go? Astro 102/104 9 We are learning more, as new missions give us better resolution and coverage of the surface... Still, the state of our ignorance about Mars is profound...but then what are these? Mars Odyssey THEMIS image, near Valles Marineris Astro 102/104 10 Mars Earth Polar Layered Deposits Evidence for cyclical climate change on Mars Many years of warmer, dustier conditions Accumulation of dark, dusty airfall layers in the ice Then, many years of colder conditions Less dust accumulation, brighter, icier layers From the thickness of the layers (tens of meters) and an assumption about the rate of dust accumulation, we can estimate how long it took to form each layer: 10 5 to 10 6 years Darker layer (more dust, less ice) Brighter layer (less dust, more ice) etc... Astro 102/104 11 N. Polar layers in Viking image Trough is about 500 m deep Each layer is about 50 m thick Layers about 10 m Thick could be detected from initial Mars Global Surveyor images... Layers only a few meters thick can be detected from more recent Mars Global Surveyor images Astro 102/104 12 3
Liquid Water on Mars? Can liquid water eist on Mars today? Probably not, according to the phase diagram of water Phase of water (solid, liquid, or vapor) depends on Pressure & Temperature Important concept, not well described/discussed in the tetbook... Layering has had a comple geologic history! MRO/CTX image March 8, 2007 Astro 102/104 13 Vapor Liquid Triple point T T=273K (0 C) P=6.1 mbar Solid (ice) If the temperature on Mars P is not > 273 K and the pressure is not > 6.1 mbar, Astro 102/104 no liquid water is possible 14 But then how can we eplain the evidence for very recent liquid water on the surface from these kinds of MGS images?? T > 273 K and P > 6.1 mbar? Other processes?? Astro 102/104 15 MGS evidence of recent Astro 102/104 16 water flowing on Mars? Malin et al. Science, Dec. 2006 4
Mars Rover Discoveries! There was liquid water on or very near the surface of Mars early in the planet s history and for long periods of time... But: Eactly when? For how long? Implications? Opportunity in Victoria crater Spirit and Opportunity are still going strong, still trying to help us rewrite your tetbook... Astro 102/104 17 Spirit: 1488 sols Spirit Astro 102/104 Opportunity: 1465 sols 18 in salty soils more ice Mars Odyssey Orbiter Results less ice Solid, Liquid, or Gas? Evidence for subsurface Hydrogen! (water ice?) Evidence for variations in Astro 102/104 Thermal infrared emission (different surface minerals?) 19 Astro 102/104 20 5
Digression: Snowballs on Mars? Q: Could you have a snowball fight on Mars? A: Sadly, no. Compressing snow on Earth turns some of the snow into liquid water, which "cements" the snowball... On Mars, the phase remains solid, whether H 2 O or CO 2 This also means: no skiing on Mars :( no ice skating on Mars :( Astro 102/104 21 Climate Change on Earth and Mars Significant and cyclic climate changes have occurred on Earth (e.g., ice ages; Lecture 12) These climate changes are thought to be caused by variations in Earth's orbital parameters Earth's polar ais precession: ~26,000 year timescale Changes in Earth's tilt: ~ 41,000 year timescale Changes in Earth's eccentricity: ~100,000 year timescale The same kinds of orbital variations occur for Mars: Cyclic climate changes there too? Astro 102/104 22 Summary There is very good evidence that the Martian climate was very different 3-4 b.y. ago than today Valley networks, suggesting subsurface ice or water Outflow channels, indicating huge floods Polar layered deposits, suggesting cyclic changes Mars climate changes may be caused by the same astronomical orbit variations that are thought to cause major changes in Earth's climate Amazingly, liquid water may be stable near the Martian surface today, despite contrary predictions Major implications for life on Mars... (Part 4...) Astro 102/104 23 Net Lecture... IN-CLASS EXAM #2! Closed book, independent work Review the assigned reading Review your lecture and section notes Understand any problems you had with homework assignments or lecture topics No electronic devices allowed Bathroom breaks are not allowed during the eam Astro 102/104 24 6