Lecture 20 Stagnant Worlds Moon and Mercury 04 08 2014 SURFACES AND THEIR STORIES The surfaces of planets and moons tell stories their features are messages from the past Geoglogy is the study of the surface and interior of the Earth Planets and Moons Surface features are caused by processes o Above Volcanism Impact cratering varied sizes from different size impactors Eruptions of Lava form of erosion Outgassing forms secondary atmosphere Erosion modification by ice water lava sand dust or wind Demonstrated in river deltas the Grand Canyon and glaciers o Interior Tectonics motions of crust or plates convection cells circulate below but close to the surface MOON Craters everywhere therefore it is an old surface o Heavy Bombardment 4 billion years ago o Recent lava flow 3 48 years ago Near side the side we see o Highlands light colors o Mare Maria as plural dark color Moon has been geologically dead sicne the maria formed more than 3 billion years ago Far side Mostly highlands which are too high for internal lava flows to reach Micrometeorites sand sized particles from space meteors from Earth Venus and Mars rain directly on the surface of the airless moon gradually pulverize the surface rock which explains why the lunar surface is covered by a thin layer of powdery soil MERCURY Craters everywhere some with strange hollows o Caloris Basin huge impact which is half the size of Mercury s radius o Scarps vast cliffs wrinkles in crust possibly by contraction which means that Mercury is shrinking Impact craters and volcanism on Mercury impact craters visible almost everywhere indicating an ancient surface Craters are less crowded together than the craters in most ancient regions of the Moon suggesting that molten lava later covered up some of the craters formed during heavy bombardment Tectonic Evidence of Planetary Shrinking tremendous cliffs is evidence of a type of tectonics different from any other terrestrial world Vertically faces up to 3 or more km high and typically run for hundred of km Formed when tectonic forces compressed the crust causing the surface to crumple o Mercury surprisingly has large iron core therefore gained and retained more internal heat from accretion and differentiation than the moon This heat cause Mercury s core to swell in size mantle and lithosphere contracted along with core which closed off any remaining volcanic vents ending period of volcanism SPACE MISSIONS USA Europe Japan Moon o Water in permanently shadowed craters o President Bush s Space Exploration Initiative o Permanent human presence o President Obama put it all on hold Mercury o NASA s Mariner 10 1974 1975 o NASA s Messenger fly by s entered orbit in March 2011 o ESA Japan s BepiColombo 2 spacecraft next decade BU Participation o Moon LCROSS Crash Experiment February 2009 o Moon and Mercury Professor Fritz and Professor Clark BepiColombo Mendillo Group Ground based observations EXOSPHERE region or height in an atmosphere where gases escape Exosphere of Moon exosphere is located at the surface so the velocity of a particle at the surface is equal to or greater than the escape velocity o Surface Sputtering Source and Loss of Processes on the Moon and Mercury o Some of gas released long ago from volcanic activity is stripped off by solar wind but it would have been lost to thermal escape anyway Mercury cannot hold much of an atmosphere because its small size and high daytime temperature mean that nearly all gas particles eventually achieve escape velocity The moon is smaller in size gives it a lower escape velocity but it is also cooler than Mercury Gases escape about as easily on both worlds Ice in Polar Centers there cannot be liquid water on the Moon and Mercury because of the lack of significant atmospheric pressure water cannot remain in liquid form Ice might reside in the permanently shadowed craters near the poles deposited by comet impacts BU IMAGING SCIENCE RESULTS Sodium Gas Observations Moon s atmosphere mapped to 20 times the size of the moon Mercury s atmosphere gets extended to a comet like tail out of 1 000 times the size of its radius which is the role of Radiation Pressure from solar photons Lecture 21 Earth s Siblings Mars and Venus 04 08 2014 NEWS ARTICLES Mercury is getting smaller in size Cosmic Background Radiation 3 kelvin remnants and evidence of Big Bang Inflation Space Ripples COMMON FEATURES OF MARS AND VENUS Atmosphere is mostly Carbon Dioxide CO2 Surfaces with fantastic features o Venus The Hot House Planet radar maps Few craters which are all recent Volcanoes that are possibly active Minimal Erosion due to hot stifling and stagnant atmosphere o Mars The Freeze Dried Planet pictures Giant features Valles Marineris Giant volcano Olympus Mons Evidence of water wherein they found a river bend going downhill within shadowed craters WHY IS VENUS SO HOT Runaway Greenhouse Effect Albedo A reflectivity of the surface the higher the reflectivity the less sunlight observed o A I 1 amount reflected o 1 A I 0 amount absorbed o I reflected radiation Surface radiates energy depending on its temperature the surface temperature can be calculated o Higher reflectivity means that there is more CO2 in the atmosphere which enhances greenhouse effect whereas cloud decrease effect o Without greenhouse effect temperature Earth would be closer to that of Venus because the clouds in Venus prevents sunlight to penetrate MARS AN ABODE OF LIFE Surface features suggest running water a warmer and wetter past Inner Solar System o Mercury and Moons surface boundary exosphere o Venus dense CO2 Earth O2 N2 Mars thin CO2 Secondary atmosphere Gain outgassing evaporation Losses condensation Size matters o Internal heat outgassing volcanism o Gravity retention of gasses Atmosphere pressure o Venus 90 x Earth o Mars 0 01 x Earth Thin atmospheres have weak greenhouse effect so H2O freezes CLIMATE CHANGE ON MARS Causes Axial tilt with respect to orbit around the Sun that is elliptical o 23 degrees seasons o 0 degrees poles are always cold CO2 and H2O always frozen o 60 degrees severe seasons summer pole very war CO2 ice and water evaporate greenhouse effect stronger Why would the tilt change o Gravitational perturbations from Jupiter when it is closer o No stabilizing effect by moons o Collisions Changes in tilt occur on 10 000 1 000 000 years WHAT GEOLOGICAL PROCESSES HAVE SHAPED MARS Impact cratering much of the southern hemisphere has relatively high elevation and is scarred by numerous large impact