Slide 1VenusSlide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36PYTS/ASTR 206 – Venus1AnnouncementsTA change for HW3 and HW4Use Priyanka Sharma[email protected]Office hours: Tuesday 10.30am-12.30pmRoom 316, Kuiper BuildingKevin will return after becoming Dr. KevinHW3 available on the website todayDue in a weekPYTS/ASTR 206 – Venus2PTYS/ASTR 206 – The Golden Age of Planetary ExplorationShane Byrne – [email protected]/ASTR 206 – Venus3In this lecture…In this lecture…IntroductionRecap on Venus and its atmosphereSuper-rotationTides and retrograde rotationExploring VenusSurface landersRadar instrumentsSurface of VenusGeography and topographyVolcanoes everywhereCraters (or the lack of them)Wind actionInterior of VenusThin crusts Magnetic fieldsHistory of Venus – controlled by waterA habitable start…Where it all went horribly wrong…Why the Earth escaped the fate of VenusPYTS/ASTR 206 – Venus4One of the largest terrestrial planetsIntroductionIntroductionPYTS/ASTR 206 – Venus5Comparison to the EarthA sister planet?VenusSize 95% of the EarthMass 82% of the EarthDensity 5243 kg m-3About the same as EarthSolar Distance 0.72 AUYear 225 days, 62% of the EarthEccentricity 0.007 (almost zero)Circular orbit, like the EarthRoughlyThe SameInternalStructureRoughlyThe SameOrbitPYTS/ASTR 206 – Venus6You can see Venus for up to 3 hours after sunset or before sunriseThe brightest planet It’s covered in very reflective cloudsIt’s close to the SunIt’s close to usPYTS/ASTR 206 – Venus7Comparison with the Earth IIHow much solar radiation does Venus receive?Remember:Venus is 0.72 AU from the Sun: R=0.72So:Solar power at Venus is 2637 W m-2 (about twice that of Earth)…but Venus reflects 59% of this sunlight – thick cloud coverVenus actually absorbs only: 0.41*2637 W m-2 = 1082 W m-2 Not that different than a clear day at Earth’s equator!People thought that Venus might be some sort of tropical paradise…Nobody could see the surface though…Solar power = 1367 W m-2 / R2Solar power = 1367 W m-2 / 0.722PYTS/ASTR 206 – Venus8Differences from the EarthA sister planet? – not reallyVenusAtmosphere Mostly CO2 (Earth = Mostly nitrogen)Pressure 90 bars(Earth = 1 bar)Surface Temp. 750K(Earth = 300 K)(Molten rock ~ 1000 K)Clouds Sulfuric acid(Earth = water vapor)Rotation period 224 Days - retrograde(Earth = 1 day)Magnetic field None(Earth has a strong field)Surface All volcanic rock(Earth = mix of rock types)VeryDifferentAtmosphereVeryDifferentSurfaceVeryDifferentSpinPYTS/ASTR 206 – Venus9So Earth and Venus started off with similar compositions and positions in the solar systemWhat went wrong for Venus??The answer is in front of you…PYTS/ASTR 206 – Venus10So Earth and Venus started off with similar compositions and positions in the solar systemWhat went wrong for Venus??The answer is in front of you…WATER! – History of Venus depends on the history of its waterPYTS/ASTR 206 – Venus11The greenhouse effectBoth Earth and Venus are warmed by the greenhouse effectGreenhouse gases stop thermal radiation escaping to spaceEarth has ~0.01 bars of CO2 – Temperature boosted by ~30° CVenus has 86 bars of CO2 – Temperature boosted by ~400° CAtmosphere - recapAtmosphere - recapPYTS/ASTR 206 – Venus12Super-rotationClouds on Venus rotate in 4 days!People were surprised to learn later that the solid planet rotates only every 224 daysAtmosphere rotates faster than the planetPYTS/ASTR 206 – Venus13Venus’s weird rotation….Most planets rotate (and orbit) anti-clockwise(when viewed from above the North Pole)Venus rotates ‘backwards’Theories?Giant impactSolar tidesPYTS/ASTR 206 – Venus14Tidal effects on Spin?Venus has a huge massive atmosphere……and is close to the sunSolar tides can slow Venus’s rotationTidal bulge raised by SunRotation of Venus carries the bulge around the planetAttraction between the bulge and the Sun slows down Venus’s rotationEffects of tides - View from the sideSolar tides slow down Venus’s rotation, but don’t explain why it’s retrogradePYTS/ASTR 206 – Venus15Atmosphere is very heavy and rotates very quickly in a retrograde directionDrag of atmosphere on the solid planet might have reversed its spin directionThis only works because….The atmosphere is very massive and has lots of momentum…Solar tides already did most of the work…We have billions of years to get this done…The other possibility is a giant impact reversed Venus’s rotationSurfaceAtmospheric motionFriction from atmospheric dragon rough surfacePYTS/ASTR 206 – Venus16Clouds are very opaqueOrbiters use radar to see the surfaceNASA Magellan mission did the most complete mapping (1992-1994)Pioneer Venus (late 1970’s)Venera 15 and 16 (1980’s)Radar looks off to the sideLight/Dark tones don’t correspond to albedoStrong radar return from:Terrain that has roughness on the scale of the radar wavelength Large-scale slopes facing the spacecraftExploring VenusExploring VenusPYTS/ASTR 206 – Venus17Vertical radar system gathers topographySend radar pulses to surface – timed echoesConverted time delay to distance to figure out where the mountains and valleys arePYTS/ASTR 206 – Venus18Landed spacecraft hard to do on VenusOnly glimpse of the surfaceSoviets had 4 successful Venera landings on VenusOnboard experiments found basaltic surfaceDark surface, albedo of 3-10%Surface winds of ~ 0.3-1.0 m/sSurface temperatures of 740 KLanders lasted 45-60 minutesVenera 14 – 13 S, 310 E – March 1982PYTS/ASTR 206 – Venus19Spherical images can be unwraped into a low-res perspective viewSmooth-ish basaltic rock – low viscosity magmasVenera 9 – A Blockier AppearanceVenera 13PYTS/ASTR 206 – Venus20Earth has obvious topography dichotomyHigh continentsLow ocean floorsVenus has a unimodal hypsogramNo plate tectonicsSeveral volcanic plainsSeveral crustal plateaus Surface of VenusSurface of
View Full Document
Unlocking...