PYTS/ASTR 206 – Venus1z AnnouncementsTA h f HW3 d HW4TA change for HW3 and HW4 Use Priyanka Sharma[email protected]@lpl.arizona.edu Office hours: Tuesday 10.30am-12.30pmRoom 316, Kuiper BuildingKevin will return after becoming Dr KevinKevin will return after becoming Dr. Kevin HW3 available on the website today Due in a weekPYTS/ASTR 206 – Venus2VenusPTYS/ASTR 206 – The Golden Age of Planetary ExplorationShane Byrne – [email protected]/ASTR 206 – Venus3In this lecture…In this lecture…IntroductionzIntroductionz Recap on Venus and its atmosphere Super-rotation Tides and retrograde rotationgz Exploring Venus Surface landers Radar instrumentsz Surface of Venus Geography and topography Volcanoes everywhere Craters (or the lack of them)() Wind actionz Interior of Venus Thin crusts MtifildMagnetic fieldsz History of Venus – controlled by water A habitable start… Where it all went horribly wrong…yg Why the Earth escaped the fate of VenusPYTS/ASTR 206 – Venus4IntroductionIntroductionz One of the largest terrestrial planetsPYTS/ASTR 206 – Venus5z Comparison to the Earth A sister planet?VenusSize 95% of the EarthRoughlyThe SameMass 82% of the EarthDensity5243 kg m-3SameInternalStructureygAbout the same as EarthSolar Distance 0.72 AUYear 225 days, 62% of the EarthEccentricity0.007 (almost zero)RoughlyThe SameOrbity()Circular orbit, like the EarthPYTS/ASTR 206 – Venus6z You can see Venus for up to 3 hours after sunset or before sunrisez The brightest planet It’s covered in very reflective clouds It’s close to the Sun It’s close to usPYTS/ASTR 206 – Venus7z Comparison with the Earth IIHhlditidV i?How much solar radiation does Venus receive? Remember:Solar power = 1367 W m-2/ R2 Venus is 0.72 AU from the Sun: R=0.72SSolar power = 1367 W m-2/0722So: Solar power at Venus is 2637 W m-2(about twice that of Earth)Solar power = 1367 W m-2/ 0.722 …but Venus reflects 59% of this sunlight – thick cloud cover22Venus 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…PYTS/ASTR 206 – Venus8z Differences from the EarthAit l t?tllA sister planet? –not reallyVenusAtmosphere Mostly CO2(Earth = Mostly nitrogen)Pressure 90 bars(Earth = 1 bar)Surface Temp. 750K(Earth = 300 K)()VeryDifferentAtmosphere(Molten rock ~ 1000 K)Clouds Sulfuric acid(Earth = water vapor)Rotation period 224 Days - retrograde(Earth = 1 day)Magnetic field None(E th htfild)VeryDifferentSpin(Earth has a strong field)Surface All volcanic rock(Earth = mix of rock types)VeryDifferentSurfacePYTS/ASTR 206 – Venus9z So Earth and Venus started off with similar compositions and positions in the solar systemin the solar systemz What went wrong for Venus??g The answer is in front of you…PYTS/ASTR 206 – Venus10z So Earth and Venus started off with similar compositions and positions in the solar systemin the solar systemz What went wrong for Venus??g The answer is in front of you… WATER! – History of Venus depends on the history of its waterPYTS/ASTR 206 – Venus11zThe greenhouse effectAtmosphere - recapAtmosphere - recapzThe greenhouse effect Both Earth and Venus are warmed by the greenhouse effect Greenhouse gases stop thermal radiation escaping to space Earth has ~0.01 bars of CO2–Temperature boosted by ~30° C2 py Venus has 86 bars of CO2– Temperature boosted by ~400° CPYTS/ASTR 206 – Venus12z Super-rotationCl d V t t i 4 d !Clouds on Venus rotate in 4 days! People were surprised to learn later that the solid planet rotates only every 224 daysy Atmosphere rotates faster than the planetPYTS/ASTR 206 – Venus13z Venus’s weird rotation….Mtl t tt(dbit) tilkiMost planets rotate (and orbit) anti-clockwise (when viewed from above the North Pole) Venus rotates ‘backwards’Theories?Theories? Giant impact Solar tidesPYTS/ASTR 206 – Venus14z Tidal effects on Spin?Vhh iVenus has a huge massive atmosphere… …and is close to the sunSolar tides can slow Venus’srotationSolar tides can slow Venus s rotation Tidal bulge raised by SunRotation of Venus carries the bulgeRotation of Venus carries the bulge around the planet Attraction 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 retrograderetrogradePYTS/ASTR 206 – Venus15z Atmosphere is very heavy and rotates very quickly in a retrograderotates very quickly in a retrograde direction Drag of atmosphere on the solid planet might have reversed its spin di tidirection This 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…Atmospheric motionSurfaceFriction from atmospheric dragon rough surface z The other possibility is a giant impact reversed Venus’s rotationPYTS/ASTR 206 – Venus16Exploring VenusExploring Venusz Clouds are very opaquez Orbiters use radar to see the surface NASA Magellan mission did the most l t i (19921994)complete mapping (1992-1994) Pioneer Venus (late 1970’s) Venera 15 and 16 (1980’s)zRadar looks off to the sidezRadar looks off to the sidez Light/Dark tones don’t correspond to albedozStrong radar return from:zStrong radar return from: Terrain that has roughness on the scale of the radar wavelength Large-scale slopes facing the ftspacecraftPYTS/ASTR 206 – Venus17z Vertical radar system gathers topographySdd l t fti d hSend radar pulses to surface –timed echoes Converted time delay to distance to figure out where the mountains and valleys arePYTS/ASTR 206 – Venus18z Landed spacecraft hard to do on Venusz Only glimpse of the surface Soviets had 4 successful Venera landings on VenusOnboard experiments found basaltic surfaceOnboard experiments found basaltic surface Dark surface, albedo of 3-10% Surface winds of ~ 0.3-1.0 m/s Surface temperatures of 740 K Landers lasted 45-60 minutesVenera 14 –13 S, 310 E –March 1982PYTS/ASTR 206 – Venus19z Spherical images can be unwraped into a low-res perspective viewz Smooth-ish basaltic rock – low viscosity
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