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Lecture 19 Giant Planets I Great Red Spot Lecture 19 Giant Planets I Great Red Spot Jupiter The largest planet in the solar system Mass = 300 x Earth Mass = 0.001 x Sun Atmospheric Compositions Jupiter Extensive Ring System Mass = 95 x Earth = 1/3 Jupiter Rings can appear to disappear when we see them edge on Uranus is Uranus blue but very bland Mass = 14.5 x Earth = 1/20 Jupiter Lecture 21 Uranus and Neptune Mass = 17 x Earth This is a = 1/18 Jupiter Voyager 2 image of Neptune’s Neptune Great Dark Spot - Blue has now disappeared We will discuss and compare the four Jovian planets together Orbital and Physical Properties Internal Structures Atmospheres Magnetospheres Satellites Rings !"##"$%#&'()*('+"%$),)-".&"/) Small!"##"$%#&'()*('+"%$),)-".&"/) and rocky - no rings - few satellites Mercury Venus Earth Mars (radar) Jovian Planets Jovian Planets :';$<*/*&+'=$&4'">'()%&*+':';$<*/*&+'=$&4'">'()%&*+' •! !"#$%&'()%&*+,-'".+*/' •! !"#$%&'()%&*+,-'".+*/' ,")%/',0,+*12'3*0"&4' ,")%/',0,+*12'3*0"&4' 5%/,' 5%/,' –!!.6$+*/' –!!.6$+*/' –!7%+./&' –!7%+./&' –!8/%&.,' –!8/%&.,' •–!9*6+.&*' –!9*6+.&*'! !"##$%&'&()%$&(*++",$& •! -).$%&/$0+"123&/"4$%$01&5)(6)+"7)0& •! 8"0#+& •! 9:($%):+&())0+& Knowledge is mostly very recent and derived from US space missions Space Missions To Outer Planets Voyager Spacecraft used the gravity of the planets to reach the outer solar system - a planetary sling-shot !"#$%&'()(*(+( Outer planet arrangement ~ (1970s-1980s) every 175 years! 4 giant planets: Jupiter Saturn Uranus Neptune Orbit the Sun in the outer solar system - beyond the “snow” line - outside the Asteroid Belt and inside the Kuiper Belt !"#$%&#'()*+,-+./0+$.) 1%,-%'#&2'%)3#'/%.)4/&5)6/.&#$7%)&+)82$)#$6)'%92"#&%.:) •! ;5/75)%"%,%$&.)#7&2#""()7+$6%$.%) •! ;5/75)7+,-+2$6.)#'%)<+',%6)<'+,)&5%)%"%,%$&.) •! =&)45#&)'#&%.)&5%)7+,-+2$6.)#'%)<+',%6>) Volatile species will only be stable beyond a “snow line”. This is why the inner planets are rock-rich and the outer planets gas- and ice- rich pink/grey boundary - the snow line Orbital Radii in AU (Earth = 1) Jupiter 5.2 Saturn 9.5 Uranus 19.2 Chance discovery Neptune 30.1 Predicted from gravitational theory !"#$%"&'(')*+,#-' All are fast rotators None of the planetary spins have been braked by tides Mean Densities in g/cm^3 Jupiter 1.3 Saturn 0.7 (less than water) Uranus 1.6 Neptune 2.1 The low mean densities of the giant planets imply that they must be composed mostly of light gases like those in the Sun, that is, Hydrogen and Helium and ice forming gases: Ammonia, Methane and Water Jupiter and Saturn (densities 1.3 and 0.7) are more massive but less dense than Uranus and Neptune (1.6 and 2.1) Jupiter Saturn TextAlmost all H & He, Very little metal & rock (less dense) <50% H & He, the rest hydrogen compounds (water, methane, ammonia), with much ice and some metal & rock (more dense) Compositions are primordial Uranus Neptune Density is the most important clue to composition - but we must allow for the effects of compression The diameter of a hydrogen/helium planet does not increase for ever as the mass is increased Compression of a Hydrogen/Helium Planet More massive planets could even be smaller! Max Radius •! !"#$%&'()*+(,)%"'*()'&(*&)'-.(%/&(0)1&(0$2&( •! 3"%(!"#$%&'($0(45(16'&(1)00$7&(%/)*(,)%"'*( (((89')7$%):6*)-(;61#'&00$6*($*;'&)0&0(%/&(+&*0$:&0(6<(1)%&'$)-($*(%/&( $*%&'$6'=!( Hydrogen and Helium Molecules in Atmospheres Hydrogen Helium Sun 84% 16% Jupiter 86.1% 13.6% Saturn 97% 3% Plus trace amounts of ammonia, methane and water Jupiter is slightly depleted in helium Saturn is strongly depleted in helium Mass-Radius relations for massive planets made of either Hydrogen/Helium, Water or Rock Jupiter and Saturn are mostly hydrogen and helium Uranus and Neptune are half hydrogen and helium and half “ices” ammonia, methane and water How do we know this? How do we know this? Educated guesses about Jupiter’s internal constitution Educated guesses about Jupiter’s internal constitution Educated guesses about Jupiter’s internal constitution We cannot see beneathHow the clouds do we of Jupiter, know but this? we can use external We cannot see beneath the clouds of Jupiter, but we can use external Wemeasurements cannot see beneath to constrain the clouds its internal of Jupiter, properties. but we As can an use example, external measurements to constrain its internalEducated properties. guesses As aboutan example, Jupiter’s internal constitution we now know that the giant planetmeasurementswe emits now its know own to thatheat constrain theradiation, giant its planetinternal emits properties. its own As heat an radiation,example, wewhich now means know thatthat theit is giant hot inside. planet emitsSince itsJupiter own heatand theradiation, Sun originated which means that it is hot inside. SinceWe cannot Jupiter see and beneath the Sun the originated clouds of Jupiter, but we can use external whichfrom similarmeans thatmaterial it is hotat the inside. same Since time, Jupiter a good and initial the assumptionSun originated is that from similar material at the same time,measurements a good initial to constrain assumption its internalis that properties. As an example, from similar material at the same time, a good initial assumption is that they have the same ingredients withtheywe similar now have know proportions.the same that the ingredients giant planet with emits similar its own proportions. heat radiation, they have the same ingredients with similar proportions. (butwhich then means all that planets it is hot inside. would Since have Jupiter the and same the Sun composition originated The planet’s low average mass densityThefrom planet’s indicatessimilar materiallow that average it is at in the fact mass same composed density time, a indicatesgood initial that assumption it is in fact is composedthat largely of hydrogen and helium,The just planet’sas the Sun low is. average mass density indicates that it is in fact composed theylargely have of thehydrogen same ingredients and helium, with just similar as------- the proportions. Sun is. largely of hydrogen and helium, just as the Sun is. The planet’s oblate shape and rapid rotation also tell us indicates = good place to start TheThe planet’splanet’s lowoblate average shape mass and rapiddensity rotation indicates also that tell it usis in fact composed omething about the way it is constructedThe planet’s inside. oblate shape and rapid rotation also tell us omething largely of about hydrogen the way and helium,it is constructed just as the inside. Sun is. omething about the way it is constructed inside. Due to the enormous pressures inside Jupiter, most of the planet’s hydrogen TheDue planet’s to the enormous oblate shape pressures and rapid inside rotation Jupiter, also mosttell us of the planet’s hydrogen is compressed into a liquid metallic Due form, to the and enormous helps account pressures for the inside giant’s Jupiter, most of the planet’s hydrogen isomething compressed about into the away liquid it is metallic constructed form, inside. and helps account for the giant’s strong magnetic field. is compressed into a liquid metallic form, and helps account for the giant’s strong magnetic field. strong Due to magnetic the enormous field. pressures inside Jupiter, most of the planet’s hydrogen All of these constraints have been pieced together to make a picture of Jupiter’s invisible interior. is compressed into a liquid metallic form, and helps account for the giant’s All of these constraints have been pieced together to make a picture of Jupiter’s invisible interior. All strong of these magnetic constraints field. have been pieced together to make a picture of Jupiter’s invisible interior. All of these constraints have been pieced together to make a picture of Jupiter’s invisible interior. How do we know this? Educated guesses about Jupiter’s internal constitution We cannot see beneath the clouds of Jupiter, but we can use external measurements to constrain its internal properties. As an example, we now know that the giant planet emits its own heat radiation, which means that it is hot inside. Since Jupiter and the Sun originated from similarWhere material doesat the same this time, heat a good come initial assumption is that from? they have the same ingredients with similar proportions. The planet’s low average mass density indicates that it is in fact composed largely of hydrogen and helium, just as the Sun is. The planet’s oblate shape and rapid rotation also tell us omething about the way it is constructed inside. Due to the enormous pressures inside Jupiter, most of the planet’s hydrogen is compressed into a liquid metallic form, and helps account for the giant’s strong magnetic field. All of these constraints have been pieced together to make a picture of Jupiter’s invisible interior. @A3%'-)3'+&&#'"'9)3*/&')1'.&"%' How much more heat is radiated than • ! !"#$"%&'()*&'&+&*,-'%."+'%.&-'*&/&$0&'1*)('23+'received from Sun? •! 4)5'(3/.6' In the IR the planets –! 738$%&*'%5$/&'"9'(3/.' are glowing –! 2"%3*+'%.*&&':(&9'"9'(3/.;' •! 4)56'<*"0$%":)+"='&+&*,-' Heat of Formation –! 2:=='/)+%*"/:+,'>738$%&*?' –! 4&=$3('*"$+'>2"%3*+?' Helium is condensing and falling to the center - heating the planet Because helium is raining out in Saturn - and to a lesser extent in Jupiter it means that helium is present in the planetary interior even if it is depleted (relative to the Sun) in the atmosphere Weather on Jupiter and Saturn is controlled by the internal heat sources - no seasonal changes Educated guesses about Jupiter’s internal constitution We cannot see beneath the clouds of Jupiter, but we can use external measurements to constrain its internal properties. As an example, we now know that the giant planet emits its own heat radiation, which means that it is hot inside. Since Jupiter and the Sun originated from similar material at the same time, a good initial assumption is that they have the same ingredients with similar proportions.
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