Giant Planets (Jupiter, Saturn, Uranus, Neptune) physical CharacteristicsJupiter"s orbit(a = 5.2 AU) is past the "gap"of the asteroids. The takes amost 12 planet years to circle the Sunonce. Its eccentricity is a typical value because that planets that the solarsystem, in ~ e = 0.0484.Jupiter"s axis is tilted just 1.3oout of the ecliptic, and also it has actually the faster rotation rate of every one of theplanets, at 9h 50m.Jupiter has four very big moons, all greater than 1500 km in diameter.These are dubbed the Galilean moonsbecause lock were found by Galileo as quickly as he completed his telescopeand turned it on the world in 1610. Jupiter additionally has a huge number(at the very least 20) added moons no one of which are higher than 100 kilometres indiameter. These space likely captured asteroids.Jupiter"s radiusis 71,398 km, or 11.2 time Earth"s radius. That makes its volume(11.2)3 = 1400 times that of Earth.Its bulk density, yet is only about 1330kg/m3.This is considerably less dense than planet (5500 kg/m3)and only slightly denser 보다 water (1000 kg/m3).Jupiter is almost entirely made of gas, about 75% by fixed of hydrogen and24% helium, with only 1% of heavier elements. This is almost exactlythe composition of the Sun, giving an important clue to exactly how Jupiter andthe solar mechanism formed. Jupiter probably has actually a rocky main point amountingto several planet masses.The following layer the end from thecore is fluid metallic hydrogen. Thisexotic kind of hydrogen deserve to only exist at pressures exceeding 4 millionbars. Let"s usage our technique of estimating push from lecture 15 to obtain the corepressure that Jupiter:Pc = (2/3)pGr>2R2= (1.4 x 10-10)r>2R2= (1.4 x 10-10)(1330 kg/m3)2 (7.14x107m)2 = 1.2 x 1012Pa, or about 12 million atmospheres.Liquid metallic hydrogen consistsof separation, personal, instance protons and also electrons, wherein the electrons are able to flowfreely choose those in a metal. In ~ the temperature and also pressure ofJupiter"s internal hydrogen is a liquid, no a gas. The temperaturein this great is fairly high, between 11,000 and also 40,000 K dependingon depth. This metallic class is the source of Jupiter"s solid magneticfield -- 4x10-5T in ~ Jupiter"s surface ar -- around the very same asthat at Earth"s surface, however remember that Jupiter"s surface is lot fartherout indigenous the planet"s center. Earth"s magnetic ar at the distanceof Jupiter"s surface, RJ= 71,400 km, is onlyB = B0(r/RE)-3= (4 x 10-5T)(71400/6387)-3= 2.86 x 10-8T.So Jupiter"s magnetic fieldis part 1400 times larger than Earth"s. This mammoth magnetic fieldtraps substantial numbers that energetic particles, therefore the fragment radiation environmentat Jupiter is extreme. Spacecraft have to be closely hardenedto resist the radiation environment.Above this metallic layeris a great of "ordinary" liquid hydrogen and helium, where the electronsare bound to the protons. This ordinary liquid extends all the wayto near the surface, with a fairly thin great of gas forming cloudsin Jupiter"s atmosphere.The albedo that Jupiter isquite high, in ~ 0.52, offering an equilibrium temperature ofTss =279 (1-A)1/4(rp)-1/2= 279 (0.84) (5.2)-1/2= 103 K.The it was observed temperature ofthe cloud tops, however, is 130 K up to as much as 150 K. This leadsto the conclusion that Jupiter has actually an internalheat source, probably left over from its gravitational contraction.The "self-gravitational" potential energy of a body isU = -GM2/R,which method that together a body contracts(R decreases), the potential energy goes under (gets much more negative).According to the virial theorem, whichwe have actually mentioned summary before, 1/2 that this energy must it is in radiated away,and the remainder goes right into heating the body. Throughout Jupiter"s formation,it should have come to be extremely hot, and also it is now progressively cooling down, butit appears from what we know that Jupiter may still it is in generating heat,perhaps proceeding to contract slightly. Exactly how rapidly should it contractto develop the excess warm that we see? way back in lecture 8 wediscussed the flux the a black body, F = sT4W m-2.This flux that energy, when thought about over the entire surface area the aplanet (4pR2),gives a quantity referred to as the luminosity,L = 4pR2sT4(watts).We will be utilizing this quantitya lot next semester. It defines the full power (energy per unittime) emitted by a spherical body. We expect Jupiter to have actually a surfacetemperature of about T0 =103 K, but it really has actually a temperature ofT= 130 K, so the excess power per 2nd isL = 4pR2s(T4-T04)= 4p(7.14 x 107m)2(5.67 x 10-8)<(130)4-(103)4> = 6 x 1017W.We speculate the excess powercomes indigenous a release of potential energy due to a slow contraction.From the expression because that potential power above, the strength released isL = dU/dt = GM2/R2dR/dt,ordR/dt = l R2/ GM2, = (6 x 1017W)(7.14x107 m)2/ (6.67x10-11)(1.9x1027kg)2 = 0.4mm/yearThus, that does not call for muchcontraction at every to relax the it was observed amount of energy. Still,over a billion years Jupiter would need to contract by 400 km, which seemslike a lot. It might be the the reality is some mix of contractionand left-over heat.More on Jupiter"s magneticfieldOn the side of theplanet towards the sun (the daylight side), the solar wind compresses themagnetosphere of the planet and also limits that is size. The size is determinedby a balance in push in the solar wind and also in the magnetosphere--themagnetosphere is compressed till an equilibrium is reached. Thesolar wind is largely a gas pressure, ns = nkT,while within the magnetosphere that is greatly a magnetic pressure,PB= B2/2m0.where m0= 4p x 10-7H/m is the magnetic permeability of totally free space.In the solar wind, we find that the gas pressure drops off as one overdistance from the sun squared: p ~ 1/r2.From this,we can estimate exactly how much bigger Jupiter"s magnetosphere is 보다 Earth"s,by considering the proportion of gas pressure at Earth"s and also Jupiter"s distance,and the proportion of magnetic pressures of Earth"s and Jupiter"s magnetic fields.This is one of the homework problems. Making use of a stormy estimate fromFig. 4-20 the the text, the Earth"s magnetic ar extends to around 10 RE.We uncover that Jupiter"s magnetic field is about 17 RJin size.Missions:Jupiter ProbeThe Galileo orbiter hadan atmospheric probe that enteredJupiter"s atmosphere in 1995 and radioed ago information around theupper class of clouds. An overview of the cloud geometry is shownhere.It entered into a reasonably dry component of Jupiter"s atmosphere, and also descendedinto the hotterlayers beneath. Jupiter"s cloud tops room the lighterareas, dubbed zones, and also are colder.Darkerareas, called belts, are deeperlayers seen through gaps in the whiter cloudes, and hence room hotter.Auroras-- This photo shows auroras at the north and south poles that Jupiter.If friend look closely, you will view a little dot simply to the left of the auroralovals, in the left-hand image. This small dot is due to Io, the innermostmoon that Jupiter. High-energy particles increased at Io rain downon this spots.Comet Collision with Jupiter Shoemaker-Levy 9
Physical attributesMoving currently out to the far reaches of the solar system, the separations the the planets acquire much larger. Jupiter is at 5.2 AU, but Saturn is almost twice as far, in ~ 9.54 AU. This means it takes nearly 30 years because that Saturn come circle the sunlight once. Uranus is again double as far from the sun as Saturn, at 19.2 AU, and takes 84 year to one the Sun. That is so much from the sunlight that it can not be seen conveniently with the naked eye. Therefore, it to be not discovered until 1781, by william (Wilhelm) Herschel. He originally called the world George! (Georgium Sidus, because that King George III of England). Likewise, Neptune was discovered only in 1846, at a distance of 1.5 times the distance to Uranus, 30.1 AU. It takes 165 year to circle the sunlight once.
The discovery of Uranus was accidental, however the discovery of Neptune was a triumph the celestial mechanics. By studying the orbit of Uranus, very tiny perturbation was discovered independently through J.C. Adams (1843) and also U.J. Leverrier (1846). By using Newtonian celestial mechanics, they were able come predict the mass and also orbit that the perturbing body. In 1846, Johann G. Galle found Neptune in ~ 1o that its predicted location. However, Neptune"s orbit diverged quickly from the orbits predicted by the mathematicians, therefore if it had actually been searched for some years earlier or later, the would have actually been far from its guess location. The text has actually a very interesting story about Galileo in this context. In 1613, some 234 years prior to Neptune"s discovery, Galileo"s illustrations of Jupiter showed an object near Neptune"s predicted position, and also he even detected a little motion of the object through respect to a surrounding star. However, that failed to monitor up ~ above the discovery. All three of this gas giants have orbits of low eccentricity (Saturn and Uranus are nearly identical come Jupiter, with e = 0.056 and also 0.048, respectively, while Neptune is also lower at 0.009), and low orbital inclination (2.49o, 0.77o and also 1.77o, respectively). The inclination of their spin axes, however, room large: 26.7o, 98o, and 29o. The 98o for Uranus, in fact, method that that is virtually lying level in the ecliptic plane, as displayed in the photo below. This method that the sun shines top top one pole for 1/2 that its year (that"s 42 earth years), and then on the various other pole for 42 planet years. This is an infrared picture of Uranus, that rings and moons, bring away by the Hubble space Telescope. Every one of these gas giant planets, including Jupiter, have actually ring systems, although just Saturn"s rings are considerable enough to be seen from Earth. Jupiter"s rings come directly from that moons, and are external its Roche Limit. For Uranus and also Saturn the rings are within the Roche Limit, and also may it is in tidally disrupted bodies, although surprisingly small. The case for Neptune is not so clear. We will comment on planetary ring equipment in a later lecture. To compare of Gas large Sizes and also InteriorsAs the figure listed below shows, Jupiter and also Saturn are much larger 보다 Uranus and also Neptune. The interiors the Jupiter and Saturn are similar, with a thick layer of molecule hydrogen, climate a class of metallic hydrogen at the depth whereby the push is adequate (> 4 million bars). The solid inner core is rock in the case of Jupiter, but is a mixture that ice and also rock in the situation of Saturn. The all at once composition that Saturn is virtually the very same as Jupiter, and hence the same as the Sun, but the reduced pressure the Saturn method that the mass density is actually much less than the of water, at just 680 kg/m3. Uranus and Nepture have bulk densities the 1240 kg/m3 and also 1600 kg/m3, respectively. That is exciting that the thickness falls in ~ Saturn and also then rises again together we go out from the Sun. This more than likely reflects a reduced amount that hydrogen in the outermost planets, which instead are make up much more of heavier ices. What scenario might reason this? Magnetospheres:Each the these outer gas giant planets has actually a magnetosphere. Saturn"s is fairly strong, again likely due to the metallic fluid hydrogen layer, together we saw with Jupiter. The surface magnetic ar is 2.1 x 10-5 T, i m sorry is substantially weaker than Jupiter"s, but certainly stronger than Earth"s. At the distance of Saturn, the solar wind pressure have the right to be fairly variable, i m sorry greatly transforms the dimension of the magnetosphere in a selection from about 20 to 30 RS. Let"s have a basic expression because that the size of a magnetosphere, given the surface magnetic ar of the planet and also assuming the the solar wind pressure drops together 1/r2, where r is the street from the Sun. Remember the a dipole field drops through distance from the facility of a planet as B = BS(r/Rp)-3 (1) where BS is the surface magnetic ar strength, and also Rp is the radius the the planet. We recognize that the magnetosphere will prolong out come a distance wherein the gas and magnetic pressures (proportional come B2) room equal, and that Earth"s magnetosphere extends the end to a street of around 10 REarth. The magnetic field at this street is B = BS(10Rp/Rp)-3 = 10-3BEarth. Because the gas pressure drops as 1/r2, the gas push at a distance rp (expressed in AU) indigenous the sun will be reduced by rp-2, for this reason the magnetic pressure required to complement this is additionally lower through the same amount. The magnetic field strength required is then diminished by the square source of this, or B = 10-3BEarthrp-1. This is the ar strength necessary at a street rp (expressed in AU) in terms of the Earth"s surface ar magnetic field. We require it in terms of the planet"s surface ar magnetic field, which we acquire by equating this expression with equation (1), above, which expresses just how the field falls off through distance native a planet. Therefore we have BS(r/Rp)-3 = 10-3BEarthrp-1 and solving because that r, we obtain the final expression: r = 10 (rp BS/BEarth)1/3Rp. This remarkably straightforward expression provides the dimension of the magnetosphere because that a world of size Rp, a street rp from the Sun, in regards to the planet"s surface magnetic ar strength, BS, and also the Earth"s surface magnetic field strength BEarth= 4 x 10-5 T. For Earth, that course, BS= BEarth, rp= 1, and also Rp= REarth so we have actually r= 10REarth as required. In ~ Jupiter, the surface ar happens come be about the same as Earth"s so we have actually BS= BEarth, rp= 5.2, and also Rp= RJ therefore we have r= 17 RJ together was discussed in the vault lecture. Because that Saturn, we have BS~ BEarth/2, rp= 9.4, and also Rp= RS so we have actually r= 16.7 RS similar to the minimum distance pointed out above. Uranus" magnetic field is strange in the it is not centered on the facility of the planet and also is tilted nearly 60 levels with respect come the axis that rotation. The is probably created by movement at fairly shallow depth within Uranus.
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It"s surface field strength is around the same as Saturn"s, i beg your pardon predicts a magnetosphere the size, r= 21 RU. Likewise, Neptune"s magnetic axis is tilted around 46.8 levels from the axis that rotation.Planetary Probe Missions: Uranus