astro 101 lecture 12 the jovian planets...
TRANSCRIPT
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Astro 101 Lecture 12 The Jovian Planets
2-28-2018
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Jupiter, Saturn, Uranus and NeptuneASTR-101Section 004
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Bulk Properties of Terrestrial and Jovian Planets• All Jovian planets have strong magnetic fields• Jovians are about as dense as water (1000 kg/m3)• Very cold• Way more massive
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Discovery of the Jovians
• Jupiter and Saturn have been know since antiquity.
• Jupiter is the third brightest object in our sky (Moon and Venus are brighter)
• Saturn can be seen with binoculers
• Uranus was discovered in 1781 and was the first planet to be “discovered”. It was almost named George after the king of England.
• Neptune was discovered after a careful study of Uranus’s orbit.
• Astronomers found that in order to explain why Uranus’s orbit was deviating from Newtonian mechanics, another planet father out must be pulling on it.
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Jupiter
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• Jupiter is composed of 71% hydrogen, 24% helium, and 5% all other elements by mass. Has a higher percentage of heavy elements compared to the Sun
• Rotates so rapidly that the planets are noticeably flattened – Jupiter has 98% of the angular momentum of the solar system!
• The visible “surfaces” of Jupiter are actually the tops of clouds
• The rapid rotation of the planets twists the clouds into dark belts and light zones that run parallel to the equator
• The outer layers of the atmospheres shows differential rotation, meaning the equatorial regions rotate slightly faster than the polar regions.
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• Strong convection currents cause the bands of color seen on Jupiter’s upper cloud layer. Due to Jupiter’s rapid rotation, these belts and zones east and west.
• None of the gases in the clouds can explain the color of Jupiter’s belts.
• These strong convective currents create a complex cloud chemistry that is very sensitive to pressure and temperature, which leads to the cloud coloration.
• Underlying these bands is a zonal flow region that is a stable east-west wind that flows at 500 km/h (310 mph)
Jupiter’s Weather
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Optical – colors dictated
by how molecules
reflect sunlight
Infrared - traces heat in
atmosphere.
So white colors from cooler, higher clouds, brown and red from
warmer, lower clouds.
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Storms of Jupiter
• Because of Jupiter’s differential rotation and strong convective currents, massive storms occur on Jupiter’s surface.
• The Great Red Spot has existed for at least 300 years.
• It is sustained by large scale atmospheric motion.
• Jupiter’s storms are similar to hurricanes that we experience on earth.
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The internal heat of Jupiter and Saturn has a major effect on the planets’ atmospheres
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Saturn
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• Saturn’s atmosphere is similar to Jupiter’s, except pressure is lower.
• Cloud layers are wider than Jupiter’s because Saturn’s gravity is 2.5 times weaker.
• Lower pressure implies a lower temperature. This has caused much of the helium to liquefy.
Saturn’s Atmosphere
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• Saturn has planet wide storms that are similar to thunder storms
• The white clouds seen are from warm methane gas come up from deep inside the planet.
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• Earth-based observations reveal three broad ringsencircling Saturn
• Saturn’s rings of are composed of numerous particles of ice and ice-coated rock ranging in size from 1 um to about 10 m
• Jupiter’s faint rings are composed of a relatively small amount of small, dark, rocky particles that reflect very little light
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Uranus
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• The blue color of both Uranus and Neptune is due to their high concentration of methane.
• Methane absorbs long wavelengths like red much better than it short wavelengths like blue.
• Uranus has a very thick haze above its atmosphere, thus making it hard to observe any features. This is due to it being the coldest Jovian.
• The rotation was measured by watching storms as they moved across the surface of the planet
Uranus’s Atmosphere
Sun
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Neptune is a cold, bluish world with Jupiterlikeatmospheric features
• Much more cloud activity is seen on Neptune than on Uranus.
• This is because Uranus lacks a substantial internal heat source.
• White methane clouds can be seen in stormy areas
• Neptune has equatorial winds that blow at 2000 km/h and are retrograde relative to the rotation of the planet.
• Neptune and Pluto have intersecting orbits.
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Uranus and Neptune each have a system of thin,dark rings
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• Because of the large pressure and temperature of Jupiter’s and Saturn’s interior, hydrogen and helium compresses into its metallic state.
• No direct information is available about Jupiter’s interior, but we know that it has a solid rocky core.
• Jupiter flattens because of its fast rotation. It is 7% fatter around the middle.
• It would be much more pronounced if the planet lacked a solid core.
• The metallic hydrogen and helium are great conductors and are the source of the planet’s magnetic field
Jupiter’s and Saturn’s Interior
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• Both Uranus and Neptune may have a rocky core surrounded by a mantle of water and ammonia
• Water and ammonia have been compressed into a slushy.
• Uranus and Neptune contain a higher proportion of heavy elements than Jupiter and Saturn
• No metallic hydrogen and helium. The pressure is not large enough, ammonia water slushy may be able to explain the existing magnetic field
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The magnetic fields of both Uranus and Neptuneare oriented at unusual angles
• The magnetic axes of both Uranus and Neptune are steeply inclined from their axes of rotation
• The magnetic and rotational axes of all the other planets are more nearly parallel
• The magnetic fields of Uranus and Neptune are also offset from the centers of the planets
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Jupiter’s Magnetic Field• At the surface of the Jupiter, the
magnetic field is 14 times strong than on earth. Enough to stop a pacemaker from working.
• When Jupiter’s size is taken into account, the magnetic field strength is ~20,000 times stronger than earth.
• It extends well into Saturn’s orbit 4 AU away.
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Jovian Internal Heating
• If no internal heating occurred, jovians would radiate back all of the suns energy.
• Jupiter emits twice as much energy, Saturn emits three times as much energy, and Neptune emits 2.7 times as much energy.
• Uranus is a cold gas planet.
• Jupiter and Neptune create their heat because they are still contracting.
• Saturn has a much more complicated heating mechanism that involves liquefied helium raining down into the interior. Not well understood.