Astronomy - Other Planets of the Solar System - Quick Guides

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Study GuideAstronomy–Other Planets of the Solar System1. MarsMars is amedium-sized rocky planet, often called theRed Planetbecause of its reddish surface.The colorcomes from iron-rich dust that covers much of the ground. Today, Mars isgeologicallyquiet, meaning there are no active volcanoes. Scientists believe the last volcanic activity ended about1.5 billion years ago.

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Study Guide1.1Early History and MagneƟc CluesMars doesnothave a global magnetic field like Earth. However, spacecraft have discoveredstripedpatterns of magnetismon its surface. These stripes have opposite magnetic directions and look verysimilar to the magnetic patterns found on Earth near mid-ocean ridges.These patterns tell scientists that long ago:•Mars likely had amolten iron core•The mantle wasmoving and convecting•Plate-tectonic-like activitymay have occurred early in the planet’s historyAs Mars cooled, these processes stopped.1.2Extreme Surface FeaturesMars has thelargest elevation differencesof any rocky planet in the solar system.•In thenorthern hemisphere, there is a huge crater about1,300 km wide, with a floor10 kmbelowthe average surface level.•In contrast, Mars is home toOlympus Mons, thelargest volcano in the solar system.Olympus Mons•Height:25 km•Type:Shield volcano•Diameter:600 km•Aboutthree times widerthan the largest similar volcano on Earth (in Hawaii)Shield volcanoes form whenthin lava flows easily, spreading out over large areas.1.3Northern vs. Southern HemispheresMars looks very different depending on where you are:•Northern HemisphereoCovered mostly bysmooth plainsoShaped by volcanic lava flows

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Study Guide•Southern HemisphereoMucholder surfaceoHeavilycratered, showing billions of years of impactsThis difference tells scientists that volcanic resurfacing mainly affected the north.1.4Weathering, Deserts, and CanyonsMars shows clear signs ofweathering and erosion, even though liquid water is not present on thesurface today.•Cratered regionsshow long-term erosion•Large desert areasare covered in sand dunes•Winds move dust around, causingseasonal changesin appearanceValles MarinerisOne of the most dramatic features on Mars isValles Marineris, a massive canyon system:•Length:4,000 km•Located near the equator•Includes many smaller side canyonsScientists think it formed when theTharsis regionbulged upward due to movement of moltenmaterial beneath the surface and then cracked apart. Unlike Earth’s rift valleys, this canyon wasnotformed by plate separation.1.5Evidence of Ancient WaterAlthough liquid water does not exist on Mars today, many surface features suggest it once flowedthere:•Teardrop-shaped islands•Dry river channels•Flood plainsAny water remaining today is likelyfrozen underground, trapped aspermafrostor frozen into rocks.

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Study Guide1.6Ice Caps and SeasonsMars haspolar ice capsthat grow and shrink with the seasons.•Average temperature:220 K (−60°F)•Seasonal variation:±30 KThe ice caps are made mostly offrozen carbon dioxide (dry ice), with some water ice mixed in.Seasonal Ice Movement•Innorthern spring, carbon dioxide ice sublimates (turns directly from solid to gas) andmoves south•Insouthern spring, the process reversesDust left behind by sublimating ice formslayered, terraced patternsaround the poles.1.7Thin but AcƟve AtmosphereMars has avery thin atmosphere, with surface pressure only about1% of Earth’s. This is surprisingbecause Mars has enough gravity to hold onto an atmosphere.Possible reasons for atmospheric loss include:•A massivemeteor impactlong ago•Erosion by the solar wind, especially after Mars lost its magnetic fieldAtmospheric Composition•95% carbon dioxide•3% nitrogen•1.5% argon•Small, seasonal amounts of water vapor, oxygen, and heliumEven though the atmosphere is thin, it can still produce:•Fast winds•Planet-wide dust storms, High clouds, especially in the morningAt an altitude of50 km, Mars’s atmosphere is actuallydenser than Earth’s atmosphereat the sameheight.

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Study Guide1.8Interior StructureInside, Mars has the familiarcrust–mantle–core structureseen in rocky planets. Itslow averagedensity (about 3.9 g/cm³)suggests asmall iron core. There isno evidence of current tectonicactivity.1.9Moons of MarsMars hastwo small, irregularly shaped moons:Phobos•Size: about28 × 23 × 20 km•Orbits very close to Mars•Slowly spiraling inward•Expected to crash into Mars or break apart in about100 million yearsDeimos•Size: about16 × 12 × 10 km•Orbits farther away than PhobosBoth moons:•Are heavily cratered•Always keep the same side facing Mars•Are likelycaptured asteroids, not moons that formed with the planet

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Study Guide2. JupiterJupiter is thelargest planet in our solar system. It is so massive that it containsabout two-thirdsof all the planetary massin the solar system (excluding the Sun). Because of its size andappearance, Jupiter is one of the easiest planets to spot in the night sky.2.1Appearance and AtmosphereJupiter appearsreddish-brownand is covered withdark beltsandbright bandsthat wrap all theway around the planet. These arenot solid surfaces. Instead, they arethick layers of cloudsmoving through Jupiter’s atmosphere.•Thebright bandsform whenwarm, light-colored gas risesfrom deep inside the planet.•As this gas reaches higher altitudes,ultraviolet (UV) light from the Suncauses chemicalreactions.•These reactions createdark hydrocarbons, sometimes calledphotochemical smog.•Over time, the gas cools, becomes heavier, andsinks back down, creating a constant cycleof motion.2.2Fast RotaƟon and StormsJupiter spins extremely fast, completing one rotation inabout 10 hours. This rapid spin causes twoimportant effects:1.Equatorial bulge–The planet is wider at the equator than at the poles.

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Study Guide2.Strong Coriolis effect–Moving gases are deflected east or west, shaping the clouds intolong horizontal zones.This effect also causes powerful storms. The most famous one is theGreat Red Spot:•It is agiant cyclonic stormthat has lasted forat least 400 years.•It is about35,000 km wide, large enough to fit Earth.•Its cloud tops rise8 km higherthan nearby clouds.•Winds inside the storm reach speeds of500 km per hour.•The storm slowly drifts but never disappears.2.3Chemical ComposiƟon of the AtmosphereJupiter’s outer atmosphere is made mostly of light gases:•Hydrogen–60%•Helium–36%•Neon–2%•Water vapor–0.9%•Small amounts ofammonia, methane, and argonThe planet’s reddish color comes from:•Acetyleneformation•Phosphorus compoundsreleased from phosphine gasIn the upper atmosphere, clouds form indistinct layersmade of:•Ammonia•Water•Ammonium hydrosulfide

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Study Guide2.4Exploring Jupiter’s InteriorIn 1995, theGalileo probeexplored theouter few hundred kilometersof Jupiter’s atmosphere.Scientists also learned more when fragments ofComet Shoemaker–Levy 9crashed into Jupiter in1994.However, Jupiter’sdeep interior cannot be directly observed. Scientists study it by using:•Jupiter’smean density(about1.3 g/cm³)•Knownphysical laws2.5Inside Jupiter: From Gas to Metal•Theouter layersof Jupiter are made of gas.•Deeper inside, pressure becomes extremely high.•Under these conditions,hydrogen atoms break apart, and their electrons move freely.•This form of hydrogen behaves like a metal and is calledmetallic hydrogen.Because metallic hydrogen conducts electricity:•It createsstrong electrical currents•These currents generate apowerful magnetic field•The magnetic field is tilted10° from Jupiter’s rotation axis2.6MagneƟc Field and AurorasJupiter’s magnetic field is thestrongest of any planet. Around the planet are huge radiation belts,much larger than Earth’s Van Allen belts.•Charged particles from the Sun get trapped in these belts.•When they follow magnetic field lines toward the poles, they createbright aurorasinJupiter’s atmosphere.

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Study Guide2.7Core and Deep InteriorCloser to Jupiter’s center:•Temperatures and pressures are even higher.•Scientists believe there may beicy materialsand asolid rocky core.•The exact structure is still uncertain because small changes in assumptions can lead todifferent results.2.8Temperature and Energy SourceThe temperature of Jupiter’s upper atmosphere is about125 K. This temperature is controlled by:•Absorbing energy from the Sun•Releasing heat as thermal radiationJupiter also emits:•Radio waves, caused by lightning•Energy from interactions between its magnetic field and its moonIoOverall, Jupiter gives offabout twice as much energy as it receives from the Sun. This means itmust have aninternal energy source.2.9Why Jupiter Produces Extra EnergyThe most likely explanation isgravitational contraction:•Jupiter is slowly shrinking as gravity pulls it inward.•It shrinks by about3 centimeters per century.•This slow contraction releases energy as heat.Another way to think about it:•Jupiter is still losing heat left over from its formation.•As it cools, pressure decreases and the planet continues to shrink.

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Study GuideThis table summarizes important information such as:•Size and mass•Density and rotation speed•Distance from the Sun•Orbital period and tilt3. Saturn3.1Meet SaturnSaturn is thesecond largest planetin our solar system. In many ways, it is similar to Jupiter, butthere is one feature that makes Saturn instantly recognizable—itsbeautiful system of rings. Theserings are made ofthousands of thin, concentric bandsthat surround the planet and make it one ofthe most stunning sights in space.

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