Planets. Solar System Formation Terrestrial Planets Terrestrial Planet Atmospheres Terrestrial...

Planets

Planets

Solar System Formation

Terrestrial Planets

Terrestrial Planet Atmospheres

Terrestrial Planet Characteristics

Jovian Planets

Trans-Neptunian Objects

Solar System Formation

Solar System

Solar system – consists of six basic categories:

1. Sun (typical small star) 99.9% of the solar system’s mass

2. Planets and their moons (~ 0.1% of the Sun’s mass)

3. Planetesimals (remainder of the planet-forming debris) Asteroids Comets

4. Small debris (includes meteoroids and micrometeoroids)

5. Dust (small particles)

6. Gas Dominated by hydrogen and helium

Solar System

Solar system composition

Solar system composition is the contents of gas cloud that collapsed to form the Sun and other nearby stars

70% H 25% He 5% other stuff

IcesDust grainsGases

Solar System

Early universe composition consisted of only gases

75% H 25% He <0.001% other stuff

3He2D (deuterium, or heavy hydrogen)4Li

Solar System

Planet formation sequence is actually the sequence f the formation of a star and its disk of gas and dust

1. Gas cloud collapse and rotation

2. Condensation and crystallization

3. Pre-solar heating

4. Planetary core formation

5. Gas dispersion and transparent disk

6. Planet stabilization

7. Outer solar system remnants

Solar System

Solar system (star) formation

Star (Sun) forms early but requires time to stabilize

Rotating disk around star shapes the position of the planets Planets form from debris in disk

Planet formation halted by several mechanisms

Some planets change position and energy by dynamical interactions

Remnants (leftovers) still orbiting the Sun

Solar System

Solar system segregation (as star forms and stabilizes)

Star isolated from planets that begin forming due to intense energy, gravitational inflow, and particle wind and radiation outflow

Small and large clumps that will make up larger planetesimals are created in roughly three zones

Interior – hot, dense materials remain Exterior – cold ices and gas remain Distant – bound by gravity but relatively unaffected by solar heat

Planets build (accrete) from smaller planetesimal material Interior – rock and metal planets (terrestrial) Exterior – giant gas and ice planets (Jovian) Distant – ice bodies and comets

Solar System

Final solar system structure

Star dominates entire solar system in mass and energy

Planets are created in violent collisions between small and large bodies

Segregated due to star/Sun heatingNatural accretion of disk material in rotating star

formationPlanets are common

Chaos produces varying size and compositionHigh temperature materials near star Ices and gases beyond “ice line” located between Mars

and Jupiter

Solar System

What was responsible for creating the three planetary zones?

The Sun’s T-Tauri stage created a hot zone nearest the star High radiation and high-velocity outward winds swept most

of the inner solar system clear of material The remainder fell inward, or was left behind as dense, high-

temperature (refractory) debris T-Tauri phase named after the 19th brightest star (Tau) in the

constellation Taurus (Tauri) now going through a similar phase as our Sun passed through 4.6 billion years ago

This created solid planets in a temperate region of the stable Sun Venus Earth Mars

Solar System

Outside this region was the “ice line” sometimes referred to as the frost line or freeze line

Temperatures are well below water ice temperature and ices accumulate on the solid bodies

Located in asteroid belt between Mars and Jupiter

Asteroids inside the ice line have a number of different surface characteristics than those beyond

Outside the Jovian planets are even colder objects that have had only minor heating from the Sun over the 4.6 billion year history of the solar system

Planets

Jovian or Giant planets formed with large cores and huge gas atmospheres Surroundings were not depleted by the Sun’s

strong T-Tauri winds

Composed mostly of hydrogen and helium Inner two (Jupiter, Saturn) are closest to the Sun

and composed of 80-95% gas Outer two (Uranus, Neptune) are rich in ices

Planets

Body Rock/metal % Ices % Gas %

Terrestrial planets (approximate) 70 30 0

Asteroids (approximate) 70 30 0

Comets, Pluto 15 85 0

Jupiter (gas planet) 2 5 93

Saturn (gas planet) 6 14 80

Uranus (ice planet) 25 58 17

Neptune (ice planet) 27 62 11

Terrestrial Planets

Terrestrial Planets

Inner solar system

Terrestrial means “Earth-like”

Composed of rock and metals These are refractory (high-

temperature) materials

Similar orbit planes with slight orbital eccentricity

Smaller rock-metal bodies include many of the asteroids and our Moon

Terrestrial Planets

Formation of terrestrials was by violent collisional heating from impacting planetesimals Planetesimals are asteroids and comets Collisional accretion and impact heating

produced:Liquid metal cores Liquid rock mantle

After major formation events that included the heavy bombardment phase, cooling created a thin, solid crust

Terrestrial Planets

In the early formation stages, the crust was still very hot, but allowed gas and liquids (atmosphere and oceans) to begin accumulating

Cooling increased from accumulating water primarily from cometary impacts on the surface

Liquid mantle remained molten because of its high temperature, and the insulating properties of the light, thin, solid crust

Terrestrial Planets

Materials that remained closest to the hot Sun were the most dense Materials that remained closest to the hot Sun were the most dense and lowest in abundance and lowest in abundance → a→ a simple hypothesissimple hypothesis

Hypothesis test:Hypothesis test: Terrestrial planets farther from the Sun should be larger (closest Terrestrial planets farther from the Sun should be larger (closest

should be smallest)should be smallest) Terrestrial planets farther from the Sun should be lower in density Terrestrial planets farther from the Sun should be lower in density

(closest should be the most dense)(closest should be the most dense) Terrestrial planets farther from the Sun should have a smaller Terrestrial planets farther from the Sun should have a smaller

core/mantle ratio (closest should be largest)core/mantle ratio (closest should be largest)

Terrestrial Planets

MercuryMercury Highest density (except for Earth which is gravitationally Highest density (except for Earth which is gravitationally

compressed) compressed) →→ supports hypothesis supports hypothesis Smallest terrestrial planet Smallest terrestrial planet →→ supports hypothesis supports hypothesis

VenusVenus Lower density than Mercury Lower density than Mercury →→ supports hypothesis supports hypothesis Larger than Mercury Larger than Mercury →→ supports hypothesis supports hypothesis

EarthEarth Highest density, but because of gravitational compressionHighest density, but because of gravitational compression Larger than Venus Larger than Venus →→ supports hypothesis supports hypothesis

MarsMars Lowest density Lowest density → → supports hypothesissupports hypothesis Smaller than Earth Smaller than Earth x does not support hypothesisx does not support hypothesis

Terrestrial Planets

Liquid rock and metal interior allowed segregation of the materials by density (differentiation) Heat from impacts and gravitational compression

melts rocky planets and larger moons Molten planets differentiate in density

Gravity produces buoyancy that floats lighter materials in the liquid state

Liquid metal core is hot and dense, but circulates in a large rotating planet because of low viscosity (low resistance to flow)

Terrestrial Planets

Geodynamo magnetic field theory:

Circulating, conductive liquid metal core generates magnetic fields

First initiated by surrounding magnetic field of Sun

Induced electric current in conductive metal core generated by a weak external magnetic field strengthens planet’s internal magnetic field

Increased magnetic field further increases current

Strong geomagnetic field generated in what is known as the geodynamo process

Terrestrial Planets

Magnetic fields

Liquid metal core must be significant in size (mass Liquid metal core must be significant in size (mass larger than the Moon)larger than the Moon)

Planet must rotate rapidly enough to circulate Planet must rotate rapidly enough to circulate conductive liquid metal core conductive liquid metal core

The exception to this simple geodynamo theory is The exception to this simple geodynamo theory is Mercury which has a very small mass (6% of the Mercury which has a very small mass (6% of the Earth's mass) and a slow rotation rate of 59 daysEarth's mass) and a slow rotation rate of 59 days

Mercury’s small residual magnetic field is most Mercury’s small residual magnetic field is most likely induced by the nearby strong magnetic field likely induced by the nearby strong magnetic field of the Sun, with a core kept liquid by the Sun's of the Sun, with a core kept liquid by the Sun's tidal flexingtidal flexing

Terrestrial Planets

Crust

Thicker crust-to-radius ratio for smaller planets because of their faster cooling Earth's crust about 0.5% of radius Mars' crust 1% of radius Moon's crust about 5% of radius

Thin crust can fracture on larger terrestrial planets if the rotation is fast enough to circulate the liquid mantle that supports the thin crust

Terrestrial Planets

Crust

Hypothesis: Fast rotation and the exchange of heat/mass create a continuous and active surface geology, including:

Quakes VolcanoesMountain and elevated plateausCrustal motion in broad fragments, or plates

(plate tectonics)

Terrestrial Planets

Geological activity from rapid rotation and thin crust

Earth – yes, fast 24 hr rotation period → supports hypothesis

Venus – no, too slow (240 day rotation period)Large mountains and plateaus formed by different

mechanisms → almost supports hypothesis

Mars - no (rapid rotation, but mass is too small) Large mountains and plateaus formed by different

mechanisms → almost supports hypothesis

Mercury - no (slow rotation and too small) → supports hypothesis

Terrestrial Planets

Mantle

Between the light, thin crust and the dense metal core Between the light, thin crust and the dense metal core of the terrestrial planets lies the molten rock mantleof the terrestrial planets lies the molten rock mantle

Composed of various types of rock under tremendous Composed of various types of rock under tremendous pressure from the overlying masspressure from the overlying mass

Tremendous pressure can force the liquid mantle Tremendous pressure can force the liquid mantle (called lava when it reaches the surface) through (called lava when it reaches the surface) through cracks or fissures in the crustcracks or fissures in the crust

Terrestrial Planets

Mantle

For rapidly rotating planets, the movement of the For rapidly rotating planets, the movement of the dense mantle can stretch and/or fracture the thin dense mantle can stretch and/or fracture the thin overlying crustoverlying crust

Any break or weakness in the crust allows upward Any break or weakness in the crust allows upward flow of the liquid rock mantle to the surface = flow of the liquid rock mantle to the surface = volcanoesvolcanoes

Terrestrial Planets

Mantle

Semi liquid (plastic) or liquid molten rock between core and crust

Transfers heat from core to the surface

Thin crust on larger planets allows volcanic activity

Thicker crust and/or slow rotation allows broad, long-term volcanic buildup because the crust has little or no motion

Terrestrial Planets

Volcanic shields and plateaus found on both Mars and Venus, but for different reasons

Mars - rapid rotation Relatively rapid crustal motion and active

fracturingProduced volcanoes on Mars in its early history

(1st billion years)Volcanoes are still active on the Earth

Venus - slow rotation Large volcanic buildup possible such as the large

plateaus on Venus (e.g., Maxwell Montes) and volcanic shields

Terrestrial Planets

Lithosphere

Part of the Earth's solid crust is connected to the upper portion of the mantle, forming the major surface plates that move in an irregular fashion known as plate tectonics

Defining the crust, lithosphere, and mantle is not by the structure but by the type of flow

Upper mantle which includes the lithosphere deforms until fracturing

Layer below the lithosphere known as the asthenosphere has a semi-liquid (plastic) deformation mode

Terrestrial Planets

Earth’s internal structure

Terrestrial Planet Atmospheres

Terrestrial Planets

Atmospheres

Primary Created during the planets’ formation H, He, plus some other atomic gases Dispersed by heat since H and He have low escape

velocity

Secondary added by: Volcanism, impact deposition from comets, asteroids Comets – N2, O2, CH2 Volcanoes - CO2, SO2, H2S, H2O

Long-term atmospheric gas buildup and retention Lighter gases retained according to planetary mass

(escape velocity) and planet temperature

Terrestrial Planets

Atmospheres

Secondary atmospheres remained permanently for Venus and Mars because of their surface inactivity (Mars is small, Venus has slow rotation)

H2O lost in Venus' hot atmosphere and from its lower mass (gravity)

H2O lost from Mars because of its small mass (gravity)

Terrestrial Planets

Atmospheres

CO2 absorbed in Earth's rock crust, mantle, and oceans

O2 was generated by some H2O breakdown, and early biological life

Results of the evolution of the three terrestrial planet atmospheres:

Venus 96% CO2, 4% N2

Mars 95% CO2, 3% N2

Earth 78% N2, 21% O2, 0.04% CO2

Terrestrial Planets – Retained Gases

While the four Giant planets can retain any gas in their atmospheres including hydrogen and helium, the Moon and Mercury cannot retain even the heaviest common gas CO2

Gases retained for a specific planet or moon are represented by the diagonal lines that appear below the planet/moon

Terrestrial Planet Characteristics

Mercury

Mercury

Mercury which is the closest planet to the Sun is also the smallest terrestrial planet

Mass 3.302x1023 kg (0.0553 MEarth) Radius 2,439 km Mean density 5.43 g/cm3

Orbital eccentricity 0.2056 Orbit inclination 7.0o

Semimajor axis 5.791 107 km (0.387 AU)

Mercury

Orbit period - 88.0 days Rotation period - 58.6 days (3:2 orbit to

rotation resonance period due to nearby Sun) Magnetic field - 0.0033 gauss (1% of Earth) Albedo - 10.6% (Earth = 37%, Moon = 12%) Atmosphere - trace (approx. 1,000 kg total,

composed of K, Na, Ar, O, O2, He and other trace gases)

Venus

Venus is the next planet from the Sun and often called the sister planet of the Earth since it is only 5% smaller

Mass - 4.87x1024 kg (81% of Earth) Radius - 6,052 km (95% of Earth) Mean density - 5.24 g/cm3

Semimajor axis - 0.723 AU Orbit period - 224.7 days Rotation period - 243.0 days Magnetic field - Not significant (~10-5 x Earth) Albedo - 75% (Earth = 37%) Atmosphere - 92 bar (92 Earth atmospheres)

96.5% CO2, 3.5% N2

Venus

The surface geology of Venus includes volcanic features that include large elevated plateaus, large and small volcanic cones and shields, and pancake-shaped formations of lava

Features on the surface of Venus indicate an age of only 300-500 million years

This relatively new surface is thought to be from the periodic remelting of the lower crust

Magma would then flow through the cracks, fissures, and craters to cover much of the lower elevations

Earth

Mass - 5.974x1024 kg (1/333,000 MSun) Radius - 6,378 km (equatorial) Mean density - 5.52 g/cm3

Semimajor axis - 1.00 AU Orbit period - 365.24 days Rotation period - 23 hr 56 min (sidereal) Magnetic field - 0.308 Gauss Albedo - 37% Atmosphere - 1 bar (1 atmosphere)

78.1% N2, 20.9% O2, 0.9% Ar

Mars

Mars has a small CO2 atmosphere, but a distant past that had similar characteristics to Earth including a magnetic field, liquid surface water, and active volcanoes

A thick crust and solidification of the interior of the planet halted most of its geological activity after the first billion years as a planet

Mars does contain permanent polar ice caps of water and CO2 ice and subsurface ice discovered on recent exploration missions

Mars

Mass - 6.421x1023 kg (0.11 MEarth) Radius - 3,397km (equatorial) (0.53

REarth) Mean density - 3.93 g/cm3

Semimajor axis - 1.52 AU Orbit period - 1.88 yr Rotation period - 24.62 hr Magnetic field - No dipolar field, but

weak, localized magnetization of the iron-rich crust

Albedo - 15% Atmosphere - 0.007 bar 95.2% CO2,

2.7% N2, 1.6% Ar

Jovian Planets

Jovian Planets

Jovian planets are the giant gas and ice planets formed beyond the terrestrial region

A number of common features exist in the Jovian planets, including:

Large mass

Innermost rock and metal core

Outer envelope of hydrogen and helium gas

Rapid rotation

Strong magnetic fields

Jovian Planets

Jovian planets began as large ice and rock (planetesimal) cores

Large, dense gas regions accelerated the process

These cores were large planets in themselves, and could attract ice and gas unavailable to the terrestrial planets This allowed them to rapidly gain mass because

there was more gas and ices in their neighborhood

Jovian Planets

Jovian Planets

A comparison of the interiors of the Jovian planets shows a distinct difference between the two largest, Jupiter and Saturn, and the two smallest, Uranus and Neptune

The largest two, Jupiter and Saturn, are called giant gas planets because of their principal gas composition, although little is actually in the gas state

The two smallest are the giant ice planets Uranus and Neptune Both Uranus and Neptune do contain a significant hydrogen

and helium atmosphere, but they are dominated by ices in liquid form

The term "ice planet” should not be confused with the dwarf ice bodies and planets similar to Pluto, its moon Charon, and a host of other comet-like planets much smaller These have a distinctly different composition than Uranus

and Neptune

Jovian Planets

Jupiter

Jovian Planets

Jupiter

One of the brightest planets in the night sky because of its tremendous size (11 x REarth) and light-colored upper cloud layers (high albedo) (high albedo)

First to observe and document Jupiter's features and four nearby moons was Galileo, for which the four Galilean moons are named

Rapid rotation (9.93 hr) and high Rapid rotation (9.93 hr) and high mass (318 x Mmass (318 x MEarth) generates a huge ) generates a huge magnetic fieldmagnetic field

Jovian Planets

Jupiter

Largest magnetic field of the planets (11-14 Gauss)

Atmosphere – 90% H, 10% He

Interior composed of liquid H, He, and H compounds

Deep interior included hydrogen under tremendous pressure and temperature that forces the atoms into a degenerate state – metallic hydrogen

Jovian Planets

Jupiter

Metallic hydrogen mantle is superconducting which is thought to circulate magnetodynamo currents to flow without resistance and generate Jupiter’s enormous magnetic field Stretches beyond the orbit of Saturn 5 AU away

OrbitOrbit 11.86 yr11.86 yr 5.2 AU5.2 AU

Rotation period – 9.925 hr (fastest of all planets)Rotation period – 9.925 hr (fastest of all planets)

Jovian Planets

Jupiter

Mass – 318 x MEarth

Albedo (reflectance) – 52%Albedo (reflectance) – 52%

Moons – 63 (as of 2007)Moons – 63 (as of 2007)

Exploration spacecraftExploration spacecraft Pioneer 10Pioneer 10 Pioneer 11Pioneer 11 Voyager IVoyager I Voyager IIVoyager II Ulysses (gravity assist to Sun’s Ulysses (gravity assist to Sun’s

poles)poles) New Horizons (gravity assist to New Horizons (gravity assist to

Pluto)Pluto) Galileo (dedicated orbiter)Galileo (dedicated orbiter)

Jovian Planets

Jupiter

Four largest moons called the Galilean moons (named after Galileo Galilei) who discovered the moons

Io Closest, and undergoes

highest tidal forces Tidal flexing heats the

interior to a molten state and generates the most geologically active celestial body in the solar system

Jovian Planets

Europa

Next moon out is covered with an icy crust that overlays a liquid water interior

Conditions may be sufficient to support primitive life

Weak magnetic field measured by the Galileo spacecraft

Indicative of conductive water ocean beneath icy surface

Two possible structures shown on the right

Jovian Planets

Ganymede Largest moon in the solar system Weak magnetic field may be made possible by a conductive Weak magnetic field may be made possible by a conductive

water layer beneath the icy crustwater layer beneath the icy crust

Callisto 3rd largest moon in the solar system Interior 40% ice and 60% rock/metal Also has a conductive water ocean below the icy surface that

influences Jupiter’s magnetic field

Jovian Planets

Saturn

Jovian Planets

Saturn

Second largest planet in the solar system

Lowest density planet in the solar system (0.69 g/cm3, water is 1.00 g/cm3)

Rapid rotation (10.78 hr) and high mass (95x MRapid rotation (10.78 hr) and high mass (95x MEarth) ) generates a large magnetic field, but significantly generates a large magnetic field, but significantly smaller than Jupiter’ssmaller than Jupiter’s


Jovian Planets

Saturn

Allbedo – 47%

Also contains a metallic hydrogen mantle


Largest ring system of the planets

Exploration spacecraft Pioneer 11 Voyager I Voyager II Cassini (dedicated orbiter)

Jovian Planets

Saturn Hydrogen and helium atmosphere

with trace amounts of methane, water, ammonia, and hydrogen sulfide

Most prominent feature is its ring system Extends approximately 67,000 Extends approximately 67,000

km to 480,000 kmkm to 480,000 km Saturn's rings composed Saturn's rings composed

primarily of small ice particles primarily of small ice particles that have been chargedthat have been charged

Allows the orientation and Allows the orientation and position of the particles to position of the particles to change slightly when the change slightly when the Saturnian magnetic field passes Saturnian magnetic field passes throughthrough

Saturn and its rings in UV

Saturn’s rings

Saturn’s surroundings

Saturn

Titan

Saturn’s largest moon is Titan Larger than both Pluto and Mercury Larger than both Pluto and Mercury

Only moon with a significant atmosphere Only moon with a significant atmosphere found in the solar systemfound in the solar system

Similar to several of Jupiter's moons Rocky core overlayed with a mantle

composed of water and ammonia ice layers

Roughly 2/3 of the moon is Roughly 2/3 of the moon is rock/silicate/metal that remains warm, or rock/silicate/metal that remains warm, or perhaps hotperhaps hot Likely creates conditions for a liquid Likely creates conditions for a liquid

water layer in the upper ice mantlewater layer in the upper ice mantle

Saturn

Titan

High atmospheric pressure (1.5 x Earth’s) and cold temperature (94 K, -290oF) creates a triple-point environment for methane and ethane on Titan’s surface Solid, liquid, and gas, like

water on Earth

Ammonia’s low abundance Ammonia’s low abundance and variable concentration is and variable concentration is also like water in Earth’s also like water in Earth’s atmosphereatmosphere

Saturn

Titan

Rain composed of ethane and Rain composed of ethane and methane erode Titan’s surface methane erode Titan’s surface which form large lakeswhich form large lakes Located near poles because

of seasons Identified by imaging radar

on Cassini (see image on right)

Lakes are small in comparison Lakes are small in comparison to Earth’sto Earth’s

Saturn

Titan Alcohol and ammonia rains create river

channels and broad, flat basins that appear to be ocean beds

Methane is not stable and not retained on Methane is not stable and not retained on TitanTitan Must be replenished, probably from Must be replenished, probably from

porous sands in “ocean” bedsporous sands in “ocean” beds

Small, cold volcanoes (cryovolcanoes) Small, cold volcanoes (cryovolcanoes) possible source of methane & ethanepossible source of methane & ethane

Thick haze that prevents direct Thick haze that prevents direct observation is due to solar energy observation is due to solar energy producing hydrocarbons from ethane producing hydrocarbons from ethane and methaneand methane

Saturn

Titan Images of Titan’s surface show

rocks littering flat plateau at the landing site

Origin of rocks likely from Origin of rocks likely from cryovolcanoes releasing liquid cryovolcanoes releasing liquid water that freeze into hard clumps water that freeze into hard clumps that persist for a very long timethat persist for a very long time Water ice is too cold to sublimate Water ice is too cold to sublimate

at 94 Kat 94 K

Liquid water interior also Liquid water interior also responsible for a different rotation responsible for a different rotation of its crust compared to its of its crust compared to its interior (measured accurately interior (measured accurately during Cassini flybys)during Cassini flybys)

Close similarity between Titan’s Close similarity between Titan’s and Earth’s geology and and Earth’s geology and atmosphereatmosphere

Saturn

Enceladus

Smaller and more distant than Titan is Enceladus which has a tortured, icy outer surface

Located in the dense region Located in the dense region of the Saturn's diffuse outer of the Saturn's diffuse outer E-ringE-ring

Two different surface Two different surface characteristics in northern characteristics in northern and southern hemispheresand southern hemispheres Sparsely-cratered Sparsely-cratered

northern region northern region Young, uncratered Young, uncratered

southerly zonesoutherly zone

Saturn

Enceladus

Tidal heating of the interior by Tidal heating of the interior by Saturn generates liquid Saturn generates liquid cryovolcanoes near the south cryovolcanoes near the south polar region which spew frozen polar region which spew frozen particles into Saturn’s E-ringparticles into Saturn’s E-ring

Light-colored surface indicative Light-colored surface indicative of active ice formation (celestial of active ice formation (celestial snow)snow)

Water ice from Enceladus Water ice from Enceladus contributes significantly to contributes significantly to Saturn’s E-ringSaturn’s E-ring

Saturn

Enceladus

Tidal heating by Saturn Tidal heating by Saturn generates continual generates continual cryovolcanismcryovolcanism

Discovered during Cassini Discovered during Cassini flybys with backlighting from flybys with backlighting from the Sunthe Sun

Source of tidal heating?

Tidal flexing requires slightly Tidal flexing requires slightly elliptical orbit, but tides elliptical orbit, but tides gradually reduce eccentricity gradually reduce eccentricity (Enceladus’ orbit should be (Enceladus’ orbit should be circular by now)circular by now)

Enceladus’ eccentric orbit due Enceladus’ eccentric orbit due to perturbation from 2:1 orbital to perturbation from 2:1 orbital resonance with Saturn’s moon resonance with Saturn’s moon DioneDione

Jovian Planets

Uranus

Jovian Planets

Uranus

One of two Jovian giant ice planets

Discovered in 1781 by William Herschel First planet discovered by

a telescope Previous discoveries were

of large asteroids (minor planets Ceres and Vesta were the two largest)

Rotational axis is offset 98o from the normal

Jovian Planets

Uranus

Structural model consists of three layers

Rocky core Small in comparison to giant gas planets

Ice mantle Contains the majority of the mass Consists of water, ammonia and other

volatiles in liquid form

Outer gaseous hydrogen/helium envelope is a dull green-blue due to methane

Jovian Planets

Uranus

Mass – 14.5 MMass – 14.5 MEarthEarth


Moons – 27 (as of 2007)Moons – 27 (as of 2007) Aligned with equator (nearly Aligned with equator (nearly

vertical)vertical)

Exploration spacecraftExploration spacecraft Voyager IIVoyager II

Jovian Planets

Uranus

Small ring system Small ring system discovered in Voyager II discovered in Voyager II datadata

False-color image from False-color image from Voyager on the right Voyager on the right shows circulation bands shows circulation bands and the storm regions and the storm regions near the polar bandnear the polar band

Jovian Planets

Miranda

One of the most unusual moons in One of the most unusual moons in the solar system is Uranus’ moon the solar system is Uranus’ moon MirandaMiranda

Chaotic features include deep, Chaotic features include deep, long canyons 10 times deeper than long canyons 10 times deeper than the Grand Canyonthe Grand Canyon

Violent collision between moon Violent collision between moon during Uranus catastrophic during Uranus catastrophic formation likely broke up the formation likely broke up the original moon and reformed it with original moon and reformed it with jumbled surface featuresjumbled surface features

Jovian Planets

Neptune

Jovian Planets

Neptune

The largest Jovian ice planet

Discovered 1846 by French astronomer Urbain Le Verrier

Similar to Uranus, the structural model consists of three layers Rocky core Ice mantleIce mantle Outer gaseous Outer gaseous

hydrogen/helium envelopehydrogen/helium envelope

Jovian Planets

Neptune

Mass – 17.2 MMass – 17.2 MEarthEarth



Small ring system discovered Small ring system discovered in Voyager II datain Voyager II data

Exploration spacecraftExploration spacecraft Voyager IIVoyager II

Jovian Planets

Neptune

Lowest temperatures in upper atmosphere of all the planets Highest wind speeds

measured at approx. 1,500 mph

Circulation bands are visible, Circulation bands are visible, along with giant dark spot along with giant dark spot similar to Jupiter’s and high-similar to Jupiter’s and high-altitude clouds travelling at altitude clouds travelling at extremely high speedsextremely high speeds

Neptune

Triton

Neptune’s largest moon is Triton

Triton’s diameter is 78% of the Earth's moon, but only 28% of its mass Density 2.05 g/cm3 (lunar

density is 2.05 g/cm3

Surface shows complex features with few craters which indicates a relatively young surface

Neptune

Triton

Cryovolcanoes of Cryovolcanoes of liquid nitrogen from liquid nitrogen from beneath the ice crust beneath the ice crust indicate tidal heating indicate tidal heating and subsurface liquid and subsurface liquid nitrogen and possibly nitrogen and possibly water oceanswater oceans

Spectral imaging data Spectral imaging data shows Triton's shows Triton's surface covered with surface covered with nitrogen ice, water nitrogen ice, water ice, carbon dioxide ice, carbon dioxide ice, methane ice, and ice, methane ice, and ammonia iceammonia ice

Trans-Neptunian Objects

Beyond Neptune

Trans-Neptunian objects are small icy bodies scattered by the massive planet Neptune which itself was scattered outward by Jupiter in its early history

Pluto

Pluto, the most distant of the original nine planets has the largest moon-planet mass ratio in the solar system

Discovered in 1930 by Clyde Tombaugh

Pluto’s largest moon Charon was discovered in 1978 The large mass of

Charon compared to Pluto makes them more of a binary pair than a planet-moon system (both orbit around a center of mass outside Pluto’s surface)

Pluto

Pluto’s two other moons Nix and Hydra are 2 and 3 times the distance of Charon from Pluto, but much smaller (also orbit around the Pluto-Charon barycenter)

Exploration spacecraft New Horizons (2006

launch for a July 2015 flyby)

Pluto

Mass 1.305×1022 kg (0.2% MEarth) Radius 1,195 km Mean density 2.03 g/cm3

Orbital eccentricity 0.24881 Orbit inclination 17.142o

Semimajor axis 39.48 AU (5.91x109 km)

Orbit period 248.09 yr Rotation period 6d 9h 17m 36s

Rotational axis tilt 119.59o

Magnetic field Unknown Albedo 0.49–0.66 Atmosphere nitrogen,

methane, and carbon monoxide (surface ice sublimation)

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