Announcements the OUTER PLANETS

11/17/16

Announcements

! Tonight’s observing session is on! ! The 8th LearningCurve activity was due earlier today ! Assignment 8 and Quiz 8 will be due on Tue. Nov. 22

THE OUTER PLANETS

! This section deals with the 4 planets whose orbits lie outside those of the terrestrial planets ! These outer planets are called gas giant planets ! Jupiter, Saturn, Uranus, and Neptune ! Pluto is much smaller, and is no longer classiﬁed as a regular planet

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Exploration of the Outer Planets

! Pioneer 10 was launched in March 1972 ! In Dec. 1973, it became the ﬁrst spacecraft to pass close to Jupiter ! It came within 130,000 km of Jupiter’s cloud-tops, and returned the ﬁrst ever close-up images

Pioneer 11

! Pioneer 11 left Earth in April 1973 ! It passed close to Jupiter in Dec. 1974 ! It later ﬂew to within 20,000 km of Saturn in Sept. 1979 ! Pioneer 11 returned the ﬁrst close-up pictures of Saturn

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Voyager 1 and 2

! NASA’s Voyager 1 spacecraft ﬂew by Jupiter in 1979, and Saturn in 1980 ! Voyager 2 ﬂew by: ! Jupiter in 1979 ! Saturn in 1981 ! Uranus in 1986 ! Neptune in 1989 ! To this date, no other spacecraft has visited Uranus or Neptune

The Paths of Voyager 1 and 2

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The Galileo Orbiter and Probe

! The Galileo spacecraft arrived at Jupiter on Dec. 7, 1995, after a 6-year trip ! Upon arrival, it also released a small probe, which parachuted into Jupiter’s atmosphere ! Galileo was crashed into Jupiter in 2003

The Cassini Mission to Saturn

! NASA’s Cassini spacecraft arrived at Saturn in July 2004 ! it remains in orbit around Saturn, and continues to make ﬂybys of its moons ! It sent a probe (Huygens) to the surface of Titan in January 2005

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The JUNO Mission to Jupiter

! NASA’s JUNO spacecraft arrived in orbit around Jupiter on July 4, 2016

! It will study the atmosphere and interior of Jupiter 9

Recent Images From JUNO

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Jupiter

! Jupiter is the ﬁfth planet from the Sun ! its average distance from the Sun is 5.2 AU ! It takes about 12 years to orbit the Sun ! Jupiter rotates once every 10 hours ! this is the fastest of all the planets

Jupiter’s Size and Mass

! Jupiter is the solar system’s largest planet ! its diameter is ~11 times larger than Earth’s ! if it were hollow, 1300 Earths could ﬁt inside it! ! It is also the most massive planet ! this means it contains the most mass ! it is 318 times more massive than the Earth ! it is more than twice as massive as all of the other planets combined!

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Jupiter’s Cloud Layer

! Jupiter is always covered in clouds, which lie in a layer that is 50 km thick ! These clouds are made primarily of sulphur, water, and ammonia compounds

Jupiter’s Great Red Spot

! Many features are seen in the cloud layer ! Atmospheric bands encircle the planet ! Many storm systems are seen ! The largest – called the Great Red Spot – has been around since at least 1665!

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Close Up of the Great Red Spot

Jupiter’s Atmosphere

! Below the clouds, there is a 20,000 km thick layer of hydrogen and helium ! this layer gradually changes from gas to liquid as the depth (and pressure) increases

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Jupiter’s Interior

! Below the liquid hydrogen is a 40,000-km thick sea of liquid metallic hydrogen ! this dense material is probably responsible for Jupiter’s powerful magnetic ﬁeld ! In the centre there is an even denser core of iron, rock and water ! it is unclear if this layer is solid or not ! even if solid, the atmospheric pressure would be far too great for a person to stand or walk

Jupiter’s Moons

! Jupiter has at least 67 moons Io Europa (more than 1/3 of the 173 known solar system moons) ! this total is for the moons of the 8 modern day planets Amalthea ! Galileo discovered the four largest moons in 1610 ! they are known as the Galilean moons ! The remaining 63 known moons are much smaller

Ganymede Callisto 18

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Ganymede

! Ganymede is the largest moon in the solar system ! it is also larger than Mercury and Pluto ! its diameter is 5200 km ! It has frosty polar ice caps and a thin atmosphere ! It has an iron-rich core, a rocky mantle, an ice/water layer, and a surface of dirty ice

The Interior of Ganymede

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The Surface of Ganymede 110 km ! The icy surface of Ganymede has many impact craters ! this implies that its surface is very old ! It is also crisscrossed by grooves and ridges ! these unusual features appear to be tectonic in nature

Callisto

! Callisto is Jupiter’s second largest moon ! It is the outermost of the Galilean moons ! It takes about 17 days to orbit Jupiter ! Its icy surface is mostly covered by dark dust from meteorites

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Callisto’s Impact Basins & Craters

Callisto’s Interior

! Callisto’s core is composed mainly of rock and ice ! The crust is 200 km thick and is made mostly of ice ! There may be a thin ocean of salt water in between

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Europa

! Europa is the smallest Galilean moon ! Its icy surface is very smooth and few craters are seen ! This implies that its surface is very young ! the oldest regions are only about 10 million years old

The Surface of Europa

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Sea Salt on Europa?

A recent study indicates that the red linear features on the surface of Europa are consistent with sea salts which have been exposed to radiation. 27

HST Evidence of Water Vapo ur Vents

! Recent images and spectra from the Hubble Space Telescope (HST) appear to have detected water vapour vents near Europa’s south pole ! These are thought to have been emitted from cracks on Europa’s surface 28

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The Interior of Europa

How Much Water is in Europa’s Oceans?

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A Salt Water Ocean on Europa?

! The water layer may contain an ocean of salt water ! this layer contains more water than all of the Earth’s oceans combined ! It is possible that life exists within this ocean!

! The innermost of the Galilean moons is named Io ! It is one of the most unusual moons in the solar system ! Its surface is rich in sulphur, giving it distinctive colours ! Io has no impact craters!

A true-colour image of Io 32

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Volcanism on Io

! In 1979, the Voyager spacecraft observed 9 different volcanoes erupting! ! Io is the only place (besides Earth) where active volcanoes have been seen ! The volcanism on Io is due to tidal stresses from Jupiter, Europa and Ganymede

Io’s “Ra Patera” Shield Volcano

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RecentA eruptionRecent (Nov. Eruption1999) on Io

Active eruption (Feb. 2000)

250 km 35

The Effects of Volcanism on Io

! Erupting volcanoes blast sulfurous gas and ash over the surface of Io, wiping out any newly formed craters ! Despite ongoing volcanism, Io’s surface is mostly very cold (about -143° C), so some sulphur dioxide frost can be seen ! however, no water or ice is present on Io ! It is estimated that volcanism completely resurfaces Io every million years or so

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Jupiter’s Smaller Moons

! Jupiter has at least 63 small moons ! The largest of these is only 250 km across ! All of these small moons were probably captured after Jupiter and its Galilean moons had formed

Amalthea Thebe Metis Galileo Images:

Jupiter’s Rings

! Jupiter also has a very faint system of rings ! These rings are made of tiny particles of rock dust that are orbiting around Jupiter ! This dust probably originates from meteoroid impacts on Jupiter’s tiny inner moons

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Schematic of Jupiter’s Rings

Saturn

! Saturn is the second largest planet in the solar system ! At 9.5 AU, it is nearly twice as far out as Jupiter, and orbits the Sun every 30 years ! Its rotation period is about 11 hours ! Saturn is best known for its distinctive rings

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Saturn’s Atmosphere

Saturn’s atmosphere is similar to Jupiter’s, with numerous storms. 41

A Storm on Saturn in 2011

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Lightning on Saturn!

Saturn’s Polar Vortex

This near-infrared image from Cassini shows the six-sided jet stream surrounding a 2000-km wide red hurricane-like system at the north pole. 44

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Saturn’s Interior

! Saturn’s interior is similar to Jupiter’s, though less dense ! Its rocky core is about 32,000 km in diameter ! Saturn also has a strong magnetic ﬁeld ! This is produced by its layer of liquid metallic hydrogen 45

Persistant Aurorae on Saturn

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Saturn Eclipses the Sun

The Makeup of Saturn’s Rings

! Saturn’s rings are not solid, but instead are made up of numerous small particles ! most are the size of dust particles up to a few cm in size ! These particles are made of ice and rock ! These particles all orbit Saturn under the inﬂuence of its gravitational attraction ! the inner particles orbit the fastest ! in fact, all of the particles obey Kepler’s Laws ! Saturn’s main ring system is about 380,000 km wide but only about 10 m thick!

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Saturn’s Rings as seen by Cassini

Cassini’s View of Saturn’s Rings

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Gaps in Saturn’s Rings

! Many divisions are seen in the ring system ! in fact, there are thousands of distinct ringlets! ! Some gaps in the rings are due to resonances with Saturn’s larger moons ! at some distances from Saturn, ring particles cannot stay for long, so these regions are relatively empty ! Other spaces between rings are kept clear by tiny moons which orbit within the rings

Moons within Saturn’s Rings

Encke gap F Ring

Pandora

Prometheus

Pan

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The Orientation of Saturn’s Rings

! Saturn’s appearance depends on the orientation of its rings with respect to us ! When its rings are aligned with Earth, they are hard to see ! At any other time, they are hard to miss!

Saturn Seen From Above (by Cassini)

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Saturn Seen Edge-on by Cassini

How Did Saturn’s Rings Form?

! Saturn’s ring system may have formed when a Titan-sized moon was accreted by Saturn early in its history ! This moon would have migrated inward within a disk of gas that orbited Saturn ! The icy outer layers would have been stripped off before this moon fell into Saturn ! Some of this icy material remains in orbit around Saturn, making up its main ring system

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Saturn’s Moons

! Saturn has at least 62 moons ! many of these moons were discovered by Cassini ! Most of Saturn’s moons are very small and non- spherical ! they are probably captured asteroids ! Saturn’s largest moon is named Titan Prometheus

Saturn’s Moon Titan

! Titan is the second largest moon in the solar system ! only Ganymede is larger ! It is surrounded by a thick, opaque atmosphere ! this prevents us from seeing the surface in visible light ! the atmosphere is made mainly of nitrogen and methane ! Titan is the only moon in the solar system that has a thick atmosphere

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Titan’s Haze

Multiple Layers of Haze on Titan

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The Surface of Titan

Before the Huygens probe arrived at Titan, there had been speculation that the surface of Titan might have:

! huge mountains of ice (made of frozen water or methane) ! hydrocarbon oceans and lakes ! a smoggy sky and gasoline rain

Cassini false-colour image 61

Descent to the Surface of Titan

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Dry Riverbeds on Titan?

Huygen’s Landing Site

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Scientiﬁc Results From Cassini and Huygens

! Smog particles appear to precipitate out of the atmosphere, falling as dark “dust” ! Methane “rain” appears to fall occasionally, and this washes the dust down from the mountains ! There are clear signs of dry riverbeds and lakebeds (with bottoms coated in dust) ! Methane lakes have been found at northern latitudes

Hydrocarbon Lakes on Titan

! Cassini has found hundreds of lakes on Titan ! these lakes are found only in Titan’s polar regions ! Analysis indicates that these lakes are made of: ! 75-80% ethane ! 7-8% propane ! 5-10% methane ! 5% other compounds

Source: Cordier et al. (2009)

Cassini radar map of lakes on Titan66

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Polar View of Titan’s Lakes

Sunlight Reﬂecting Off a Methane Lake on Titan

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A Transient Feature in a Lake on Titan

! A 20-km long object appeared and later disappeared in a lake on Titan

! This could be due to ﬂoating ice, bubbles or waves 69

Methane Rain on Titan

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Future Exploration of Titan?

Saturn’s Moon Enceladus

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Ice Plumes on Enceladus

Cassini image from Nov. 2009 73

An Ice Volcano on Enceladus

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Tiger Stripes on Enceladus

Tiger Stripes

! Thermal measurements from Cassini show that tiger stripes can be much warmer than their surroundings ! some are as warm as -80 Celsius ! this is indicative of volcanic activity, which would be warm enough to melt some of the subsurface ice

Cassini tiger stripe close-up 76

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Opening and Closing of Tiger Stripes

! The elliptical orbit of Enceladus around Saturn creates higher tidal stress when Enceladus is closest to Saturn ! High tidal stress compresses Enceladus and causes the tiger stripes to mostly close up ! Cassini measurements indicate that plume activity is four times higher at apocentre than at pericentre

An Ocean Below the Crust of Enceladus

Analysis of the plume and detailed gravitational measurements indicate that there is a salty ocean below the surface of Enceladus. 78

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Uranus

! Uranus is nearly twice as far from the Sun as Saturn, at 19 AU ! Despite being much larger than the inner planets, it is too faint to see with the naked eye ! It was discovered by William Herschel in 1781

The Size of Uranus

! Uranus has a diameter of about 50,000 km ! this is equal to about 4 Earth diameters ! It is barely larger than Neptune, but less massive

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The Rotation of Uranus

! The rotation axis of Uranus is tilted by about 98° ! this may be the result of a major collision with an Earth-sized object at some time in the past ! As a result, Uranus has the most extreme seasons of any of the planets

The Extreme Seasons of Uranus

Note: a Uranus year is 84 Earth years long. 82

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The Moons of Uranus

! Uranus has at least 27 moons ! only 5 moons were known before 1986 ! Voyager 2 identiﬁed 10 new moons ! The largest – Titania – is less than half of the diameter of our Moon

Titania (1580 km across) 83

The OberonMoons of Uranus Titania

Umbriel

Miranda

Puck (150 km across)

Ariel 84

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The Rings of Uranus

! In 1977, 5 rings were found around Uranus ! they were detected when Uranus passed in front of a distant star ! Voyager 2 imaged these narrow rings, and found 5 others ! Some of the rings have shepherd moons

The Rings of Uranus Seen Edge-on

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The Atmosphere of Uranus

! Uranus is surrounded by an atmosphere of mostly hydrogen ! It also has some high altitude methane, which give it its bluish colour ! Uranus is almost featureless in visible light, but does have clouds and bands

Neptune

! The planet Neptune was discovered by Johann Galle in 1846 ! Its existence had been predicted, due to its gravitational inﬂuence on Uranus ! It is very much like Uranus in terms of size and overall makeup

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Neptune’s Orbit and Rotation

! Neptune lies at a distance of 30 AU ! Its orbital period (year) is 165 years ! It rotates once every 19 hours ! Its rotation axis is tilted by about 30°

Neptune’s Great Dark Spot

! Neptune’s atmosphere is similar to that of Uranus ! Voyager 2 discovered a large storm in 1989 ! this Neptunian storm was named the Great Dark Spot ! This cloud pattern was as large as the Earth! ! This storm has since dissipated, but other storms have been seen

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Neptune’s Moons

! Neptune has 14 known moons ! 13 of these are very small and irregular ! The other, named Triton, is much larger ! Triton is spherical and a bit larger than Pluto ! Triton has an retrograde orbit around Neptune, which will cause it to spiral inwards and be torn apart by tidal stresses

Neptune’s Rings

! Like the other gas giant planets, Neptune has rings too ! It has two main rings, which are very faint ! Voyager 2 ﬁrst veriﬁed their existence in 1989 ! These rings may be replenished by comets crashing into Neptune’s inner moons

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The Interiors of Uranus and Neptune

! Both Uranus and Neptune appear to have: ! a rocky core ! a liquid water mantle ! a surrounding layer of liquid hydrogen and helium

Before Next Class

! Complete Assignment 8 and Quiz 8 ! due on Tue. Nov. 22 at 2 p.m. ! Read Chapter 9 ! Complete LearningCurve: Vagabonds of the Solar System ! due on Thu. Nov. 24 at noon