Homework #4  Due today, 11:59PM  Covers Chapters 6 and 7  Estimated time to complete: 1 hour  Read chapters, review notes before starting  Due today, 11:59PM  Covers Chapters 6 and 7  Estimated time to complete: 1 hour  Read chapters, review notes before starting

Homework #5  Due Thursday, March 3, 11:59PM (Exam #2 will be the following day)  Covers Chapters 8, 9, and 10  Estimated time to complete: 1 hour  Read chapters, review notes before starting  Due Thursday, March 3, 11:59PM (Exam #2 will be the following day)  Covers Chapters 8, 9, and 10  Estimated time to complete: 1 hour  Read chapters, review notes before starting

Midterm Grades  Midterm grades will be posted tonight  Homework #4 will not be included in your midterm grade  Be sure to do Homeworks #1, #2, #3 for partial credit if you have not completed them  If you did not take Exam #1, your midterm grade won’t be based on much!  Midterm grades will be posted tonight  Homework #4 will not be included in your midterm grade  Be sure to do Homeworks #1, #2, #3 for partial credit if you have not completed them  If you did not take Exam #1, your midterm grade won’t be based on much!

What makes a planet habitable?  Large enough for geological activity to release gas and retain water and atmosphere (size is most important factor)

What makes a planet habitable?  Located at an optimal distance from the Sun for liquid water to exist (location, location, location)

Earth’s Destiny Earth is habitable because it is large enough to remain geologically active, and it is at the right distance from the Sun so liquid water survive on the surface.

Chapter 7 Study Guide 1)Terrestrial planets have radically different geologies, atmospheres despite common origin inside frost line 2) Core (high density iron/nickel)  mantle (moderate density silicate rocks)  crust (low density rocks) 3) When planets were still molten, denser material sunk to the center  called differentiation 4) Lithosphere – crust + outer part of mantle – cool rigid rock that floats on top of soft, warm rock of inner part of mantle 5) A planet’s internal heat determines level of geological activity

Chapter 7 Study Guide 6) Early times: differentiation + accretion  heat Now: radioactive decay in core  heat 7) Size is most important factor in determining how long a planet’s interior stays hot; when heat is gone, geological activity is gone, rock hardens, atmosphere goes away 8) Impact cratering, volcanism, tectonics, erosion all shape the surfaces of worlds 9) During volcanic eruptions, copious amount of gas is released  outgassing  replenishes gas in atmospheres 10) Earth’s atmosphere creates erosion, protects from radiation, responsible for greenhouse effect, makes sky blue

Chapter 7 Study Guide 11) Greenhouse gases (CO 2, H 2 O, CH 4 ) trap in infrared photons emitted by blackbody Earth  make surface warmer 12) Moon and Mercury had geological activity (~3 billion years ago) – maria on Moon – but not any longer (too small, lost internal heat) – no atmospheres because no more outgassing 13) Mars – thin atmosphere, recent geological activity which is probably dying down now, good evidence for much liquid water in past (know the evidence)  probably lost much of internal heat because of moderate/small size 14) Venus – extremely thick atmosphere, very recent geological activity, greenhouse effect run wild 15) Earth – broken lithosphere allows plates to drift  continents move slowly

Chapter 7 Study Guide 16) Continental motion – caused by spreading of sea floor  hot rock pushes up from mantle pushing plates apart 17) CO 2 cycle keeps CO 2 levels stable  good for climate stability 18) Fossil fuel burning is raising CO 2 levels to unprecedented levels  can Earth’s CO 2 cycle compensate? 19) A planet’s chance to harbor life depends on its distance from the Sun (not too hot, not too cold) and size (large enough to maintain internal heat for geological activity)  Lucky Earth!

Chapter 8 Jovian Planet Systems

Jovian Planet Composition  Jupiter and Saturn - mostly H and He gas, with small amounts of hydrogen compounds (ices), rock, and metal  Uranus and Neptune - majority hydrogen compounds: water (H 2 O), methane (CH 4 ), ammonia (NH 3 ), some H, He, and rock/metal (better named “ice giants”)  Jupiter and Saturn - mostly H and He gas, with small amounts of hydrogen compounds (ices), rock, and metal  Uranus and Neptune - majority hydrogen compounds: water (H 2 O), methane (CH 4 ), ammonia (NH 3 ), some H, He, and rock/metal (better named “ice giants”)

Jovian Planet Formation  Beyond the frost line, planetesimals could accumulate ICES (hydrogen compounds) in addition to rock/metal (these ices were not available in the inner Solar System where the terrestrials formed due to high temperatures).  Hydrogen compounds were more abundant than rock/metal so proto-Jovian planets got more massive and acquired H/He atmospheres.  Beyond the frost line, planetesimals could accumulate ICES (hydrogen compounds) in addition to rock/metal (these ices were not available in the inner Solar System where the terrestrials formed due to high temperatures).  Hydrogen compounds were more abundant than rock/metal so proto-Jovian planets got more massive and acquired H/He atmospheres.

Comparing Jovian Interiors  Models suggest cores of Jovian planets are made of similar materials, but different layer ratios.  More H/He in Jupiter/Saturn, more ices in Uranus/Neptune (by percentage)  Models suggest cores of Jovian planets are made of similar materials, but different layer ratios.  More H/He in Jupiter/Saturn, more ices in Uranus/Neptune (by percentage)

Jovian Planet Formation  No solid surface  Layers under high pressure and temperatures  The Jovian cores are all very similar: mass of ~5-10 Earths (made of ices/rock/metal)  The Jovian planets differ in the amount of H/He gas accumulated. Why did that amount differ?  No solid surface  Layers under high pressure and temperatures  The Jovian cores are all very similar: mass of ~5-10 Earths (made of ices/rock/metal)  The Jovian planets differ in the amount of H/He gas accumulated. Why did that amount differ?

Differences in Jovian Planet Formation  TIMING: The planet that forms earliest captures the most hydrogen and helium gas. Capture ceases after the solar wind blows the leftover gas away.  LOCATION: The planet that forms in a denser part of the nebula forms its core first  favors Jupiter, then Saturn, but disfavors Uranus, Neptune  TIMING: The planet that forms earliest captures the most hydrogen and helium gas. Capture ceases after the solar wind blows the leftover gas away.  LOCATION: The planet that forms in a denser part of the nebula forms its core first  favors Jupiter, then Saturn, but disfavors Uranus, Neptune

Inside Jupiter  Core is thought to be made of rock, metals, and hydrogen compounds.  Core is about same size as Earth but 5-10 times as massive.  Tremendous pressure within inner layers leads to extremely high temperatures About same temperature as surface of Sun!

Inside Jupiter  High pressures inside Jupiter cause phase of hydrogen to change with depth.  Hydrogen acts like a metal at great depths because its electrons move freely (metallic hydrogen).

What is the weather like on Jovian planets?

Jupiter’s Colors  Ammonium hydrosulfide clouds (NH 4 SH) reflect red/brown.  Ammonia, the highest, coldest layer, reflects yellowish-white.  Ammonium hydrosulfide clouds (NH 4 SH) reflect red/brown.  Ammonia, the highest, coldest layer, reflects yellowish-white.

Jupiter’s Atmosphere  Hydrogen compounds in Jupiter form clouds (H/He are colorless).  Different cloud layers correspond to freezing points of different hydrogen compounds. ammonium hydrosulfide

Saturn’s Colors  Saturn’s layers are similar, but sunlight is reflected at a deeper depth. More absorption of light on the way back out leads to more subdued colors.

Methane on Uranus and Neptune  Methane gas (20x more abundant by percentage than on Jupiter/Saturn) of Neptune and Uranus absorbs red light but transmits blue light.  Blue light reflects off methane clouds, making those planets look blue.

Jupiter’s Great Red Spot  Is a storm twice as wide as Earth  Has existed for at least three centuries  Why does storm last so long? Unknown!  Is a storm twice as wide as Earth  Has existed for at least three centuries  Why does storm last so long? Unknown!

Weather on Jovian Planets  All the Jovian planets have strong winds and storms.  All the Jovian planets have strong magnetic fields (much stronger than Earth’s)  All the Jovian planets have strong winds and storms.  All the Jovian planets have strong magnetic fields (much stronger than Earth’s)

All the Jovians share the following properties except: A) A mostly H/He composition B) Strong winds and storms in their atmospheres C) Magnetic fields much greater than Earth’s D) ~5-10 Earth-mass cores of ice/rock/metal

All the Jovians share the following properties except: A) A mostly H/He composition B) Strong winds and storms in their atmospheres C) Magnetic fields much greater than Earth’s D) ~5-10 Earth-mass cores of ice/rock/metal Only Jupiter and Saturn are made mostly of H/He, Uranus and Neptune are majority hydrogen compounds, with lesser amounts of H/He.

What kinds of moons orbit the Jovian planets? Moons might be more interesting than their host planets!

Sizes of Moons  Small moons (< 300 km)  No geological activity  Medium-sized moons (300–1500 km)  Geological activity in past  Large moons (> 1500 km)  Ongoing geological activity  why not dead?!?  Small moons (< 300 km)  No geological activity  Medium-sized moons (300–1500 km)  Geological activity in past  Large moons (> 1500 km)  Ongoing geological activity  why not dead?!?

Medium and Large Moons  Enough self-gravity to be spherical  Most have substantial amounts of ice  Formed in orbit around Jovian planets (like solar nebula)  Mostly circular orbits in same direction as planet rotation (except Triton)

Small Moons  These are far more numerous than the medium and large moons.  They do not have enough gravity to be spherical: most are “potato-shaped”.

Small Moons  They are probably captured comets, so their orbits do not follow usual patterns (orbit in wrong direction, or highly elliptical orbit).

Why are Jupiter’s Galilean moons so geologically active? All large Jovian moons (except Ganymede) are smaller than Mercury, and some are smaller than Earth’s Moon. So why haven’t they lost their internal heat and become geologically dead??

Io’s Volcanic Activity  Io is the most volcanically active body in the solar system, but why?  Only Jovian moon made entirely of rock/metal (area close to young Jupiter was hot  only rock/metal survived)  Io is the most volcanically active body in the solar system, but why?  Only Jovian moon made entirely of rock/metal (area close to young Jupiter was hot  only rock/metal survived)

Io’s Volcanoes  Volcanic eruptions continue to change Io’s surface. No impact craters at all.

Io’s Volcanoes  Tupan Patera, a caldera surrounded by 1 km high cliff  Currently active and venting sulfur gas  Tupan Patera, a caldera surrounded by 1 km high cliff  Currently active and venting sulfur gas hot black lava warm red sulfur deposits

What does the lack of craters on Io tell us? A) Few comets have hit Io because it is far from the Sun. B) Io’s very thick atmosphere burns up comets before they can make an impact. C) Io’s surface must be very young. D) Io is a water world, so craters are covered by liquid water.

What does the lack of craters on Io tell us? A) Few comets have hit Io because it is far from the Sun. B) Io’s very thick atmosphere burns up comets before they can make an impact. C) Io’s surface must be very young. D) Io is a water world, so craters are covered by liquid water. Io is repaved constantly by ongoing volcanic activity  any craters are quickly erased.

Tidal Heating Io is squished and stretched as it orbits Jupiter from tidal forces (recall minor effect of Moon on Earth’s tides). Very elliptical orbit makes squishing more extreme. This extreme squishing heats the internal material and keeps it warm without radioactive decay  so not geologically dead! But why is its orbit so elliptical? Effect highly exaggerated in diagram