Xi Zhang E&MS A261 <xiz@ucsc.edu> Planetary Discovery in the era of Spacecraft Exploration Xi Zhang E&MS A261 <xiz@ucsc.edu> TA: Szilard Gyalay <sgyalay@ucsc.edu>

Today’s Outline Mid-term on next Friday Planetary Formation (Chap. 8) Surface and Interior of Terrestrial Planets (Chap. 9)

Mid-Term (1) Next Friday (Nov. 3), 10:40-11:45 am Same time, same place Materials: week 1 – next Wed (read your textbook!). See topics in your email box. Close book and close note No smartphones allowed A small calculator is allowed, but the math can be readily done without them ~50 multiple choice questions Equation sheet will be provided 3

Mid-Term (2) Bring a #2 pencil Know your Student ID Bring a PINK scantron score sheet TA and me will proctor the Exam TA will have review sessions next week 4

What properties of our solar system must a formation theory explain? Patterns of motion of the large bodies Orbit in same direction and plane Existence of two types of planets Terrestrial and jovian Existence of smaller bodies Asteroids and comets Notable exceptions to usual patterns Rotation of Uranus, Earth's Moon, etc.

Nebular Theory Collapse (initiated by supernova?) Heating, Flattening, and spinning up Condensation (Ice and rock) Accretion of planetesimals Solar Wind stripping of gas Sun ignites!

Frost Line (or Snow Line) Inside the frost line: too hot for hydrogen compounds to form ices Outside the frost line: cold enough for ices to form Question: Would the Jovian planets have formed closer to the sun or farther in the disk if the solar nebula had cooled, with a temperature half its actual value?

Asteroids and Comets Leftovers from the accretion process Rocky asteroids inside frost line Icy comets outside frost line

Heavy Bombardment Leftover planetesimals bombarded other objects in the late stages of solar system formation. Impact cratering

Origin of Earth's Water Water may have come to Earth by way of icy planetesimals. Or degassing from the interior

Moons of jovian planets Moons of jovian planets form in miniature disks.

Captured Moons These are Phobos and Deimos, respectively. Unusual moons of some planets may be captured planetesimals. Mars moons have similar compositions with the asteroids.

Story of our Moon: Giant Impact Credit: Miki Nakagima Credit: Robin Canup

Odd Rotation Giant impacts might also explain the different rotation axes of some planets.

Collapse (initiated by supernova?) Heating, Flattening, and spinning up Condensation (Ice and rock) Accretion of planetesimals Solar Wind stripping of gas Sun ignites!

Was our solar system destined to be? Formation of planets in the solar nebula seems inevitable. But details of individual planets could have been different.

What caused the orderly patterns of motion in our solar system? Solar nebula spun faster as it contracted because of conservation of angular momentum. Collisions between gas particles then caused the nebula to flatten into a disk. Why are there two major types of planets? Only rock and metals condensed inside the frost line. Rock, metals, and ices condensed outside the frost line. Larger planetesimals outside the frost line drew in H and He gas.

Where did asteroids and comets come from? They are leftover planetesimals, according to the nebular theory. How do we explain "exceptions to the rules"? Bombardment of newly formed planets by planetesimals may explain the exceptions.

Surface and Interior of Terrestrial Planets

Earth's Interior Core: highest density; nickel and iron Mantle: moderate density; silicon, oxygen, etc. Crust: lowest density; granite, basalt, etc.

Terrestrial Planet Interiors Applying what we have learned about Earth's interior to other planets tells us what their interiors are probably like.

Differentiation Gravity pulls high-density material to center. Lower-density material rises to surface. Material ends up separated by density.

Lithosphere A planet's outer layer of cool, rigid rock is called the lithosphere. It "floats" on the warmer, softer rock that lies beneath.

Earth’s Interior Structure

Strength of Rock Rock stretches when pulled slowly but breaks when pulled rapidly. The gravity of a large world pulls slowly on its rocky content, shaping the world into a sphere.

Special Topic: Seismic Waves How do we know what's inside Earth? Vibrations that travel through Earth's interior tell us what Earth is like on the inside. P waves push matter back and forth. S waves shake matter side to side

Seismic Waves P waves go through Earth's core, but S waves do not. We conclude that Earth's core must have a liquid outer layer.

Seismic Waves in Earthquakes Seismogram of the 1906 earthquake recorded in Germany An earthquake is caused by sudden movement on a sub-surface fault. The energy which is released (which was stored as strain in the rock) is converted to seismic waves which radiate from the earthquake focus. These seismic waves cause ground shaking and can be measured using seismometers. San Francisco 1906 (USGS)

Quiz What is necessary for differentiation to occur in a planet? A. It must have metal and rock in it. B. It must be a mix of materials of different density. C. Material inside must be able to flow. D. All of the above E. B and C 怨毒的告密者” 怨毒的告密者”

Causes of geological activity

Heating of Planetary Interiors Accretion and differentiation when planets were young Radioactive decay is most important heat source today.