Homework #4  Due Wednesday, February 24, 11:59PM  Covers Chapters 6 and 7  Estimated time to complete: 1 hour  Read chapters, review notes before starting  Due Wednesday, February 24, 11:59PM  Covers Chapters 6 and 7  Estimated time to complete: 1 hour  Read chapters, review notes before starting

Where did asteroids and comets come from?

Asteroids and Comets Unused leftovers from the accretion process Rocky/metal asteroids inside frost line Icy comets (with some rock/metal) outside frost line

Captured Moons Unusual moons of some planets may be captured planetesimals (such as Mars’ moons).

Summary of Solar System Formation 4) Due to temperature gradient, rock/metal condenses everywhere in Solar System, while hydrogen compounds only condense to solids (ices) beyond frost line. 5) Planets grow via accretion from dust  planetesimals  planets 6) Outer large planetesimals large enough to accrete a lot of hydrogen/helium  form mini-Solar Systems with moons. 7) Solar wind (when Sun turns ‘on’) clears out remaining hydrogen/helium gas to stop further planet growth. 8) Asteroids/comets leftover unused bits and pieces that didn’t accrete onto larger planets.

How do we explain “exceptions to the rules”? Nebular theory has to be amended to account for these exceptions.

Exceptions to the Rule 1.Venus rotates backwards on its axis – why? 1.Uranus rotates on its side – why? 1.There is water (a hydrogen compound) on Earth and Mars, a place where hydrogen compounds should not be – why? 2.Earth has a very large moon for a terrestrial planet – why? Our theory will need to account for these Solar System anomalies. 1.Venus rotates backwards on its axis – why? 1.Uranus rotates on its side – why? 1.There is water (a hydrogen compound) on Earth and Mars, a place where hydrogen compounds should not be – why? 2.Earth has a very large moon for a terrestrial planet – why? Our theory will need to account for these Solar System anomalies.

Period of Heavy Bombardment  Leftover planetesimals bombarded other objects shortly after Solar System formation (few hundred million years after formation)  many big collisions led to the exceptions to the rule  Jupiter responsible for a lot of chaos  Leftover planetesimals bombarded other objects shortly after Solar System formation (few hundred million years after formation)  many big collisions led to the exceptions to the rule  Jupiter responsible for a lot of chaos

Odd Rotation of Venus and Uranus  Giant impacts might explain the different rotation axes of Venus and Uranus – each were ”smacked” at some point during the Period of Heavy Bombardment

Origin of Earth’s Water  Water may have come to Earth by way of icy planetesimals (large comets) formed beyond the frost line colliding with Earth during Period of Heavy Bombardment.

How do we explain the existence of our large Moon?

Giant Impact Mars-sized object collided with Earth during the Period of Heavy Bombardment.

When did the planets form? We cannot find the age of a planet, but we can find the ages of the rocks that make it up. We can determine the age of a rock through careful analysis of the proportions of various atoms and isotopes within it. (isotopes: atoms with same number of protons, but different number of neutrons)

Radioactive Decay  Some isotopes decay into other nuclei.  A half-life is the time for half the nuclei in a substance to decay.  Potassium (K) spontaneously decays into Argon (Ar).  Some isotopes decay into other nuclei.  A half-life is the time for half the nuclei in a substance to decay.  Potassium (K) spontaneously decays into Argon (Ar).

Age Estimation Via Radioactive Decay 40 K has a half-life of 1.25 billion years  decays to 40 Ar New rock has 100% 40 K and 0% 40 Ar. Rock that is 1.25 billion years old has 50% 40 K and 50% 40 Ar Measure ratio of 40 K-to- 40 Ar  tells age of rock (high ratio  young rock, low ratio  old rock) 14 C (Carbon-14 dating) has a half life of only ~5700 years  not suitable for dating objects millions orbillions of years old (it’s a common myth that carbon-14 dating is used to determine how old the Earth is or how old dinosaur bones are) 238 U decays to 206 Pb with a half-life of 4.5 billion years  get consistent ages with 40 K- 40 Ar studies.

When did the planets form? Radiometric dating gives us time since rock crystallized (so the melting and re-forming of rock, such as inside a volcano, “resets” the clock for radiometric dating  rock is “young” again.) Planets, including Earth, probably formed 4.5 billion years ago. Oldest meteorites are 4.55 billion years old. Oldest moon rocks are 4.4 billion years old. Radiometric dating gives us time since rock crystallized (so the melting and re-forming of rock, such as inside a volcano, “resets” the clock for radiometric dating  rock is “young” again.) Planets, including Earth, probably formed 4.5 billion years ago. Oldest meteorites are 4.55 billion years old. Oldest moon rocks are 4.4 billion years old.

Chapter 6 Study Guide 1)Solar System (SS) – Sun, 8 planets (4 terrestrial, 4 Jovian), dwarf planets, asteroids, comets 1)Sun – >99.9% of total mass of SS, 98-99% hydrogen/helium 3) Terrestrial planets – small, near Sun, rock/metal, high density, no/few moons, no rings 4) Jovian planets – large, far from Sun, gaseous (mostly H/He/hydrogen compounds with small rock/metal cores), low density, many moons, ring system 5) Asteroids – small, rocky/metal objects mostly in asteroid belt between Mars and Jupiter (not remains of shattered planet!) 1)Solar System (SS) – Sun, 8 planets (4 terrestrial, 4 Jovian), dwarf planets, asteroids, comets 1)Sun – >99.9% of total mass of SS, 98-99% hydrogen/helium 3) Terrestrial planets – small, near Sun, rock/metal, high density, no/few moons, no rings 4) Jovian planets – large, far from Sun, gaseous (mostly H/He/hydrogen compounds with small rock/metal cores), low density, many moons, ring system 5) Asteroids – small, rocky/metal objects mostly in asteroid belt between Mars and Jupiter (not remains of shattered planet!)

Chapter 6 Study Guide 6) Comets – icy bodies beyond Neptune in Kuiper belt ( AU) or Oort cloud (~50,000 AU) 7) Rules of Solar System I: all planets orbit Sun in same direction in same plane (most planets rotate in same orientation too) 8) Rules of Solar System II: planets divided into inner terrestrial and outer Jovian planets 9) Rules of Solar System III: asteroids, comets exist 10) Exceptions: Venus and Uranus’s strange rotation, Earth’s large Moon, water on Earth 11) Nebular theory best describes formation of Solar System 6) Comets – icy bodies beyond Neptune in Kuiper belt ( AU) or Oort cloud (~50,000 AU) 7) Rules of Solar System I: all planets orbit Sun in same direction in same plane (most planets rotate in same orientation too) 8) Rules of Solar System II: planets divided into inner terrestrial and outer Jovian planets 9) Rules of Solar System III: asteroids, comets exist 10) Exceptions: Venus and Uranus’s strange rotation, Earth’s large Moon, water on Earth 11) Nebular theory best describes formation of Solar System

Chapter 6 Study Guide 11) See Summary of Solar System Formation earlier in this lecture  conservation of angular momentum, energy play an important role, dust  planetesimal  planet 12) Inside frost line only rock and metal could condense (terrestrial planets + asteroids), outside frost line rock/metal/hydrogen compounds (ices) could also condense (Jovians + comets) 13) As Jovians grew via accretion, they attracted large amounts of H/He and grew very large 14) Jovians acted like mini-Solar Systems  moon systems 15) Planet growth ended when young Sun turned “on” and generated a solar wind that blew away remaining gas 11) See Summary of Solar System Formation earlier in this lecture  conservation of angular momentum, energy play an important role, dust  planetesimal  planet 12) Inside frost line only rock and metal could condense (terrestrial planets + asteroids), outside frost line rock/metal/hydrogen compounds (ices) could also condense (Jovians + comets) 13) As Jovians grew via accretion, they attracted large amounts of H/He and grew very large 14) Jovians acted like mini-Solar Systems  moon systems 15) Planet growth ended when young Sun turned “on” and generated a solar wind that blew away remaining gas

Chapter 6 Study Guide 16) “Exceptions” believed to be caused by an early “Period of Heavy Bombardment” – large bodies hit Venus, Uranus (changing rotation), and Earth (stripped matter formed Moon, water brought to Earth by comets) 17) Age of Earth/Moon determined from radiometric dating(for example, Potassium-40 turns slowly into Argon- 40), NOT carbon-14 dating (half-life for decay is way too short) 16) “Exceptions” believed to be caused by an early “Period of Heavy Bombardment” – large bodies hit Venus, Uranus (changing rotation), and Earth (stripped matter formed Moon, water brought to Earth by comets) 17) Age of Earth/Moon determined from radiometric dating(for example, Potassium-40 turns slowly into Argon- 40), NOT carbon-14 dating (half-life for decay is way too short)

Chapter 7 Earth and the Terrestrial Worlds

Mercury craters smooth plains cliffs no atmosphere “a geologically dead” world

Venus Volcanoes Few craters very thick atmosphere extremely hot surface Radar view of a twin-peaked volcano

Earth volcanoes few craters mountains riverbeds moderate atmosphere liquid water

Moon craters smooth plains no atmosphere “a geologically dead” world

Mars some craters volcanoes very thin atmosphere (dried) riverbeds? Insert ECP6 Figure 7.26

Why have the terrestrial planets (plus Earth’s Moon) turned out so differently, even though they formed at the same time from the same materials? Geological activity (or lack thereof) is the key

Earth’s Interior  Core: Highest density; nickel and iron  Mantle: Moderate density; silicon, oxygen, etc.  Crust: Lowest density; granite, basalt, etc.  Core: Highest density; nickel and iron  Mantle: Moderate density; silicon, oxygen, etc.  Crust: Lowest density; granite, basalt, etc.

Why do water and oil separate? A)Water molecules repel oil molecules electrically. B)Water is denser than oil, so oil floats on water. C)Oil is more slippery than water, so it slides to the surface of the water. D)Oil molecules are bigger than the spaces between water molecules. Full credit for all answers, even if you are wrong. A)Water molecules repel oil molecules electrically. B)Water is denser than oil, so oil floats on water. C)Oil is more slippery than water, so it slides to the surface of the water. D)Oil molecules are bigger than the spaces between water molecules. Full credit for all answers, even if you are wrong.

Why do water and oil separate? A)Water molecules repel oil molecules electrically. B)Water is denser than oil, so oil floats on water. C)Oil is more slippery than water, so it slides to the surface of the water. D)Oil molecules are bigger than the spaces between water molecules. Full credit for all answers, even if you are wrong. A)Water molecules repel oil molecules electrically. B)Water is denser than oil, so oil floats on water. C)Oil is more slippery than water, so it slides to the surface of the water. D)Oil molecules are bigger than the spaces between water molecules. Full credit for all answers, even if you are wrong.

Differentiation  Gravity pulls high- density material to center.  Lower-density material rises to surface.  Material ends up separated by density.  Differentiation happened when planet was still hot and liquid/molten.  Gravity pulls high- density material to center.  Lower-density material rises to surface.  Material ends up separated by density.  Differentiation happened when planet was still hot and liquid/molten. Important concept!

Terrestrial Planet Interiors  Applying what we have learned about Earth’s interior to other planets tells us what their interiors are probably like, mainly from their average densities.

What causes geological activity? A planet’s internal heat determines the amount of geologic activity  key point of understanding!

Can Rock Flow?  Rock stretches when pulled slowly (especially when very warm) but breaks when pulled rapidly.  The gravity of a large world pulls slowly on its rocky content, shaping the world into a sphere.  Bodies over 500 km in diameter will become spherical in ~1 billion years by slow, slow deformation of rock by gravity.  Rock stretches when pulled slowly (especially when very warm) but breaks when pulled rapidly.  The gravity of a large world pulls slowly on its rocky content, shaping the world into a sphere.  Bodies over 500 km in diameter will become spherical in ~1 billion years by slow, slow deformation of rock by gravity.

Heating of Planetary Interiors  Accretion and differentiation when planets were young Potential energy  kinetic energy  heat  Radioactive decay in core is most important heat source today (Uranium, Potassium, Thorium)  Accretion and differentiation when planets were young Potential energy  kinetic energy  heat  Radioactive decay in core is most important heat source today (Uranium, Potassium, Thorium) When Earth was young Now