Leftovers Gas is eventually captured or pushed out by wind from the star, but dust and planetesimals are left around

Formation of the Solar System CLOUD COLLAPSE ROTATING DISK GAS CAPTURE? CONDENSATION STEPS: ACCRETION EVIDENCE: planets orbit in same direction and same plane Sun and planets rotate in same direction disks seen around other stars young stars seen in collapsing gas clouds terrestrial planets and asteroids found near Sun jovian planets, icy moons, comets found farther away Jupiter, Saturn are mostly hydrogen and helium gaps in disks around other stars many meteorites are made of smaller bits heavy cratering on oldest planet surfaces asteroids, comets are “leftovers”

Illustration of Kepler planet candidates blocking their stars SUN +JUPITER + EARTH

Transits - A Kind of Eclipse planet crosses in front of a star, making star appear fainter  1193 planets detected so far!

Planet Transits planet star amount of starlight blocked tells us about size of planet: VIEW FROM EARTH: orbit period and estimate of star mass tells us about semi-major axis of planet:

Most planets that have been discovered around other stars are thought to be like Jupiter. The Sun is about 11 times the size of Jupiter. What fraction of the Sun’s light would get blocked if we were watching Jupiter transit the Sun from far away? A.99% B.90% C.10% D.1% E.0.1% F.0.01% Thought Question planet star

Questions!!! Why are some jovian planets found near their stars? (“Hot Jupiters”) Do jovian planets form differently than we think? Did jovian planets “migrate” in toward their stars? Why doesn’t everything have the “special direction”? Why are Venus and Uranus rotating differently? Why do some planets orbit in the opposite way that their stars rotate? Why are some jovian planets found far from their stars? What are “super Earths” and “mini-Neptunes”? Will terrestrial planet discoveries reveal something completely new?

“Hot Jupiters” orbit in as little as 0.8 Earth days! cloud-top temperatures up to 1300 K some are “puffy” – up to 30% larger than Jupiter HOW DID THEY GET THERE?

“Super Earths”/”Mini Neptunes” a variety of densities about 2-10  Earth’s mass, and up to 4x Earth’s radius How common are they? How do they form? What could they be like?

still looking for these!!

Comparative Planetology Questions: How are planets similar and different?  surface  atmosphere Why are they different?

Uncovering Planet History CRATERING: All planets heavily bombarded in past… If a planet has craters today: surface wasn’t completely protected (by atmosphere or oceans) surface wasn’t “cleaned” recently (erosion, lava flows, or tectonics) Look at:  how heavily cratered surface is  where craters are

Thought Question: What is the order from oldest to youngest? A (volcano) B (crater) C (crater) D (lava flow from another volcano)

Mercury: heavily cratered, but how long ago?

Impact Craters

Radiometric Dating of Rocks  When rock solidifies, radioactive atoms and their products are “frozen” into it … no escape! A small fraction of atoms are radioactive - breaking up and forming atoms of a different chemical element Potassium-40: Uranium-238:

Radiometric Dating Nuclei of parent species (like potassium-40) decay to become daughter products (like argon-40) half-life: time for half of radioactive atoms to decay potassium-40: 1.25 billion yr uranium-238: billion yr TOTAL K+Ar

Thought Question: Each atom of element Y will eventually decay to form one atom of element X (with a half-life of 800 million years). When the planets solidified, there was no element X. If you find a rock where element Y is currently has 1/8 th the total element X plus element Y, …how old is the rock? (Enter your answer in millions of years.) …what fraction of the original Y is left today?

FRACTIONS: PROPORTIONS: 1:1 1:3 1:7 1:15

Oldest Known Crystal 4.374±0.006 billion yr old

Ages of Surfaces Radiometric dating of Moon rocks allow us to measure when the rock was last melted… …when were most craters made?

Thought Question: This is a picture of Saturn’s moon Enceladus. Which of the following statements about its surface is probably true? (Enter the letters for all correct answers.) A.The lower left part of the surface probably froze more recently than the upper right. B.The oldest parts are about as old as the oldest parts of the Moon. C.None of the above is true.

History of Cratering most cratering in first billion years of solar system heavily cratered surfaces have changed little in last 3 billion years

1/3 Earth 1/4 Earth 1/2 Earth 95% Earth A Scatter Plot Can this help us predict terrestrial planet properties?

What Made Them This Way? VOLCANIC ACTIVITY HOW MUCH OUTGASSING? STRENGTH OF GRAVITY PLANET MASS/RADIUS DISTANCE FROM SUN TEMPERATURE CONDENSATION? HOLDS ONTO GASES?

VOLCANOES: If a planet has volcanoes: interior was hot enough for rock to move crust was thin enough to allow lava to reach surface Clues:  number of volcanoes  their pattern  are they active? Uncovering Planet History

Mars  very few volcanoes, but they are VERY large…  volcanoes probably not active

 largest number of volcanoes among terrestrial planets  evidence of active volcanoes Venus

Thought Question: Suppose a terrestrial planet the same age as Earth is discovered orbiting another star, and it is your job to predict what it is like. If the planet is known to have a mass and size smaller than Venus but larger than Mars, what would be the best prediction? A.It should have no volcanoes. B. It should have volcanoes, but they may or may not be active. C. It should have a moderate number of active volcanoes spread evenly over the surface. D. It should have a large number of active volcanoes found only in small areas of the surface.

Moon Oceans? Ganymede (Jupiter moon) Enceladus (Saturn moon)

Temperature of interior involves competition between: Terrestrial Planet Interiors HEAT NOW IN PLANET SOURCE OF HEAT HEAT LOST FROM SURFACE LEAKY BUCKET ANALOGY: thermal energy added by radioactivity: radioactive atoms release heat when they decay thermal energy lost to space: heat can only escape from planet’s surface

Terrestrial Planet Interiors thermal energy added by radioactivity: every bit of mass contains a small fraction of radioactive atoms: thermal energy lost to space: heat can only escape from planet’s surface energy added per second average density energy lost per second planet area is related to planet mass is related to

Loss of Internal Heat Terrestrial planets are losing heat (cooling) because radioactive heating is smaller, but exactly how small affects how quickly the inside cools off:

Thought Question: Based on the rates of energy being added and lost, which terrestrial planet should cool off most slowly? (Hint: compare rates of adding and losing thermal energy by thinking about the ratio.) A.Mercury B. Venus C. Earth D. Moon E. Mars

Thought Question: Mars is about half the diameter of Earth and 1/10 th the mass of Earth. Based on the energy added and lost per second, Mars probably cooled off… A.about 10 times as fast as Earth. B. about 2 times as fast as Earth. C. at about the same rate as Earth. D. about 1/2 as fast as Earth. E. about 1/10 th as fast as Earth.

The Heat Inside: Earth, Venus: still active today Mars: active volcanoes once, but not many Mercury, Moon: dead for a long time large planets take longer to cool off and solidify inside: As planets formed, collisions and radioactivity melted them into sphere shape:

Venus from the Ground

Atmosphere Conditions Average Temperature: 850 F 60 F -60 F 737 K 288 K 210 K Atmospheric Pressure: 90x Earth’s 0.007x Earth’s Chemicals: 96% CO 2 78% N 2 95% CO 2

Addition of Gases Outgassing by volcanoes Bombardment Loss of Gases: Gas escape into space Condensation Chemical reactions Terrestrial Planet Atmospheres

Where Did It Come From? Comet impacts bring “ices”: water vapor (H 2 O) carbon monoxide (CO) ammonia (NH 3 ) methane (CH 4 ) Volcanoes release gas from molten rock: carbon dioxide (CO 2 ) nitrogen (N 2 ) water vapor (H 2 O)

Escape Speeds Larger planet mass  gas molecules have to move faster to escape escape speed: Higher temperature  faster gas molecules move  easier to escape

Temperature Temperature relates to average speed of motions of atoms absolute zero (0 K) is when thermal motion stops box increases the average particle speed Gas animation

Speeds of Gas Molecules Average particle kinetic energy in a gas only depends on temperature: (Boltzmann’s constant) Gas of a particular chemical has a chance to escape over the history of the solar system if: Average particle speed in a gas:

Thought Question: What combination of factors makes it more likely to lose a gas from a planet’s atmosphere? (Enter a three letter answer.) A.High mass planet B.Low mass planet C.High temperature planet D.Low temperature planet E.High-mass gas molecules F.Low-mass gas molecules

Thought Question: How does the average speed of a hydrogen molecule (H 2 ) compare to the average speed of an oxygen molecule (O 2 ) at the same temperature? (H 2 has twice the mass of hydrogen atom, and O 2 has 32 times the mass of a hydrogen atom.)