1 Announcements Mid-term Exam #2, this Wed, Oct 15th. Extra-credit write-ups (Monsters, Dempsey) due today. Updated Grades online now (including HW#2).
2 Last Time Jovian planets: Giant, massive, gas-rich, far from sun (5 30AU). Formed Ice cores which gathered up the abundance hydrogen and helium. Mostly hydrogen. Clouds of ammonia, methane, strong weather. Magnetic fields (strongest in jupiter): aurora.
3 Last Time Jovian Moons: many, including some larger than the planet mercury! Formed in orbit. Tidal heating important. IO has volcanoes, europa liquid water under a thick sheet of ice, titan a dense atmosphere, lakes of hydrocarbons, and coastlines.
4 Last Time All jovian planets have rings, formed and shaped by small moons within them. Asteroids: mostly in band between Mars and Jupiter. A failed planet kept from forming by Jupiter s gravitational tugs. Cratered, and rocky. Not large enough for gravity to pull them into round shapes.
5 Last Time Meteor (falling star) vs. meteorite (chunk os asteroid, or even moon or another planet, which has fallen to earth). Comet: an ancient icy body. Near the sun, has two tails of material pointing away from the sun. Come from the Kuiper Belt, and the much larger oort cloud which stretches half way to the next star.
6 Last Time Pluto not like other jovian planets: small, icy, eccentric orbit. No longer called a planet, but a dwarf planet, one of many objects in the kuiper belt (including some larger than pluto).
7 How Solar Systems Form A cloud of gas and dust (the solar nebula ) collapsed under its own gravity. The nebular theory for solar system formation.
8 The Nebular Theory Where did the solar nebula come from? The cloud came from the left over material from a previous generation of stars
9 The First Stages of the Formation of the Solar System Initially the cloud is large and diffuse As gravity causes the cloud to collapse, it heats up and starts to spin faster The heating and spinning up are due to the conservation of energy and angular momentum
10 The First Stages of the Formation of the Solar System The result of this process is a flattened disk of gas and dust composed of 98% Hydrogen/Helium, and 2% heavier elements The orderly motions of the solar system are a direct result of the solar system s birth in a spinning flattened cloud of gas and dust
11 We see evidence of disks in other regions of the Milky Way galaxy currently forming stars
12 Temperature in the Solar Nebula The inner parts of the disk are hotter than the outer parts Rocks can condense out at higher temperatures than ice
13 The Frost Line Inside the frost line, it is too hot for hydrogen compounds to form ice Outside the frost line, it is cold enough for ices to form. Orbit of Jupiter
14 Planetesimals Tiny solid particles stick together to form planetesimals This process of assembly is called accretion Planetesimals inside the frost line are metal and rock while planetesimals outside the frost line also contain ices, and so are larger.
15 Moons of Jovian Systems Moons of Jovian systems form in miniature disks of their own Early Jupiter Early Sun
16 What is the origin of the asteroids and comets? Asteroids and comets are leftover planetesimals Asteroids are rocky because they formed inside the frost line Comets are icy because they formed outside the frost line
17 How do we explain the exceptions to the rules? Earth s moon was probably created when a large planetesimal (the size of Mars) slammed into the young Earth Similar events may explain the tilt of Uranus or the backwards rotation of Venus
18 Other solar systems Extra-solar planets
19 Extra-solar planets Very (very) recent discoveries: direct evidence for planets around stars aside from our sun. First found in Very difficult to find.
20 Finding Extra-solar planets Stars are too bright, and planets are too faint: seeing planets directly very difficult. Main techniques are Indirect: Infer a wobble of the star as one or more planets orbit it. Find solar systems aligned with our view in which the planet transits in front of the star. Look for star to change brightness.
21 Wobble Method We detect an unseen planet by looking for the periodic motion of the star We use the Doppler shift to detect this motion in the star s spectrum Shifts of ~10 m/s (100m sprinter!)
22 Wobble Method We detect an unseen planet by looking for the periodic motion of the star We use the Doppler shift to detect this motion in the star s spectrum Shifts of ~10 m/s (100m sprinter!)
23 Another Wobble Method Looking at the plane of the solar system from 30 light years away. Sun moves around by tiny amounts (millionths of an arcsecond!).
24 Transit Method Planet Transits in front of star, partially blocking it (an eclipse!).
25 Transits artist conception The fraction of the starlight blocked tells us how big the planet is. Only works for planets with orbits edge-on.
26 Workbook Time! Groups, please. If you forgot your workbook, find someone who has one. Do Motions of Extra-solar planets, page 117.
27 What have we found? As of this week, 313 extra-solar planets have been found. Many very unusual : jupiter sized or larger, closer to their star than earth is to sun.
28 artist s drawing 55 Cancri s solar system
29 Have we seen any directly? Sort of: in 2005, infrared satellite was used to see dimming of star +planet as planet went behind star. Difference is direct light from planet!
30 Atmospheres detected Transit method very powerful: see change in starlight as it passes through planets atmosphere. Some dry Other with evidence of water!
31 Mapping the weather!
32 What have we learned? Nebular model needs revision. Planets must be able to migrate inwards.
33 What about Earth? No Earth-like planets found to date. BUT, Doppler technique is not sensitive enough to find Earthlike planets We just do not know much yet.
34 Super-Earths In the last several years, finding planets with masses 3 10 the mass of the earth. Some very close to their stars (2 day orbit!). Smallest 3.3 earth masses, orbiting a very cold brown dwarf star.
35 Gliese 581c: In the zone Discovered earth s mass. 13 day period. Orbits close to a cool red dwarf star. Is in the habitable zone, where water would be liquid!
36 Mid-Term Exam #2 Wed., Oct 15, in class. 50 multiple choice problems. Buy-back extra credit will be available (keep your tests, and mark you answers!). Covering 3.3 (Kepler s laws), 4, 6 9 Use: end of chapter guides, online Study Area quizzes.
37 Mid-Term Exam Topics Kepler s laws. Speed of planet during orbit (equal areas in equal time). P 2 =A 3 Mass vs. Weight. Speed vs. Velocity. Newton s laws of motion: ❶ Body at rest stays at rest (or constant motion). ❷ Force = mass acceleration. ❸ Equal and opposite force. How they apply.
38 Mid-Term Exam Topics Types of Energy (kinetic, radiative, potential, mass-energy). Energy is conserved. Tides and their relation to phases of the moon. Newton s universal law of gravitational force: how does it depend on mass, distance? How newton s law underly kepler s law (e.g. angular momentum most be conserved: Equal areas in equal time!).
39 Mid-Term Exam Topics Terrestrial vs. Jovian planets. Size of planets (e.g. compared to earth, compared to Jupiter, compared to sun). Ordering of planets. Internal layers of terrestrial planets: Core, mantle, crust. Volcanism and plate tectonics: a result of internal heat. Erosion.
40 Mid-Term Exam Topics Cratering as an indication of the age of a planet s surface. What can heat planets/moons: radioactivity, differentiation, tidal heating (e.g. IO). Meteor vs. meteorite Aurora and magnetic fields. Jovian Moons: what makes them special?
41 Mid-Term Exam Topics Solar nebula: what s it made of (mostly)? Pluto demoted and dwarf planets. Kuiper Belt, Oort cloud, objects of the K.B. What s a greenhouse gas? Asteroids and the asteroid belt. Comets. Formation of both. Sizes of asteroids. Extra-solar planets: how we detect them?