Dr. Henry Throop / University of Colorado Astronomy 1110 June 26, 2000 Lecture 16: Formation of the Solar System; Pluto Announcements ------------- HW #4 -- due Wednesday, but I'll return any turned in on Tuesday in time for Exam #2 Final: will be cumulative Exam #2: covers giant planets, rings, satellites, formation of SS, collisions, ESP's Perhaps a bit of current events Press conference: Real Video anyone? www.spaceref.com? Friday: SCHEDULE CHANGE! Sun & Stars -> Spacecraft Design (ch. S2) Monday: SCHEDULE CHANGE! Holiday, no class Observing: later this week? Monday? Wednesday? Extra credit -or- math redo assignment (sand grains on mars?) HW #3: (p)2 = 4 pi2 (a)3 / (G (M1 + M2)) Formation of SS --------------- Key observations that must be reproduced in a model Planets move in same direction Planets move, spin the same Satellites move, spin same as planets There are some exceptions (Retrograde spins -- not retrograde motion!) Circular orbits (almost) Planet properties generally move Less dense further out More gas further out Bigger Further apart German philosopher Immanuel Kant in 1755 hypothesized the origin of the solar system as beginning with a rotating gaseous nebula out of which condensed globular bodies that became the sun and planets---all revolving in the same direction. Essentially the same theory, now called "the nebular hypothesis" was proposed by the French mathematician Laplace in 1796. Solar nebula model Start off with a cloud (`Solar Nebula') 1. Cloud Collapse a. Cloud collapses radially (due to gravitation) b. Cloud heats up as it collapses (like a compressor) c. Cloud spins faster as it collapses (like ice skater pulling in arms) d. Motion becomes less chaotic and more smooth (like pepper flakes on water) 2. Condensation a. Rocks, metals, ices condense from gasesos -> solid i. Metals condense near Sun; ices condense far away; rocks in between ii. Location depends on how hot nebula is and freezing point of each ingredient 3. Growth of Planets & other bodies a. Grains collide & grow: mm -> cm -> m -> km -> planetesimals -> planets Demo: sand in a cup? b. Cores of Jovian planets sweep up & attract gas c. Random collisions: reverse spin of Uranus, create Earth's Moon, etc. 4. Cleaning it Up a. Remaining gas & dust is blown by sun back into interstellar space 5. Denouement a. Still have ongoing collisions with leftover pieces: asteroids, comets, dust i. Delivery of water to our oceans (we're drinking comets!) ii. Spread of life throughout solar system? (Are we martians?) Q: Why do we believe this? -------------------------- A: Because we see it happening elsewhere, and it fits all the data that we can observe here. Q: Problems with this model o Doesn't explain distance between planets o Most stars form in OB assocs? Q: Why didn't KBO's stick together (erosional vs. accretional)? A: Don't know. Lower velocities? Colder? Earth-Moon system ----------------- Obs: Moon orbits over equator Looks like Earth's crust Looks same age as earth Popped out from Ocean: great, but Earth was spinning too fast (child) Formed simultaneously: composition doesn't match (sister) Capture: hard to do dynamically (stepchild) Giant impact: works pretty well. Violent. Most of system was probably already melted at the time. Break ----- Pluto ----- Q: where does it fit in? r = 1200 km mass: 10x smaller than mercury Nothing like giant planets For planet: Round (ie, not an asteroid) Closer than KBO's Large Historically a planet For KBO: Largest of a continuum of sizes Wouldn't be called a planet today A lot smaller than it was `supposed' to be For Comet: Has a tail sometimes Elliptical, tilted orbit Atmosphere collapses & expands, just like comet Icy For weird: Double planet Never been explored For this being a silly Q: Why do we have to classify everything into one of 2 or three categories? A: because that's what scientists do: classify things! History: 3 yrs ago, L. Esposito started it 1 yr ago, IAU had a _vote_. IAU = assigns names to asteroids, comets, impact craters, etc. e.g., craters on venus = women Made statement: Pluto is a planet Images ------ Beta Pic Orion Disks (HST + thesis sketches) HD4796A ESP encyclopedia VG: Pluto discovery image VG: Pluto atmosphere occultation / KAO Stats: how many KBO's vs. pluto? add: earth-moon origin Demos ----- Roundabout chair Pepper demo Q: why do does everything get hot? A: Because you have friction, _and_ gas is compressing Like rubbing hands together Like back end of refrigerator compressor: puts off heat Like squeezing a balloon (?) Get: ---- Pepper Container CD player Collab Q's ---------- Consider these other scenarios for formation of SS. What are problems? Other models: Sun formed in place, then planets accrete from ISM around it Planets popped out from Sun Planets were captured from other solar systems Is Pluto a planet or not? If the Early solar nebula were hotter... Jovian planets would attract more gas Ices would form futher out in disk Pluto would be formed closer The Earth would have two moons