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ASTR 150 ‣ ‣ ‣ Homework 2 due Monday Planetarium: Last shows next week (M-Th) Next Monday/ Wednesday no lectures ‣ ‣ ‣ Time for asteroid lab Last time: Solar System Formation Today: Solar System Formation 2 Music: It Overtakes Me/The Stars Are So Big, I Am So Small... Do I Stand A Chance? – Flaming Lips 1 Taking The Solar System for a Spin Solar nebula competition: Gravity vs Angular Momentum • If fall perpendicular to spin axis Need to speed up resistance: centrifugal force • If fall parallel to spin axis: same speed, so no resistance forms protoplanetary disk swirling gas and dust raw material for planets – Origin of planet’s orbits! – Origin of Ecliptic plane – Organizes spins along initial spin axis Q: how can we test if these ideas are right? 2 Why do large bodies in our solar system have orderly motions? The solar nebula began to collapse due to its own gravity As it collapsed, it began to spin faster and faster Sun forms at the center, surrounded by a flattened disk Planets form from gas and dust in the disk 3 The orderly motions of our solar system are a direct result of the solar system’s birth in a spinning, flattened cloud of gas Not all mass falls in directly (radially). Why? All gas has a small spin that preferentially causes the formation of a flattened structure Disks around Young Stars are Common 4 Disks have been imaged with HST’s infrared camera Young stars are surrounded by dense disks of gas and dust 5 From dust grains to planetesimals to planets http://www.metacafe.com/watch/1111454/formation_of_the_solar_system_great_animation/ 6 When the temperature is low enough, molecules condense (solidify) from the solar nebula into dust grains Grains collide and stick: get larger by accretion Grow into planetesimals (~1 km across) Planetesimals collect into planets From dust grains to planetesimals to planets Dust grains are the ‘seeds’ of planet formation 7 When the temperature is low enough, molecules condense (solidify) from the solar nebula into dust grains Grains collide and stick: get larger by accretion Grow into planetesimals (~1 km across) Planetesimals collect into planets iClicker Poll: What made what? Solar nebula collapse leads to ‣ ‣ pre-Sun (“protostar”) forming in center surrounded by disk of gas and dust which will lead to planets, comets, asteroids What will make what? A. B. C. D. Earth mostly made of disk dust, Jupiter mostly made of disk gas Earth and Jupiter mostly made of disk gas Earth and Jupiter mostly made of disk dust Earth mostly made of disk gas, Jupiter mostly made of disk dust 8 Answer A What are the ‘seeds’ made of? ‣ ‣ ‣ The ingredients of the solar nebula fell into four major categories Hydrogen/helium gas (98% of mass) do not condense to form solids or ices Other components can condense at the right temperature i.e., planet seeds! 9 Everything astronomers know about the solar system and star formation suggests that the solar nebula was a fragment of an interstellar gas cloud. Such a cloud would have been mostly hydrogen with some helium and minor traces of the heavier elements. The original chemical composition of the solar nebula should have been roughly the same throughout the nebula. Planet Formation in the Disk Heavy elements clump 1. Dust grains collide, stick, and form planetesimals– about 1012 of them, sort of like asteroids! All orbit in the same direction and in the same plane. 2. Gravity Effects: Big planetesimals attract the smaller planetesimals. So, fewer and fewer of large objects (100’s). Collisions build-up inner planets and outer planet cores. 3. Collisions can also account for odd motions of Venus (backwards), Uranus (rotates on its side), and Pluto (high inclination of orbit). Proof of period of high collision evident on moon 10 Why are there two types of planets? 11 Temperature Controls Planet Formation The inner nebula was hot: ‣ ‣ and only metals and rock could condense there no ices can form The outer nebula was cold, ‣ ‣ ices could condense in addition to metal and rock Boundary: “snow line” or “frost line” ‣ closest place where ice can survive too hot for ice! ices can exist 12 The important factor was temperature. The inner nebula was hot, and only metals and rock could condense there. The cold outer nebula could form lots of ices in addition to metals and rocks. The frost line seems to have been between Mars and Jupiter—it separates the formation of the dense terrestrial planets from that of the low-density Jovian planets. i>clicker question 13 Answer B Terrestrials vs. Jovians Inner solar system ‣ Metal & rock seeds ‣ Less material ‣ Small, rocky planets Outer solar system ‣ Ices, rock & metal seeds ‣ More material ‣ Proto-planets grow big ‣ Gravity captures large amounts of H and He gas ‣ Large, gaseous planets Jovian planets grew massive enough to gravitationally capture gas from disk 14 Where did the asteroids and comets come from? 15 Planetesimals The young solar system was filled with trillions of planetesimals Many were swept up to become parts of the forming planets What happened to the rest? 16 Heavy Bombardment Leftover planetesimals bombarded other objects in the late stages of solar system formation Evidenced by the cratered surfaces of the Moon & Mercury! Period of heavy bombardment Lasted for about 800 million years The Moon’s surface shows the scars of the heavy bombardment 17 Fates of the planetesimals Swept up by forming planets or ejected from solar system Near terrestrials - swept up But some remain... Asteroids and comets are le6over planetesimals! Asteroids are rocky because they formed inside the frostline Comets are icy because they formed outside the frostline 18 Ceres is the largest of the rocky leftovers Pluto & Eris are the largest of the icy leftovers Origin of Asteroid Belt ‣ ‣ ‣ Planetesimals between Mars and Jupiter did not gravitationally clump into a planet Jupiter’s gravity stirred up these planetesimal orbits and prevented clumping Asteroid belt is leftover planetesimals prevented from ever forming a planet The asteroid belt is not the remains of a destroyed terrestrial planet 19 Jupiter ejected most asteroids from the Solar System or sent them on orbits to collide with the forming terrestrials Kuiper Belt Objects: Formed beyond the orbit of Neptune Not enough material to form another Jovian planet 20 enough, they would. . ltlroLrqh B u i F e r n a n d e z a n d I p n o t i c e d s o m e t h i n g e 1 s eA t h c s j n r u l a t e dg i a n t p l a n e t ss t a r t e da t c e r t a i r dl i s t a n ( ' t 'i l o l x the Sun, they inevitably ended up at very different plat'cs. This discovery planted the seed that ultimately grew rirtcl e t e s i m a l ,c a u s i n g1 1 1 ,3i l r r t ' i ' ' r L ic l ' ) s el ' t o t h e S u n ' N e p j n t o a n o r : b i tj u s t t u n e i t s e l f t r c c t l c r a t e tIliai t \ i - - i -i l c l i t t o v e d a s k o s hf a r t l r c ri t ' o l l tt t , \ l r N o w h e r e ' st h e k e r : \ \ i ' , , l \ c 1 r t r - r n ed r o p p e d a P l a n e t e s i ' ' - : rre\-er calrle back. Why? n r a li r t w a r d , t l r a t o b ; c 'rB e c a u s et h e b o d v f e l l r l - t ,' l l r ' :r'ar itational griP o{ one of t h e o t h e r g i a n t P l a n e i t T l l c t .rrei plaver was (and still is) 'J J u p i t e r ,w h i c h h a s r o L t { r r l r t i m e s t h e m a s s o f U r a n u s Oort Cloud Comets: Ejected to deep freeze the Nice model. Take Neptune as an exalnple, says Levison' Whenetcr' the planet, with its strong gravitational field, encountcrcd a t i n y p l a n e t e s i m a l ,i t h a d a b o u t a u e v e n c h a n c e o i s t ' a t t e r - .ro Oort Cloud comets formed in Slingshots Plqnetory theW hJovian planet region o n d o w o yf r o m t h e S u n ,o n d e no s m o l lo b i e c tP o s s e s c l o s et o o p l o n e t ,g r o v i t o t i o n o l interoctionschongeboth tro' iectories.The orbit of the much moremossivebodYolterso m i n u s c u lo e m o u n t ,b u t o f t e r t o i l sw i t h s e n d i n gi t c l o s e rt o t h e S u n .E v e r yt i m e t h e c o i n comesdown toils, however, we'lllet it foll to the ground, wherewe con't PloYwith it o g o i n .W h e n e v etrh e c o i n r e g i s , e ' l l f l i Pi t o g o i n . t e r sh e o d s w So if we stort our tossing w i t h , s o y ,1 O Oc o i n s ,w e ' l l f l i p o b o u to n e q u o ln u m b e ro f h e o d ss n d t o i l s .B u t s o o no u r s u p p l yw i l l b e g o n e ;o l l t h e c o i n sw i l l l i e o n t h e g r o u n d . S i m i l o r l yN, e P t u n e n d e du P f l i p p i n gm o r eP l o n e t e s i m s il ns Gravitational interactions with the proto-Jovians changed their orbits m o n yb i l l i o n so f e n c o u n t e r s , ‣ the chongesore significont. Despiteo 5O'5Ochonceof eitherof the encountersPic' tured ot right, the net resultfor "Heods" Plonetorbit 0bject Launched them to the Oort Cloud our solorsystemwos to send SoturnU , r o n u so, n d N e p t u n e o u t w o r d ,o n d l u P i t e ri n w o r d . To understondwhY,considero coin toss - with o quirk. Let'sossocioteheodswith f l i p p i n gt h e p l o n e t e s i m oulP OR ‣ \j "Toils" Sent them into the inner t o w o r dt h e S u n ,t h u s m o v i n g solar system! i t s o r b i to u t w q r d . Septentbt:r2oo7 SkY & TelescoPe This also changed the jovian planet orbits Jupiter migrated inward Other jovians migrated outward 21 Earth’s Cosmic Water Source? Interactions with Jovians may have sent waterbearing planetesimals to a young Earth 22 Either icy planetesimals or rocky planetesimals with some water from near the frost line (beyond Mars’ orbit) Recap: The Violent Birth and Infancy of the Planets Heavy Bombardment ‣ ‣ planetesimals collide with young planets lasted 800 million years Formation of the Moon: Smack! ‣ ‣ ‣ Mars-sized object collided with young earth orbiting debris clumped to form Moon collision gave Earth its 23.5 degree spin tilt Early Earth ‣ ‣ constant bombardments no water until brought by comet impacts 23 Impacts and the Earth 24 Is the impact threat a real danger or just media hype? 25 Meteors and Earth 26 Meteor Crater Near Winslow, Arizona ‣ on your way to the Grand Canyon: must-see detour! Occurred 50,000 years ago impactor: ‣ 50 meter across ‣ impact speed approximately 13 km/sec = 30,000 mph! Energy of explosion equal to 25 megatons of TNT! 1.2 km across 27 Scientists now believe that the crater was created approximately 50,000 years ago. The meteorite which made it was composed almost entirely of nickel-iron, suggesting that it may have originated in the interior of a small planet. It was 150 feet across, weighed roughly 300,000 tons, and was traveling at a speed of 28,600 miles per hour (12 kilometers per second) according to the most recent research. The explosion created by its impact was equal to 2.5 megatons of TNT, or about 150 times the force of the atomic bomb that destroyed Hiroshima. How can falling objects cause so much damage? Impacts occur at enormous speed! ‣ ‣ ‣ Space debris moving at high speeds Earth’s orbital speed: 30 km/s (67,000 mph) Impactor speeds entering the atmosphere ‣ ‣ ‣ Range: 11-72 km/s average asteroid speed: 17 km/s average comet speed: 51 km/s 28 Minimum speed - is escape velocity due to Earth’s gravity - an object falling into Earth’s gravity well will be accelerated to at least 11 km/s Why different averages? Asteroids orbit in the same direction as Earth, so the average net impact speed is lower Comets orbits go every which way, so you can get head-on collisions! Does Large Space Junk Ever Impact Objects in the Solar System? Image of the Moon with the Space Station in the foreground. Cool or what? Proof in the Pudding: Moon Pie http://antwrp.gsfc.nasa.gov/apod/ap090206.html 29 Proof in the Pudding: Moon Pie With even a small telescope, you can see >30,000 craters on the Moon. http://antwrp.gsfc.nasa.gov/apod/ap071120.html 30 • Full Moon (telescope view) with lighter highlands and darker basalt plains, filling multi-ringed basins • Apollo 16 view of Descartes Highlands, with impact craters on all scales 31 Group Discussion The Moon clearly has had some LARGE impacts over its lifespan of ~4.5 billion years. Why didn’t the Earth? – I didn’t fall into a crater on the way over here today. More than one reason! a) When your group has a good answer click A on your iClicker. 32 Earth-Moon Cratering Differences Most impactors burn up in Earth’s atmosphere ‣ the Moon has no atmosphere to protect it Earth’s surface is about 75% water ‣ most meteorites go to bottom of ocean Erosion due to wind and water slowly covers up craters on land But still, the Earth does have some craters... 33