Planetary Science Overview

1. Planetary Science Overview GLG-105/Sec. 1 Spring, 2009 Instructor Kevin Mullins Text An Introduction to the Solar System McBride and Gilmour

2. Intro • We live on a fairly small, rocky planet that circles a common, ordinary star that is in turn a miniscule part of an average galaxy. Four things make our planet somewhat extraordinary by the standards we know today: 1) it is very dynamic, 2) it contains water in all three physical phases, 3) it has a large Moon to-planet-ratio, and 4) it is crawling with carbon-based life forms.

3. Stats • 13.7 by age of the Universe • 4.6 by age of the Earth and our Solar System • 186,000mps speed of light • 5,878,625,373,183.61 mi distance of a lightyear • 5.878trillion mi • 63,241 astronomical units • A.U. 93million mi • To reach the Earth it takes light…. • ~1.3 sec from Moon • ~8.3 mins from Sun • 35-52mins from Jupiter • ~5.5hrs from Pluto • >4.3yrs Alpha Centauri • 9yrs Sirius in Canis Major • 2.5my Andromeda Galaxy • 2by Abell 2218

4. Planetary Size Comparison “When I look up at all the stars in the dark, night sky, I’m struck by how insignificant they are….”

5. Sirius 8.6 ly brightest star in the sky Canis Major Double star system Arcturus 36.7 ly red giant Brightest star in the constellation Bootes 3rd brightest star in the nighttime sky after Sirius and Canopus

6. Comparison of the Sun, Antares, Arcturus and the orbit of Mars

7. So much for the Sun being impressive….

8. Fundamental Concepts • Biggest mysteries in understanding the cosmos lie in our lack of knowledge regarding “origins” • Early massing of matter into astronomical “units” (stars and galaxies) generated little detectable radiation • Theories on how matter ought to behave under such conditions • Few points to check theories against observational data • Still, various phases of such formation appear visible but the trigger mechanisms are poorly understood • When searching for evidence of the origin of planets information gets even more sparse • Lack observational data • And clear, unflawed theories of planet formation • Until recently, only our SS as evidence for planetary formation • Newly discovered planets are biased toward one type that is of considerable difference from accepted theories of where, what composition, and how large, gaseous planets should form

9. Historical Perspective • Nicolaus Copernicus (16th Century) – Heliocentric SS • Sun at center of Universe • Earth rotated • Johannes Kepler (17th Century) – 3-laws of planetary motion • Using Tycho Brahes observational science • Planets travel in ellipses • Sweep out equal areas in equal time • Orbital period is tied to orbital radius • Galileo Galilei (18th Century) - builds first telescope • Ground his own lens to improve and created 30X magnification • Venus phases: evidence that it orbits the Sun • Sir Isaac Newton – Law of Gravity • 3 laws of motion • Albert Einstein – General Theory of Relativity • Preferred static universe • General relativity however didn’t fit this idea and instead suggested it was expanding • Fabric of space and time

10. Historical Perspective(cont-d) • George Lamaitre - Catholic priest • “In the beginning” • Based on Einstein’s equations • Universe is expanding therefore it must have been smaller • Fred Hoyle - “Big Bang” • Steady State proponent • Stellar nucleosynthesis • Edwin Hubble • Red-shift theory • Age of Universe was too low due to inaccuracies in observational data • Andromeda is a galaxy 2.5mly away • 186mi/sec approaching Sun one of few blue-shifted objects • Measurement of remnant energy of heat from BB • Change in wavelength to longer = radio waves • Bob Wilson and Arno Penzias – • Bell Labs Big Horn Antenna – static echo or residue • No clean signal random, pigeon droppings in horn of telescope • Alan Guth (1980) inflation • phase of exponential expansion that was driven by a negative-pressure vacuum energy density

11. All-sky Microwave Map • Microwave distribution based on Wilkinson Microwave Anisotropy Probe (WMAP) satellite • 13.4 by temperature differences • Red = warm Blue = cool • Remnant energy from 360,000y A.B.

12. Hubble TelescopeDeep Field Image • Deep Field Experiment • 11 day exposure of small dark area of the sky <100th of Moon diameter • Reveals vast amount of material and extends limits of Universe out to 13bly

13. Einstein Rings • Hubble image of Abel Cluster 2218 • Gravitational lensing • Likely confirmation of presence of dark matter • Confirmation of Theory of Relativity

14. The Big Picture The Big Bang

15. 380,000 yrs • “Decoupling stage” • Photons can escape collisions and universe becomes transparent • Remnants of energy burst is that measured by Wilson and Penzias • 1 by first stars begin to form • Large, hot and short lived • Novas create new elements like N, O ,C • 9 by gravity and matter form normal, yellow G-type star Sol

16. What is the shape of space? • If mass is high it will be spherical or closed • If mass is at critical level it will be flat • If mass is low it will be open, infinite with a negative curvature

17. 3-Possible Futures for Universe • Based on amount of matter in universe • M>1 universe is closed and collapses • M=1 universe continues to expand but slows asymptotically • M<1 universe continues to expand at an ever increasing rate • Big Rip all is torn apart

18. Accelerating Universe • 1998 discovery of accelerating universe • Dark matter is theorized • Anti-gravity or repulsive force • Accounts for 73% of matter in universe • Evidenced by “gravitational lensing”

19. Galaxy Classification • Edwin Hubble first created classification system • Forms vary from irregular to bar spirals • Once thought to represent evolution

20. Irregular GalaxyThe Large Magellenic Cloud • Small with no bulge and an ill-defined shape • No apparent rotational center • Out of disk plane • Caught in gravitational pull of larger galaxy • Lose mass • Pass through spiral arms • Eventually assimilated

21. Elliptical GalaxyM87 • Classified depending on how elliptical • Uniform luminosity • Similar to the bulge in a spiral galaxy, but with no disk • Old stars • Little to no gas present • Ellipticals are usually found in the high density field, at the centre of clusters

22. Lenticular GalaxySombrero GalaxyNGC4549 • Possess both a bulge and disk but no spiral arms • Little or no gas • All the stars are old

23. Spiral GalaxiesM100 • Characterized by presence of gas in disk • Star formation remains active • Younger population of stars • Usually found in the low density galactic field • Avoid disruption by tidal forces from neighboring galaxies • Retain delicate structure

24. The Milky Way Galaxy • 100,000ly across • 100-200billion stars • May have bar structure • Just left the Orion Arm • 225million yrs = a cosmic year • Galactic Center • 26,000ly away • Black hole • 2.6million x mass of Sun • Behind star and dust clouds in Sagittarius • Part of Local Group • 2nd largest galaxy behind Andromeda • 46 galaxies • 10million ly across

25. Andromeda Galaxy • Our nearest large neighbor • 1-trillion stars • MW may have more dark matter • Hubble • One of farthest away objects that can be seen by naked eye • 2.5mly away • Hubble proves outside our MW • Approaching Sun @ 186mi/sec • One of few blue-shifted objects

26. Early Stars • H –He only elements available • 1st stars were massive, hot, short lived • 150 Sun masses • 1million yrs lifespan • Created heavier elements when supernova’d • Later hypernovas create even heavier elements up to Uranium • Most stars believed to be on 2nd or 3rd life cycle • “We are stardust”

27. StarsMajor Concepts • Elements such as N, O, C, Fe were produced by nuclear processes that generally occur in stars • Often these elements are re-injected in to interstellar space through novas/supernovas • Dispersed elements maybe re-concentrated or recycled to form new stars or planets

28. Formation of Proto-stars • Gas cloud more than 50 light years in diameter • Not dense only a few thousand atoms/cm3 • Enough material for several SS’s • Cold only a few degrees above absolute zero • Within 400,000yrs contracted to core 1 millionth its original size (still 4x larger than today) • Heats up as particles are forced closer and closer • Begins to radiate heat and forms protosun • Few thousand years protosun collapsed to ~diameter of orbit of Mars reaching 100,800F • Atoms start to ionize and emits feeble red light • Sol is born

29. Formation of the Solar System • Nebula Hypothesis • Pierre-Simon Laplace • 18th Century • Nebular Cloud collapses under gravitational contraction • Angular momentum flattens material w/bulge at center • Stellar or planetary disc • Protostar forms • Accretion process begins sweeping up material

30. Temperature profile of early Solar System

31. Planetary Accretion Process • Condensation • Refractory vs volatiles • Cohesion or coagulation • Irregular surface • Magnetic attraction • Electrostatic attraction • 2k yrs to get 10mm diameter “dust bunnies” at 1A.U. • Accretion • 0.1 – 10km planetesimals • Gravitational focusing • Runaway growth • Planetary embryo or protoplanet • >300km gravity pulls into spherical shape • Final collisions create planet sized bodies w/little remaining material

32. Planetary Formation • Few hundred thousand yrs for planetesimals • ~10’s-100’s of thousand yrs for protoplanets to form • > by order of magnitude for each planet further out • T Tauri star blows away dust material in disc • ~100,000,000 yrs to form “final” planet sized object

33. Asteroid 25143 Itokawa • Itokawa may be a contact binary formed by two or more smaller asteroids that have gravitated toward each other and stuck together • Hayabusa images show a lack of impact craters • Very rough, boulder-studded surface • Itokawa is not a monolith but rather a ‘rubble pile’ formed from fragments that have accreted over time • Not an Earth Orbit Crossing asteroid

34. Other Solar Systems • Beta Pictoris • Infrared image • Central star with stellar disk seen edge on • Clear area ~ size of our SS

35. Exoplanets • Gliese 229 red dwarf star • Gliese 229B brown dwarf • Not large enough to initiate fusion • Most known exoplanets • > size than Jupiter • Very small orbital dimensions

36. Overview (cont’d) • Planets – cold celestial bodies formed by elemental density differentiation from material gravitationally accumulated by stellar formation • Terrestrial (rocky) • Inner Solar System • Mercury, Venus, Earth, Mars • Metallic and silicate composition • Compositional differentiation (crust, mantle?, core) • Cratering., volcanism, tectonics, atmospheres, hydrospheres • Gas Bags • Outer Solar System • Lighter elemental composition • Jupiter, Saturn, Uranus, Neptune • Icy • Pluto • Dwarf Planets

37. Overview (cont’d) Satellites (Moons) – Smaller cold celestial bodies orbiting planets Material separated from original planet formation Foreign bodies captured by gravitational attraction Usually without atmospheric formation Rocky (silicate) Our Moon, Deimos and Phobos, larger outer planet satellites surface dominated by cratering evidence of early solar system conditions Icy Europa one of the Galilean Satellites of Jupiter may or may not have a solid (silicate) core Diverse surficial conditions from heavily cratered to very recently resurfaced

38. Development of the Earth (Planets) Differentiation The separation (and eventual layering) of material through : Differences in density Suggests that material must be fluid to allow differentiation Refractory vs volatile property dictates where elemental material can/will condensate or cool Impact history of early planetesimals, protoplanets, planetary embryos Atmosphere/Hydrosphere/Biosphere The outer, lightest gases and liquids Crust – Thin, outer layer composed mostly of Si and O (silicate rocks) Mantle - Thicker layer dominated by silicates but including heavier elements such as Fe and Mg Layers based not on composition but strength Lithosphere – crust and upper mantle composing strong, rocky layer Asthenosphere – heat-softened, slow-flowing layer of still “solid” rock Core - Small inner-most layer composed of Fe and Ni Outer core is liquid – responsible for the Earth’s magnetic field Inner core is solid

39. Planetary Processes Differentiation Thermal and gravitational separation Direct link to volcanism and tectonics Composition of surface dictates reaction to impacts and resultant crater morphology Cratering Primary process Surface dating/age comparison SS conditions over time Volcanism Silicic Mafic vs felsic Icy Water Other Io – large sulfur component Tectonics Vertical vs horizontal movement Active vs inactive interior CCC Planetary Science KMullins 2005

40. Planetary Processes Fluvial Erosion Channels, drainage patterns Deposition Sedimentary rocks Channel bars and islands Deltas Water Earth, Mars Other Europa, Titan Aeolian Erosion Ventifacts, yardangs Deposition Dunes, ripples, sand seas CCC Planetary Science KMullins 2005

41. Asteroid 4179 Toutatis • Toutatis's orbital plane is closer to the plane of the Earth's orbit than any other known several-kilometer Earth-orbit-crossing asteroid, or ECA • Earth-crossing orbits on time scales of a million years • Toutatis may have the most chaotic orbit studied to date, a consequence of the asteroid's frequent close approaches to Earth • ~1kmx2kmx4km