The Solar System - II

Transcription

1 The Solar System - II Alexei Gilchrist [The Story of the Solar System]

2 Some resources o o o Section 13.3 of Voyages (references and links at end) References noted in these slides The Story of the Solar System, M Garlick, (Cambridge Uni. Press, 2002)

3 Today Earliest Fossils Timeline Big Bang Birth of Solar System Death of Solar System Earliest Fossils Terrestrial Planets Dinasaurs Extinct Atmospheres Main Sequence Terrestrial Planets Main Sequence Heavy Bombardment T-Tauri Phase Ice Giants Comets & satelites Cloud perturbed

4 Terrestrial Planets T-Tauri Phase Gas Giants Solar Nebula Protosun Planitesimals & Protoplanets Solar globule Main Sequence Ice Giants Comets & satelites Timeline T-Tauri Phase Cloud perturbed Cloud perturbed

5 Giant Molecular Cloud o o o o o o About light years across more than a million times the suns mass mostly (73%) molecular Hydrogen; rest Helium; traces of other stuff not very dense (better than a first-class vacuum) very cold (~ -250C) Something triggered it to start collapsing (supernova shockwaves?) Orien Nebula Big Bang Birth of Solar System Earliest Fossils Today Dinasaurs Extinct Death of Solar System

6 Spitzer telescope spitzer.ogg

7 Nucleosynthesis Need an injection of heavier elements from elsewhere From:

8 A supernova, the cataclysmic explosion of a dying star, drives shockwaves into a nearby molecular cloud and rips it to pieces. These fragments will later begin to collapse under their own gravity, and one of them is destined to become the Sun. [The Story of the Solar System]

9 Solar Globule o original cloud breaks into fragments 0.1 ly across; o fragments collapse under gravity o inner material falling faster... resulting in more dense heating core o Similar in scale to Oort cloud o emits in infra-red Cloud perturbed Solar globule Planitesimals & Protoplanets Solar Nebula Protosun Gas Giants T-Tauri Phase

10 A globule is a fragment of a molecular cloud, inside of which a star is being made. Because the dust and gas accelerates inwards faster near the centre than further away, the more distant material gets left behind in a shell while a dense core develops further in. The red material is background gas in a more distant, brighter and unrelated nebula. [The Story of the Solar System]

11 Protosun o Core is a ball the size of the solar system o warms up to ~10,000K o significant radiation pressure... slows outer material o core becoming opaque... heats up faster o contraction slowed... growth slowed o starts to spin faster and faster (conservation of angular momentum) Cloud perturbed Solar globule Planitesimals & Protoplanets Solar Nebula Protosun Gas Giants T-Tauri Phase

12 Origin of spinning Angular momentum is conserved before after

13 The protosun as it might have appeared billions of years ago if we had been able to peer inside the thick cocoon of gas and dust that still encased it. The surface in this depiction, which shows the protosun at an advanced stage, is now hot enough to glow, its temperature around a few thousand degrees. [The Story of the Solar System]

14 T-Tauri Phase Solar Nebula o Flattens due to rotation - turbulent pancake of gas surround core o core out to mercury; disc AU o temp ~2000K in core begins to shine o most of the globule consumed Solar Nebula Gas Giants Protosun Planitesimals & Protoplanets Solar globule Cloud perturbed

15 The Solar Nebula, a swirling pancake of gas and dust, surrounds the newly forming star known as the Sun. Later, planets will form there. [The Story of the Solar System]

16 Planitesimals o molecules and particles condense out o small particles form o resembled a vast swirling storm of snow, sand and iron filings moving at 10s of km/s o relative velocity quite minor all moving in same direction Cloud perturbed Solar globule Planitesimals & Protoplanets Solar Nebula Protosun Gas Giants T-Tauri Phase

17 Planitesimals o Different particles condensed out ar different radii o near protosun 2000K, only dense materials could condense e.g. iron o further out silicate particles o out about Jupiter, -70C, ice crystals form... snow line

18 Planitesimals o particles stick together (electrostatic?) accretion o pebble size chunks (rocky and metalic close in icy past snow line) o grew to mountain sized planitesimals accretion.ogg

19 Protoplanets o planitesimals large enough so that gravitational attraction is important o bodies grew up to the size of the moon o past a certain size, gravity is the dominant force the objects become spheres o protoplanets o protoplanets continue to accrete material and grow

20 Gas Giants and Asteroids o ices much more abundant than metals or silicates o ices are also sticky, ~20x more than silcates o agglomeration very rapid o large objects (~15x earth) could capture gas Jupiter forms o Saturn much slower further away; more sparse; grew more slowly Cloud perturbed Protosun Solar globule Planitesimals & Protoplanets Solar Nebula Gas Giants T-Tauri Phase

21 Gas Giants and Asteroids o Jupiter reached 300x earth o Jupiters gravity flings out planitesimals and prevents others from aggregating left over as asteroids

22 T-Tauri Phase o protosun shrunk to few solar radii o 5 million K in centre; surface 5 thousand K o ionises the gases o T-Tauri phase: violent phase, strong magnetic fields (stronger than present) think of the solar activity on steroids o spinning quickly ~ once in 8 days Cloud perturbed Solar globule Planitesimals & Protoplanets Solar Nebula Protosun Gas Giants T-Tauri Phase

23 The Sun during its early T-Tauri phase is still surrounded by a gigantic disc, but the disc s central regions are now swept clear by the whirling magnetic field. Like beads on a wire, blobs of gas leap across this clearing from the disc to the Sun, and fierce flares erupt where the gas strikes the star s toiling surface. [The Story of the Solar System]

24 Outflow o Stellar wind (more furious and with more mass) ~ 200 km/s o wind blasts away excess gas stops Jupiter and Saturns growth o will lose a significant amount of mass o wind relatively brief: ~10,000 years o Sun continues to contract and heat up Feature trillions of km long, Hubble Cloud perturbed Protosun Solar globule Planitesimals & Protoplanets Solar Nebula Gas Giants T-Tauri Phase

25 Seen edge-on from a distance of some 20 billion kilometres, the Solar Nebula appears as a bloated, clumpy pancake. Deflected by this disc and focused by magnetic forces, the Sun s T-Tauri wind forms a bipolar outflow: two jets that extend several lightyears out into the depths of space. [The Story of the Solar System]

26 Ice Giants, Comets and Satelites o Uranus and Neptune took longer to accrete material (further out) o Too late little gas remained after T-Tauri phase o Planitesimals that didn t get swept up got kicked into Kuiper belt and Oort cloud o Around same time satellites where forming around planets in much the same way Cloud perturbed T-Tauri Phase Ice Giants Comets & satelites Main Sequence Terrestrial Planets

27 As the circumplanetary discs continue to feed material into the planets growing at their centres, the rest of the material in the discs lumps together to form the building blocks of satellite systems. In this depiction the four regular moons of Jupiter are emerging from the disc that surrounds that planet. [The Story of the Solar System]

28 Terrestrial Planets Main Sequence o Suns internal temp reaches 15 million K o Fusion starts o Hydrodynamic equilibrium collapse halts o glows hotter yellow o reduced activity T-Tauri Phase Ice Giants Comets & satelites Main Sequence Cloud perturbed

29 An impression of the Sun as we know it, as it has been for the last few billion years. Gone is the angry red colour it had at birth now the Sun glows a slightly hotter yellow. The sunspots are smaller too, the signs of reduced magnetic activity brought about by a slower rotation. [The Story of the Solar System]

30 Terrestrial Planets o silicates and metals a lot less abundant than the ices ( 0.6% of nebula cloud) o Terrestrial planets took a lot longer less material; more destructive environment o too late and not large enough to trap gas Cloud perturbed T-Tauri Phase Ice Giants Comets & satelites Main Sequence Terrestrial Planets

31 Close to the Sun, the terrestrial planets are emerging. Here, the planet Earth still molten is approaching its modern size as it slowly mops up the remaining debris in its vicinity. [The Story of the Solar System]

32 Heavy Bombardment o left over scraps still floating around o shaped planets moons and crusts o crusts often molten planetary differentiation, heavier elements sink; dense cores formed Terrestrial Planets Main Sequence Heavy Bombardment Atmospheres Earliest Fossils

33 Seen from orbit, the primitive Earth and its recently formed Moon endure the bombardment that, 3800 million years later, is still evident on their surfaces especially on the Moon. This image shows the process in its early stages, when the bombardment was at its peak. [The Story of the Solar System]

34 Building Atmospheres o rate of impacts gradually dropped o developed atmospheres by outgassing o icy planitesimals brought water Terrestrial Planets Main Sequence Heavy Bombardment Atmospheres Earliest Fossils

35 As the young Earth endures bombardment, volcanic conduits open up all over the cooling crust and release noxious fumes. These gases cling to the surface, held by gravity, and over billions of years will evolve to form the modern atmosphere. Similar processes shaped the skies of Mars and Venus. [The Story of the Solar System]

36 and some accidents... o e.g. our moon We determined that a Mars-sized impactor would work the best /08/0820_moonimpact.html o Eccentricity of Mercury o Tilt of Uranus o Rotation of Venus reversed o Nearby stars perturb Oort cloud into spherical shape

37 Dynamics our modern era is much quieter... heavens perceived as a precise clockwork An intelligence knowing, at a given instant of time, all forces acting in nature, as well as the momentary positions of all things of which the universe consists, would be able to comprehend the motions of the largest bodies of the world and those of the smallest atoms in one single formula, provided it were sufficiently powerful to subject all data to analysis. To it, nothing would be uncertain; both future and past would be present before its eyes. Laplace clockwork regular or predictable Look at just two effects to illustrate resonances and chaos

38 Resonances when two periods have a simple numerical ratio e.g. Europa:Io 2:1 Ganymede:Europa 2:1 Examples occur throughout solar system

39 Kirkwood gaps in asteroid belt unstable orbital resonances with Jupiter

40 Lorenz Equations (1963) Edward Lorenz simplified model for convection cells in atmosphere

41 Deterministic chaos Impossible to predict details in the long term sensitive dependence on initial conditions The butterfly effect Rapidly lose prediction two close points separate rapidly trajectories get folded back (bounded overall) (imagine small blob of ink in dough that being kneaded) lots of frequencies (sounds noisy) but there no real noise in the dynamics dynamics are just vastly richer than were expected lots of systems: electrical circuits, lasers, chemical reactions, fluids, population dynamics, the weather... Complex behaviour from simple systems

42 The Lorenz Attractor

43 The Rössler attractor

44 Chaos in the Solar System Pluto s orbit shows tell-tale signs of chaos (Sussman & Wisdom 1988) kirkwood gaps Terrestrial Planets... practically stable (no collisions etc) but can t predict angular positions for more than 10s of millions of years still controversy over outer planets: and others... Interesting suggestion: Astronomical engineering: a strategy for modifying planetary orbits

45 The Butterfly Effect [

46 Today Earliest Fossils Timeline Big Bang Birth of Solar System Death of Solar System White Dwarf He burning Planetary Nebula Dinasaurs Extinct Red Giant Subgiant Main Sequence

47 Main Sequence continued o The sun will continue to burn H into He o diameter and brightness slowly increase o In the next billion years 10% increase in luminosity o On Earth polar caps will melt, oceans begin to vanish o in 3.5 billion years 40% more luminous than now o run away greenhouse on Earth o Earth becomes bone dry; surface temp in 100s degrees Big Bang Birth of Solar System Earliest Fossils Today Dinasaurs Extinct Death of Solar System

48 We are 1 billion years in the future, and the Sun is 10 per cent brighter than the star we once knew. Dry river beds, like the one shown here, are the norm rather than the exception, and the planet Earth has become a hot, humid graveyard for trees and large animals. [The Story of the Solar System]

49 Subgiant phase o End of hydrogen in core o not hot enough to fuse He (twice the charge) o core contracts inwards and heats up o Colder H just outside core drawn in and begins to fuse in shell around inert core of He o actual size increases from radiation pressure; surface temperature cools Main Sequence Subgiant Red Giant He burning Planetary Nebula White Dwarf

50 Subgiant phase [The Story of the Solar System]

51 Red Giant Phase o cooling surface layers are more opaque to radiation o surface cools to ~4900C o energy builds up o pressure drives out surface 160x current diameter engulfs mercury o surface cools to ~3100C o massive increase in surface area: sun now 2000x brighter than current Main Sequence Subgiant Red Giant He burning Planetary Nebula White Dwarf

52 Red Giant Phase o Huge stellar wind in few 10s of millions of years sheds 30% of it s mass o planets move outward o core continues to contract and heat up; fusion happens in layer around core [The Story of the Solar System]

53 He burning o core attains 100 million K o He fusion begins violent ignition ( Helium flash ) o core s collapse halts; sun shrinks o hydrodynamic stability once again o He burns up at faster rate o runs out... contracts... pulls in more material... starts up again in shell around inert carbon/oxygen core o fresh energy release expands sun Main Sequence Subgiant Red Giant He burning Planetary Nebula White Dwarf

54

55 Seen from the surface of Jupiter s moon Europa, the red giant Sun appears almost as large in the sky as the giant planet itself. The ice that once covered the moon has now melted, and life perhaps thrives in the ocean that covers the surface. [The Story of the Solar System]

56 Planetary nebula o Only shell burning in sun o He burning very temperature dependent - unstable o huge thermal pulses brought on by fluctuations every 100,000 years or so (~4?) o gradually blows itself apart in expanding clouds of material o naked core s radiation ionises expanding cloud colourful display Main Sequence Subgiant Red Giant He burning Planetary Nebula White Dwarf

57 More than 12 billion years after it formed, the Sun discards its outer layers and surrounds itself in a colourful shroud of nebulosity known as a planetary nebula. The core of the original star can still be seen at the centre of the shell. [The Story of the Solar System]

58 White Dwarf o only compressed core remains 1.5x Earths diameter o but still ½ the suns mass ½ a tonne per cm 3 o mainly carbon and oxygen o no longer fusing but still hot enough to be 35x current brightness o eventually cools (100 billion years?) Main Sequence Subgiant [The Story of the Solar System] Red Giant He burning Planetary Nebula White Dwarf

59 Death of the sun part 5

60 Today Earliest Fossils Big Bang Birth of Solar System Death of Solar System Dinasaurs Extinct