[The Story of the Solar System]
The Solar System -
II
Some resources
o Section 13.3 of Voyages (references and links at end)
o References noted in these slides
o The Story of the Solar System, M Garlick, (Cambridge Uni. Press, 2002)
Timeline
Today
Big Bang Earlies
t Foss ils
Birth of Solar System Dinasaurs Death of Solar System
Extin ct Cloud pertu rbed T-Ta uri P hase Ice Gi ants Come ts & s ateli tes Terre strial Plan ets Main Sequ ence Heavy Bombardment Atmosp heres Earlies t Fossil s Main Sequence Terrestrial Planets
Timeline
Pla nit esim als & P rot opla nets Cloud pertu rbed T-Ta uri P hase Ice Gi ants Come ts & s ateli tes Terre strial Plan ets Main Sequ ence Cloud pert urbe d So lar glo bule Pro tosun Gas Gian ts T-T aur i Ph ase So lar N eb ulaGiant Molecular Cloud
o About 50-100 light years acrosso more than a million times the suns mass
o mostly (73%) molecular Hydrogen; rest Helium; traces of other stuff
o not very dense (better than a first-class vacuum)
o very cold (~ -250C)
o Something triggered it to start
collapsing (supernova – shockwaves ?)
Today
Big Bang Earlies
t Foss ils
Birth of Solar System Dinasaurs Death of Solar System
Extin ct
Spitzer telescope
spitzer.ogg
Nucleosynthesis
From: http://www.astro.wesleyan.edu/~bill/courses/astr231/wes_only/element_abundances.pdf
Need an injection of heavier elements from elsewhere
[The Story of the Solar System][The Story of the Solar System]
“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.”
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 Pla
nit esim als & P rot opla nets Cloud pert urbe d So lar glo bule Pro tosun Gas Gian ts T-T aur i Ph ase So lar N eb ula
[The Story of the Solar System]
“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.”
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) Planit
esim als & P rot opla nets Cloud pert urbe d So lar glo bule Pro tosun Gas Gian ts T-T aur i Ph ase So lar N eb ula
Origin of spinning
Angular momentum is conserved
[The Story of the Solar System]
“The protosunas 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 protosunat an advanced stage, is now hot enough to glow, its temperature around a few thousand degrees.”
Solar Nebula
o Flattens due to rotation - turbulent pancake of gas
surround core
o core out to mercury; disc 100-200 AU
o temp ~2000K in core begins to shine
o most of the globule consumed
Pla nit esim als & P rot opla nets Cloud pert urbe d So lar glo bule Pro tosun Gas Gian ts T-T aur i Ph ase So lar N eb ula
[The Story of the Solar System]
“The Solar Nebula, a swirling pancake of gas and dust, surrounds the newly forming star known as the Sun. Later, planets will form there.”
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 Pla nit esim als & P rot opla nets Cloud pert urbe d So lar glo bule Pro tosun Gas Gian ts T-T aur i Ph ase So lar N eb ula
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
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”
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”
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
Pla nit esim als& Pro top lan ets Cloud pert urbe d So lar glo bule Pro tosun Gas Gian ts T-T aur i Ph ase So lar N eb ula
Gas Giants and Asteroids
o Jupiter reached 300x earth
o Jupiters gravity flings out planitesimals and prevents
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 Planitesim
als & P rot opla nets Cloud pert urbe d So lar glo bule Pro tosun Gas Gian ts T-T aur i Ph ase So lar N eb ula
[The Story of the Solar System]
“The Sun during its early T-Tauriphase 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.”
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
Pla nit esim als& Pro top lan ets Cloud pert urbe d So lar glo bule Pro tosun Gas Gian ts T-T aur i Ph ase So lar N eb ula Feature trillions of km long, Hubble
[The Story of the Solar System]
“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-Tauriwind forms a bipolar outflow: two jets that extend several lightyearsout into the depths of space.”
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 pertu rbed T-Ta uri P hase Ice Gi ants Come ts & s ateli tes Terre strial Plan ets Main Sequ ence
[The Story of the Solar System]
“As the circumplanetarydiscs 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.”
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 Cloud pertu rbed T-Ta uri P hase Ice Gi ants Come ts & s ateli tes Terre strial Plan ets Main Sequ ence
[The Story of the Solar System]
“An impression of the Sun as we know it, as it has been for the last few billion years. Gone is the angry red colourit 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.”
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 pertu rbed T-Ta uri P hase Ice Gi ants Come ts & s ateli tes Terre strial Plan ets Main Sequ ence
“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.”
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
Heavy Bombardment Atmosp heres Earlies t Fossil s Main Sequence Terrestrial Planets
[The Story of the Solar System]
“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.”
Building Atmospheres
o rate of impacts gradually dropped
o developed atmospheres by outgassing
o icy planitesimals brought water
Heavy Bombardment Atmosp heres Earlies t Fossil s Main Sequence Terrestrial Planets
[The Story of the Solar System]
“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.”
and some accidents...
“We determined that a Mars-sized impactor would work the best”
http://news.nationalgeographic.com/news/ 2001/08/0820_moonimpact.html o e.g. our moon
o Eccentricity of Mercury o Tilt of Uranus
o Nearby stars perturb
Oort cloud into spherical
shape
o Rotation of Venus reversed
Dynamics
clockwork regular or predictable our modern era is much quieter ...
heavens perceived as a precise clockwork
Look at just two effects to illustrate – resonances and chaos “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
Resonances
when two periods have a simple numerical ratio e.g. Europa:Io 2:1
Ganymede:Europa 2:1
http://www.fortunecity.com/emachines/e11/86/solarsys.html
http://en.wikipedia.org/wiki/Orbital_resonance
Kirkwood gaps in asteroid belt
unstable orbital resonances with Jupiter
Lorenz Equations
(1963) Edward Lorenzsimplified model for convection cells in atmosphere
Deterministic chaos
Impossible to predict details in the long term “sensitive dependence on initial conditions”
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 ...
two close points
separate rapidly trajectories get folded back(bounded overall)
Rapidly lose prediction
(imagine small blob of ink in dough that being kneaded)
The butterfly effect
Complex behaviour from simple systems
Chaos in the Solar System
kirkwood gaps Pluto’s orbit shows tell-tale signs
of chaos (Sussman & Wisdom 1988) 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: http://arxiv.org/abs/astro-ph/0702179 and others ...
Interesting suggestion: http://arxiv.org/abs/astro-ph/0102126 “Astronomical engineering: a
strategy for modifying planetary orbits”
[http://xkcd.com/378/]
Timeline
Today
Big Bang Earlies
t Foss ils
Birth of Solar System Dinasaurs Death of Solar System
Extin ct White Dwarf Red Gi ant Subgi ant Main S equenc e He bu rning Planet ary Ne bula
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
Today
Big Bang Earlies
t Foss ils
Birth of Solar System Dinasaurs Death of Solar System
Extin ct
“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.”
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 White Dwarf Red Gi ant Subgi ant Main S equenc e He bu rning Planet ary Ne bula
Subgiant
phase
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
White Dwarf Red Gi ant Subgi ant Main S equenc e He bu rning Planet ary Ne bula
[The Story of the Solar System]
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
He burning
White Dwarf Red Gi ant Subgi ant Main S equenc e He bu rning Planet ary Ne bulao 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
[The Story of the Solar System]
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.
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 White Dwarf Red Gi ant Subgi ant Main S equenc e He bu rning Planet ary Ne bula
“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
White Dwarf
o only compressed core remains – 1.5x Earths diameter
o but still ½ the suns mass – ½ a tonne per cm3
o mainly carbon and oxygen
o no longer fusing but still hot enough to be 35x
current brightness o eventually cools (100 billion years?) White Dwarf Red Gi ant Subgi ant Main S equenc e He bu rning Planet ary Ne bula [The Story of the Solar System]
Death of the sun part 5
Today
Big Bang Earlies
t Foss ils
Birth of Solar System Dinasaurs Death of Solar System
Extin ct
