Molecules in space couldn't do much unless surrounding starsi.
Our solar systems started with a flattening disk that led to fusion.ii.
99% of the matter is the sun, the 1% is the rest of the solar systemiii.
Outer gassy planets contain 99% of the rest of the materialiv.
Accretion: material gathers together through collisions and materials orbiting then
Contains great diversity of materials1.
Universe is getting more complex, diverse, and intersting2.
4th threshold: formation of earth and solar systemi.
Big History Project: How did the Earth and Solar System form?I.
How did the Solar System Form?
Hist 2720: Big History
Originally proposed by Immanuel Kant and Pierre-Simon de Laplace two centuries ago•
Interstellar gas and dust gathers and collapses under its own gravity•
As it collapses, it gathers angular momentum, spins faster and flattens out•
Planets gather in orbiting disk of dust (protoplanetary disk) around large central sun•
Collapsing Cloud Model
No direct evidence, just a reasonable hypothesis
Why so little angular momentum in the sun?•
Some initial problems…
Hard to see how else the sun could have captured planets•
Captured objects would orbit in different planes and direction○
Or why all the planets orbit in the same direction and same plane•
…but no good alternatives
Asteroids and meteors as leftovers from early solar system, haven't gone through tectonics
that ruin the early structure
Composition of meteorites helps reveal process of accretion•
New Evidence: Space Rocks
Same number of protons, different number of neutrons•
Stable isotopes reveal provenance of matter - don't spontaneously decay over time; come
from same place/process
Radioactive isotopes reveal age through radiometric dating - decay at regular periods over
Solar system 4.55 billion years old•
New Evidence: Isotopes
Determine composition of other planets, moons, and asteroids•
Understand geology and change in Mars and Venus•
New Evidence: Extraplanetary Missions (landers and space craft)
Dust clumps in pebbles shown through experiments•
Planetesimals gather matter and become planets•
But how do we get from pebbles to planetesimals?
New Evidence: Experiments and Models of Accretion
Sunday, January 28, 2018 10:29 PM