1. the origin of the solar system

2. Our Solar System consists of…
the sun at its center
eight planets, circling around the sun
moons
asteroids
and comets.

3. a review of the origin of matter
the mass of our planet (and you and me) was made w/i about 3 minutes of the Creation Event
then atoms were only H and He
w/i about a billion years stars and galaxies come to be (but no rocky planets at all)

4. the stars is where all the rest of the elements bigger than H and He was made ≤Fe
the elements >Fe were made in supernovae (which is why those elements are rare)
how they all got into a planet and into you is what this lecture is all about

5. the origin of planets
there are two processes to consider here: catastrophes and evolution
catastrophes are sudden “life changing” events (e.g. supernovae, impacts, marriage)
evolution here is just change over a period of time, nothing sudden about it

6. solar nebula which we see all over the place…
we’ll see here that the origin and life of planets is not either/or, but a combo of both
e.g. possibly 2 local supernovae (c) started the condensation of local gas and dust (e) to form a disk of gas and dust called a…
solar nebula which we see all over the place…

7. CONDENSATION/ACCRETION
a cloud of dust and gas collapses due to gravity
it forms a “pizza dough” disk
the new sun blows away excess debris
stuff that has had time to accrete remains as planets

8. Condensation/Accretion
In the beginning, our Solar System was a huge disc of dirt, rocks, dust, gas, ice etc.
In the middle of this disc, the Sun formed due to gravitational pressure until fusion commenced and it began to glow.
At a distance from the center, the planets accreted from these rings of dirt, rock, dust and gas.
The rocky terrestrial planets coalesced closer to the sun out of denser/heavier materials.
The gaseous Jovian giants coalesced further from the sun where it was cold enough for the light elements like hydrogen, helium, and methane to condense.

9. planets orbiting other stars
if solar nebula theory is good, there’d better be extrasolar planets out there
but finding them is a pain: they’re too close to their star, ultra-dim, small, far…
several evidences that they exist: dust and wobbles and light drops…

10. beta Pictoris is the most well known of the dust disk stars
it has a huge cold disk (100x bigger than our solar system) and a hole in the middle, just like our solar system has
planets may have already formed in the hole

11. and here young stars are surrounded by disks of gas and dust
are there new planets being formed here???

12. in Orion we see protostars with dust but no center clearing yet
are planets forming here now?

13. and then there’s wobble
a planet orbiting a star can cause it to wobble just slightly

14. first seen in 51 Pegasus 10+ years ago
have seen 1000s now, but
most are quite large and close to parent star

15. and we have ever-so-slight dimming of star light implying tiny planets are moving in front of a star

16. and we can see tiny Doppler effects from a star’s spectrum implying something small and reflecting star light is moving about up there

17. A survey of the solar system
here we look at the significant characteristics, and clues to how it formed
and we’ll begin to see what a miracle this place is…

18. = almost entirely empty
our solar system is mostly empty space (good)
if our sun were a ping pong ball in this room, Pluto would be a speck of dust on the football field
all the other planets would be sandseed sized at various distances between
= almost entirely empty

19. Size & Distance
Imagine the Solar System being a football field (about 100 m long).
The sun would be a glowing orange in the center.
Pluto would encircle the sun at the edge of the soccer ground, having the size of a dust particle.
The Earth would be 1.3 m away from the “orange“, having the size of a sesame seed.

20. Scaled Down…

21. revolution and rotation
overall we’re pretty darn flat; Mercury is tipped (7˚), Pluto even more (>17˚) (= clues)

22. we all go around the sun in the same direction (= clue)

23. and all spin in the same direction as well (= clue), except…
Venus is spinning backwards(!), Uranus & Pluto on their side
all this helps us understand how they all formed

24. two kinds of planets here is a big clue to how it all came about
there are inner: earthlike - terrestrial - planets…
and the more distant outer: jupiterlike - jovian - planets

25. notice three things following:
the two kinds of planets are distinguished by their location
there is a great difference in mass and density
there are craters everywhere!
all these are clues!

27. clue

28. clue

29. clue

30. space debris only three types: asteroids, comets, meteoroids…
these little guys are some of the remnants of the earliest days

31. asteroids (minor planets) are found mostly between Mars and Jupiter
>20,000 known, but perhaps billions more (can’t be seen)
about 1000 have orbits that take them to inner solar system
many found in other special orbits

33. have actually flown by a few and seen that even they have tiny impact craters in them
were the ones b/t M and J 2.8 AU) the debris of a broken up planet or a planet that never formed?

34. comets are the best known and prettiest of space junk
small nucleus just km across can produce a tail >AU!
as the rocky ice ball comes close to the sun, its ices boil away and dust is released

35. the solar winds push the gases and dust into an enormous tail away from the sun
are they just icy mud-balls???
one way or another they are made of the earliest stuff of the solar system and are a clue to it all

36. here is dust from comets which help give us meteor showers

37. meteors are here and gone (aka shooting stars)
they are just ~sand-sized bits of stuff which vaporize when they hit our atmosphere, lighting up the air as they do
we put on about 40,000 tons a year from this space debris

38. meteor is the streak of light in the atmosphere
meteoroid is the object itself

39. meteorites are those big enough to make it to the ground
almost never does it make it through
but those that do can tell us how old the solar system is!

40. the age of the solar system
we use half-life to help us here
radioactive elements found on Earth, Moon, and meteorites can be examined to see the ratios of parent to daughter
this helps us determine how long these things have been solidified

41. earliest rocks on Earth are ~4.4 billion years old
but Earth is constantly recycling so oldest ones may never be found!!! :(
the Apollo landings found Moon rocks that dated to 4.48 billion years old
Martian rocks that have made it here date to ~4.5 billion years ago

42. meteorites have a wide range as well but the oldest are ~4
meteorites have a wide range as well but the oldest are ~4.6 billion years old
we kind of cheat with the sun’s 5 billion years
we assume it is 5 billion because no rocks date older than that, but!
computer models agree with that age
here’s all the evidence so far…

44. the story of planet building
here astronomers have to take the evidence and solar nebula theory to find out how it all may have happened…

45. the chemical composition of the solar nebula
the composition of the early times can still be seen on the sun’s surface: 73% H, 25% He, 2% heavy elements
we think the planets started by sticking tiny bits of elements and molecules into bigger bits

46. only when a planet gets to about 15 earth-masses does it have enough gravity to steal H and He from the solar nebula
gravitational collapse occurs  increased density, pressure…
J and S did this quickly, U and N more slowly (and U and N were at the outskirts which may mean some of their building blocks were blown away by the sun’s brothers and sisters)
This process actually heats the planet up! (J & S still hot)

47. so what happened with the terrestrials?
they were too small to hold onto lightweight H and He :(
they are dense b/c they formed from the heavier elements
but how did it all happen? a two step process…

48. the condensation of solids
why dense inners, and light outers?
all has to do with the way gases condense in those regions…
near the new hot sun only heavier elements like silicates and metals could condense at all
further out where it’s cooler, lighter elements could condense
way out there water ice, methane, and ammonia could be used as bldg blocks

50. all this is called a condensation sequence
it’s probably even more complicated than this (e.g. the nebula probably cooled as time went by) but however it happened the process was perfect

52. the formation of planetesimals
three processes at work here:
grains of stuff accumulate to bigger things (cms  kms)
bigger clumps (kms) called planetesimals collect into planets
the solar nebula clears up

53. the little guys grow in two ways: condensation and accretion
condensation is like the formation of a snowflake, small stuff runs into bigger stuff and sticks to make bigger stuff

54. bigger things could stick to each other by electrostatic attraction, or polar molecules, or chemical bonding, or other forces such as gravity!
like building a snowman from the snowflakes
called accretion

55. a
big accreted guys could be brought to a growing thin disk and concentrate there; gas and tiny dust particles couldn’t
speeds up planet-making!

56. see in this meteorite all the tiny grains of stuff all stuck together

57. see in this meteorite all the bigger bits of stuff all stuck together

58. new computer models show that this disk is unstable, that little eddies would have formed
this further concentrates stuff; now we have particles growing from cm’s  tiny planets…

60. the growth of protoplanets
thankfully, all the clumps of stuff is moving in the same direction so they don’t annihilate each other
in fact, this helps them grow bigger!
chemical adhesive forces and electrostatic cling still let this stuff hold on to each other, to be sure, but -
gravity plays a huge role in holding it all together

61. and now even small impacts might help:
by getting smacked, a little layer of dust might form
the layer of dust could act like a trap
and getting bigger means more gravity means better able to hold onto a very thin atmosphere
now can be considered a protoplanet

62. now this big homogeneous ball begins to heat up (b/c of gravitational pressure and radioactive decay)
as it melts, the heavy stuff (Ni & Fe) falls toward center; lighter silicates float to top
= differentiation
the heat causes outgassing; the driving out of gases trapped in rocks
makes early atmosphere!!!

63. a slight variation says this:
as the solar nebula cooled, the metals condensed first
as the solar nebula cooled more, the silicates could condense onto the metal-based planets

64. an even better theory says the planets formed quickly and that as they condensed the heat of condensation helped differentiate the planetary layers as they formed
which actually happened?
we don’t know.

70. way out there in the extreme cold the jovians quickly swept up gases as part of their makeup
they probably formed pretty quickly (< 10 million years)
[recent computer models show jovian types can form in just a couple revolutions! only hundreds of years!]
the terrestrials took ~30 million years
all over within 100 million years

71. explaining the characteristics of the solar system
let’s look at the clues and see how they are explained…
whole solar system disk shaped?
b/c solar nebulae do that (gravity & centrifugation)
sun and planets rotate and revolve in same direction?
b/c all formed from same disk
all planets on same plane?
b/c the solar nebula collapsed into a disk

72. what about Venus & Uranus & Pluto?
catastrophes! planet collision, though rare, are possible and probably knocked Venus and Uranus around
even we were probably hit by another planet
(--> moon)

73. why terrestrial/jovian difference?
the condensation process (inside and hot condense only metals/silicates; outside and cold can condense water and other gases to build planets)
and more material means more planet

74. grow to ~15 earth-massee and you get to vacuum up gases in the solar-nebula (jovians)
also, Jupiter’s gravity was probably responsible for preventing the formation of a planet between it and Mars
those planetesimals are still there as the asteroid belt

75. comets are the icy planetesimals left-overs from the outer solar system
the multitude of moons could have been formed from mini solar nebs around the planets, or…
may have been captured space debris

76. the great distances of the jovians make it easier for them to hold onto their ring of debris
and their ages all agree with a common birth date
and the asteroids, comets, and meteorites are explained as left-overs from the solar nebula

77. clearing the nebula

78. look up in the night sky and it’s pretty clear!
what happened to the solar nebula?
it vanished when sun was young; but how?

79. radiation pressure!
when the sun got luminous enough, its radiation’s interaction with matter could literally push tiny specks and atoms right out of solar system

80. solar wind!!!
the flow of ionized stuff from the sun, the sun’s breeze, pushes the dust and gas out, as well

81. vacuum effect:
the planets, as they grew, swept up the bigger stuff with their gravity
look at the surfaces of the planets and satellites and asteroids
there are millions of impacts

82. and most of them date from ~4 billion years ago
this was the time of heavy bombardment
we still get hit but not like the rain of old

83. ejection
little stuff can whip around big guys and be tossed from the solar system
jovians were very effective here (and still are)

84. the wonderfully orchestrated set of events that led from the Creation Event to the formation of the solar system can be fairly well explained