2Our Solar System consists of… the sun at its centereight planets, circling around the sunmoonsasteroidsand comets.
3a 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 Eventthen atoms were only H and Hew/i about a billion years stars and galaxies come to be (but no rocky planets at all)
4the 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
5the origin of planetsthere are two processes to consider here: catastrophes and evolutioncatastrophes are sudden “life changing” events (e.g. supernovae, impacts, marriage)evolution here is just change over a period of time, nothing sudden about it
6solar 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 bothe.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…
7CONDENSATION/ACCRETION a cloud of dust and gas collapses due to gravityit forms a “pizza dough” diskthe new sun blows away excess debrisstuff that has had time to accrete remains as planets
8Condensation/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.
9planets orbiting other stars if solar nebula theory is good, there’d better be extrasolar planets out therebut 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…
10beta 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 hasplanets may have already formed in the hole
11and here young stars are surrounded by disks of gas and dust are there new planets being formed here???
12in Orion we see protostars with dust but no center clearing yet are planets forming here now?
13and then there’s wobble a planet orbiting a star can cause it to wobble just slightly
14first seen in 51 Pegasus 10+ years ago have seen 1000s now, butmost are quite large and close to parent star
15and we have ever-so-slight dimming of star light implying tiny planets are moving in front of a star
16and we can see tiny Doppler effects from a star’s spectrum implying something small and reflecting star light is moving about up there
17A survey of the solar system here we look at the significant characteristics, and clues to how it formedand 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 fieldall the other planets would be sandseed sized at various distances between= almost entirely empty
19Size & DistanceImagine 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.
30space debris only three types: asteroids, comets, meteoroids… these little guys are some of the remnants of the earliest days
31asteroids (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 systemmany found in other special orbits
33have 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?
34comets 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
35the 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
36here is dust from comets which help give us meteor showers
37meteors 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 dowe put on about 40,000 tons a year from this space debris
38meteor is the streak of light in the atmosphere meteoroid is the object itself
39meteorites are those big enough to make it to the ground almost never does it make it throughbut those that do can tell us how old the solar system is!
40the age of the solar system we use half-life to help us hereradioactive elements found on Earth, Moon, and meteorites can be examined to see the ratios of parent to daughterthis helps us determine how long these things have been solidified
41earliest 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 oldMartian rocks that have made it here date to ~4.5 billion years ago
42meteorites 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 oldwe kind of cheat with the sun’s 5 billion yearswe assume it is 5 billion because no rocks date older than that, but!computer models agree with that agehere’s all the evidence so far…
44the story of planet building here astronomers have to take the evidence and solar nebula theory to find out how it all may have happened…
45the 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 elementswe think the planets started by sticking tiny bits of elements and molecules into bigger bits
46only when a planet gets to about 15 earth-masses does it have enough gravity to steal H and He from the solar nebulagravitational 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)
47so 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 elementsbut how did it all happen? a two step process…
48the 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 allfurther out where it’s cooler, lighter elements could condenseway out there water ice, methane, and ammonia could be used as bldg blocks
52the formation of planetesimals three processes at work here:grains of stuff accumulate to bigger things (cms kms)bigger clumps (kms) called planetesimals collect into planetsthe solar nebula clears up
53the 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
54bigger 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 snowflakescalled accretion
55abig accreted guys could be brought to a growing thin disk and concentrate there; gas and tiny dust particles couldn’tspeeds up planet-making!
56see in this meteorite all the tiny grains of stuff all stuck together
57see in this meteorite all the bigger bits of stuff all stuck together
58new 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…
60the growth of protoplanets thankfully, all the clumps of stuff is moving in the same direction so they don’t annihilate each otherin 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
61and now even small impacts might help: by getting smacked, a little layer of dust might formthe layer of dust could act like a trapand getting bigger means more gravity means better able to hold onto a very thin atmospherenow can be considered a protoplanet
62now 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= differentiationthe heat causes outgassing; the driving out of gases trapped in rocksmakes early atmosphere!!!
63a slight variation says this: as the solar nebula cooled, the metals condensed firstas the solar nebula cooled more, the silicates could condense onto the metal-based planets
64an even better theory says the planets formed quickly and that as they condensed the heat of condensation helped differentiate the planetary layers as they formedwhich actually happened?we don’t know.
70way 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 yearsall over within 100 million years
71explaining 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 diskall planets on same plane?b/c the solar nebula collapsed into a disk
72what about Venus & Uranus & Pluto? catastrophes! planet collision, though rare, are possible and probably knocked Venus and Uranus aroundeven we were probably hit by another planet(--> moon)
73why 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
74grow 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 Marsthose planetesimals are still there as the asteroid belt
75comets 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
76the 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 dateand the asteroids, comets, and meteorites are explained as left-overs from the solar nebula