[The Story of the Solar System]
The Solar System -
IAlexei Gilchrist
Some resources•
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)
Constraints
o The clues –
where, what
and when (motion, composition, and age)
o Rather like a crime scene –we are left with a set of clues
o Each clue gives a constraint –
any explanation has to fit within thisconstraint
o what makes a good constraint?... look for patterns, general features
-
This lecture: the crime scene-
Next lecture: we accuse someone
o We don’t yet have enoughconstraints –
many models couldhave led to the Solar System
Caveat
o May turn out that our solar system happened by a very improbable mechanism and not the way we think at all(so some constraints may be bogus)
o We only have one solar system ... science needs to testo We can look for internal consistency between the sciences and
the models (test parts of the model, e.g. fusion mechanisms),... and we can look elsewhere in the universe
o Starting to discover other planets ... they don’t fit the models !
o current observationtechniques give a verybiased sample though
like estimating heights in a maze
o Great time to watchscience in action!
Caveat
On to the crime scene
You’ve sat through 9 weeks of lectures ...
e.g. All the planets end up moving pretty much in circles(any model would have to end up with this feature)
What constraints would you put on a model of the origin of the solar system?
Motional Constraintso Planetary orbits are nearly circular
Mercury 0.21Venus 0.01Earth 0.02Mars 0.09
Jupiter 0.05Saturn 0.06Uranus 0.05
Neptune 0.01
Orbit Eccentricity
http://www.nineplanets.org/data.html
[The Story of the Solar System]
Motional Constraints
http://www.allaboutspace.com/subjects/astronomy/solarsystem/ecliptic.shtml
The Ecliptic is the mean plane of the Earth's orbit around the sun.
Mercury 7.0Venus 3.4Earth 0Mars 1.9
Jupiter 1.3Saturn 2.5Uranus 0.8
Neptune 1.8
Degrees of Inclination
http://www.nineplanets.org/data.html
o Planetary orbits in same plane
[The Story of the Solar System]
Motional Constraintso Asteroids mainly occupy 2 locations:
- Asteroid belt between Mars and Jupiter
-
Trojan asteroidsin same orbit
as Jupiter
http://en.wikipedia.org/wiki/Trojan_asteroid
(Roughly disk shaped)
(At L3 & L4 points)
Motional Constraints
o
(1980) Realised
most short period comets couldn’t originate from captured long period comets –
had to come from closer. Suggested trans-Neptunian belt of icy comets
o
(1992) First trans-Neptunian object found (QB1); ~250km diameter
o
Now know of >400 such objects; largest KX76 is 1300 km acrosso
Exact extent of Kuiper
belt not known; the objects are dark, small and a long way away –
very difficult to detect
o Comets seem to occupy 2 locations:
-
Kuiper
belt
-
past Neptune (trans-Neptunian objects) ... may contain 100s of millions of objects
NB distiction
betweenasteroids and comets not that clear cut
-
Oort
cloud
–
indirect evidence ... suspect trillions of objectsspherically distributed
Kuiper
belt
Oort cloud
http://en.wikipedia.org/wiki/90377_Sedna
[The Story of the Solar System]
Inner solar system as of 1 Oct 2008
http://ssd.jpl.nasa.gov/?ss_inner
Inner solar system as of 1 Oct 2008
http://ssd.jpl.nasa.gov/?ss_inner
Outer solar system as of 1 Oct 2008
http://ssd.jpl.nasa.gov/?ss_outer
Outer solar system as of 1 Oct 2008
http://ssd.jpl.nasa.gov/?ss_outer
Distant solar system as of 1 Oct 2008
http://ssd.jpl.nasa.gov/?ss_distant
Distant solar system as of 1 Oct 2008
http://ssd.jpl.nasa.gov/?ss_distant
Motional Constraintso All the planets revolve around in same direction
Uran
us
Neptu
ne
Satur
n
Pluto
Jupite
r
Mars
anticlockwiseViewed from ‘above’
(N)
Motional Constraints
Mercury 0° Venus 177° Earth 23° Mars 25°
Jupiter 3° Saturn 27° Uranus 98° Neptune 30°
http://www.lpi.usra.edu/education/resources/s_system/solar_sys_formation.ppt
http://www.nineplanets.org/data2.html
o most planets (and sun) also rotate in same direction
Motional Constraints
o The planetary regular satellites- move in nearly circular orbits-
have the same orbital direction
as the planets spins
o The planetary irregular satellites
- Tend to be smaller- large orbits- possibly significant eccentricity- possibly significant inclination
Motional Constraints
o The sun is spinning way too slow
Sun has 99.9% of mass of solar systembut only 1% or less of the angular momentum
Angular momentum is conserved
before after
Motional Constraints
Mercury Venus
Earth
o Evidence of frequent and massive impacts
MoonMars
Composition Constraintso 3 classes of planets (not to scale)
Gas giants Ice GiantsTerrestrial
o smallo rocky & metalic
o largesto mostly H & He
(same as sun)
o intermediate sizeo ices
http://atropos.as.arizona.edu/aiz/teaching/nats102/mario/solar_system.html
http://www.mso.anu.edu.au/~josan/filesfordown/PPV-2005.pdf
Composition Constraints
[The Story of the Solar System]
An obvious constraint?
o The planets are close to spheres
Composition Constraintso Comets tend to be icy
o Asteroids tend to be rocky and carbon rich
dirtysnowballmodel
Composition Constraints
Composition Constraints
http://en.wikipedia.org/wiki/Image:SolarSystemAbundances.jpg
o Particular chemical abundances
Age Constraints
o Earliest fossils are around 3.5 billion years old
o Some rocks on earths surface 3.8 billion years old
o primitive meteorites are about 4.5 billion years old
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