[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