The Solar System - I Alexei Gilchrist [The Story of the Solar System]
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 Rather like a crime scene we are left with a set of clues o The clues where, what and when (motion, composition, and age) o Each clue gives a constraint any explanation has to fit within this constraint o what makes a good constraint?... look for patterns, general features o We don t yet have enough constraints many models could have led to the Solar System - This lecture: the crime scene - Next lecture: we accuse someone
Caveat o We only have one solar system... science needs to test o 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 observation techniques give a very biased sample though like estimating heights in a maze 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 Great time to watch science in action!
Caveat
On to the crime scene You ve sat through 9 weeks of lectures... What constraints would you put on a model of the origin of the solar system? e.g. All the planets end up moving pretty much in circles (any model would have to end up with this feature)
Solar System Formation Constraints
Some constraints baked earlier...
Motional Constraints o Planetary orbits are nearly circular Orbit Eccentricity Mercury 0.21 Venus 0.01 Earth 0.02 Mars 0.09 Jupiter 0.05 Saturn 0.06 Uranus 0.05 Neptune 0.01 http://www.nineplanets.org/data.html
[The Story of the Solar System]
Motional Constraints o Planetary orbits in same plane The Ecliptic is the mean plane of the Earth's orbit around the sun. http://www.allaboutspace.com/subjects/astronomy/solarsystem/ecliptic.shtml [The Story of the Solar System] Degrees of Inclination Mercury 7.0 Venus 3.4 Earth 0 Mars 1.9 Jupiter 1.3 Saturn 2.5 Uranus 0.8 Neptune 1.8 http://www.nineplanets.org/data.html
Motional Constraints o Asteroids mainly occupy 2 locations: - Asteroid belt between Mars and Jupiter (Roughly disk shaped) - Trojan asteroids in same orbit as Jupiter (At L4 & L5 points) http://en.wikipedia.org/wiki/trojan_asteroid
Motional Constraints o Comets seem to occupy 2 locations: NB distiction between asteroids and comets not that clear cut - Oort cloud indirect evidence... suspect trillions of objects spherically distributed - Kuiper belt - past Neptune (trans-neptunian objects)... may contain 100s of millions of objects Kuiper belt 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 across o Exact extent of Kuiper belt not known; the objects are dark, small and a long way away very difficult to detect
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 Constraints o All the planets revolve around in same direction rn Ne pt u Plu to ne Ur an us er it p Ju Sa tu M ar s anticlockwise Viewed from above (N)
Motional Constraints o most planets (and sun) also rotate in same direction Mercury 0 Mars 25 Jupiter 3 30 Venus 177 Saturn 27 Earth 23 Uranus 98 Neptune http://www.lpi.usra.edu/education/resources/s_system/solar_sys_formation.ppt http://www.nineplanets.org/data2.html
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 system but only 1% or less of the angular momentum Angular momentum is conserved before after
Motional Constraints o Evidence of frequent and massive impacts Earth Venus Mercury Moon Mars
Composition Constraints o 3 classes of planets Terrestrial (not to scale) Gas giants o largest o small o rocky & metalic o mostly H & He (same as sun) Ice Giants o intermediate size o ices
Composition Constraints http://www.mso.anu.edu.au/~josan/filesfordown/ppv-2005.pdf http://atropos.as.arizona.edu/aiz/teaching/nats102/mario/solar_system.html
[The Story of the Solar System]
An obvious constraint? o The planets are close to spheres
Composition Constraints o Comets tend to be icy dirty snowball model o Asteroids tend to be rocky and carbon rich
Composition Constraints
Composition Constraints o Particular chemical abundances http://en.wikipedia.org/wiki/image:solarsystemabundances.jpg
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