The Solar System - I. Alexei Gilchrist. [The Story of the Solar System]

Transcription

1 The Solar System - I Alexei Gilchrist [The Story of the Solar System]

2 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)

3 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

4 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!

5 Caveat

6 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)

7 Solar System Formation Constraints

8 Some constraints baked earlier...

9 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

10 [The Story of the Solar System]

11 Motional Constraints o Planetary orbits in same plane The Ecliptic is the mean plane of the Earth's orbit around the sun. [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

12 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)

13 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

14 Oort cloud

15 [The Story of the Solar System]

16 Inner solar system as of 1 Oct

17 Inner solar system as of 1 Oct

18 Outer solar system as of 1 Oct

19 Outer solar system as of 1 Oct

20 Distant solar system as of 1 Oct

21 Distant solar system as of 1 Oct

22 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)

23 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

24 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

25 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

26 Motional Constraints o Evidence of frequent and massive impacts Earth Venus Mercury Moon Mars

27 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

28 Composition Constraints

29 [The Story of the Solar System]

30 An obvious constraint? o The planets are close to spheres

31 Composition Constraints o Comets tend to be icy dirty snowball model o Asteroids tend to be rocky and carbon rich

32 Composition Constraints

33

34 Composition Constraints o Particular chemical abundances

35 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