Phys 1830: Lecture 19

1. Phys 1830: Lecture 19 (Image unknown origin) • Second Term Test is coming up Nov 1. • Review is now posted on our class website. • Previous Class: • Visualization: Computer Simulations • Planetary Systems • This Class: • Solar System • Solar System Formation • Next Class: • Solar System Formation continued • Tour of the Solar System

2. Public Talk March 13th – Neil deGrasse Tyson DREAM BIG! (A Student Life event) Email me today with your interests or visit me Monday to discuss. • Image-making workshop  exhibition in “campo” • produce a display of space milestones – needs a coordinator and volunteers

3. Planetary Systems • Simulations start with disks filled with gas and dust. • Observations motivate this initial configuration.

4. Planetary Systems & Disks -- Solar System: Looking towards the Sun Looking towards Jupiter • The orbits of the 8 classical planets also indicate that our solar system evolved out of a disk. • The planets’ orbits lay in a narrow plane. Mercury deviates the largest (with only a 7 degree tilt). • They all orbit in the same direction.

5. Planetary Systems Eagle Nebula (M16) • Assumption that planets form in disks was motivated by observations. • Is the assumption that the disk is initially very gaseous a good one?

6. Planetary Systems • Molecular Cloud with “fingers” protruding. • Evaporating Gaseous Globules = EGGs at finger tips. • Each about the size of our solar system.

7. Planetary Systems: Bok Globules in Carina Nebula • Surrounding molecular gas cloud photoevaporates leaving denser globules of rotating gas. • Material in a globule falls towards the centre via gravity. • Simultaneously, due to conservation of angular momentum, a disk consisting mainly of gas and dust forms --> proplyds.

8. Planetary Systems • Animation from Swinburne University, Centre for Astronomy and Supercomputing. • Assumption that gas dominates the initial conditions is also founded on observations. • The central condensation will become a star.

9. Planetary System Formation - Observations: • Orion is an example of a dusty, gas cloud forming planetary systems. • Distance is 1,500 ly (460 parsecs). • Proplyds and Bok Globules inform the simulations of star and planet formation.

10. Visualizations: Simulations of Planetary Systems Observations Animation based on Simulation • Observations of a planetary system with a ring and planets can be explained by a simulation. • Planetary disk simulations use: • gravity between particles, • gravity between particles and the protostar, • hydrodynamical forces • Note that the planets have cleared their orbits in the simulations.

11. Visualizations: Simulations • Two assumptions for modelling the formation of planets are: • A cloud composed of rocks collapses. This forms a disk. (The biggest rocks are the planets.) • A cloud composed mainly of gas collapses. This forms a disk. (Planets form within this disk.) • Chunks of gas tear off from molecular clouds. Photo-evaporation exposes the planets buried inside these Bok Globules.

12. Extra-solar planets == Exoplanets • More on this after we study our own Solar System

13. Solar System • The assumptions in the models of the formation of planetary systems are reasonable since supported by observations of other “solar systems”: • Gas dominates • Disks form • The models also have to match features of our own Solar System. • Why do all the planets orbit in a plane? • Why do they orbit in the same direction? • Why are some planets gaseous and others not?

14. Solar System Overview: Planet Definitions • Classical Planet • Orbits the sun. • Massive enough that is own gravity has caused its shape to be nearly spherical. • It has “cleared the neighbourhood” around its orbit of other bodies. • i.e. either by colliding with (sweeping up) the debris in the disk or by gravitationally kicking the debris out of its path (slingshot effect).

15. Solar System Overview: Planet Definitions • Examples: • Pluto • Eris (1.3 * Pluto’s mass) • Ceres (in the asteroid belt) • Dwarf Planet • Orbits the sun. • Massive enough that is own gravity has caused its shape to be spherical. • Is not a satellite of another body. (Has not cleared its neighbourhood.) Objects at Neptune and beyond are called Trans-Neptune Objects (TNO) and those TNO that are similar to Pluto are called plutoids.

16. Solar System Overview: What does the class already know about the classical planets? • Divide up into 8 teams – one team per planet. • A note-taker per team. • 2 judges. • Can use textbooks, computers (if you downloaded stuff), pictures, and, most importantly, humour! Presentations are a maximum of 5 min. When other people are presenting, take notes since we don’t have a textbook.

17. Solar System Overview: What does the class already know about the classical planets? • For each planet: • revolve & rotate in the same direction as other planets? • primarily composed of rock or of gas? # Earth Masses, # Earth radii • small or large? (i.e. closer to Earth size or Jupiter size?) • in outer region or inner region of solar system? • hot or cold? surface T in Kelvin • Lots of moons? • Any other details are welcome  (eg. Does it have rings? B field?) Note about T: -273 C = 0 K

18. Solar System Overview: Material for our contest! • The first 8 are planets. • Note the second column.

19. Solar System Overview • Keplerian Rotation Curve.

20. Solar System Overview • The density in kg/m • 1000 for water; anything less than this floats in water. • 2000-3000 for rocks and 8000 for iron • Note the 2nd last column. Note the density of Earth. • Which planets have densities like rocks/iron? Float on water? 3

21. Solar System Overview This classical planet would float if there was a big enough bathtub to put it in. • Pluto, because it is the smallest planet. • Earth, because it has so much water anyway. • Europa, because it is icey. • Saturn, because its density is less than water.

22. Solar System Overview: • How do we know what we know about our solar system? • Distances • Diameters • Masses • Densities

23. Solar System Overview Orbits of planets are nearly circular  use Newton’s Laws for a circular orbit of radius “r”. M is mass of sun. Recall: • Distances from the Sun: • Radar • Kepler’s Third Law (empirical) Rearrange: Need velocity to get radius.

24. Solar System Overview: Distances • Velocity of Planets: • v = distance/time Distance: The length of the path of the orbit is the circumference of a circle. Time: The time to travel the full orbit is the Period “P”. Substitute in for distance and time:

25. Solar System Overview: Distances • Substitute v squared into the equation for radius: Just need to observe the Period to get the distance!

26. Solar System Overview: We have the distance! -- for ellipses Observe the Period! Using a in au and P in Earth years. Orbit of planet • Kepler’s Third Law sun a

27. Solar System Overview • Keplerian Rotation Curve.

28. Solar System Overview Linear diameter angular diameter --------------------- = ----------------------- 2 pi * Distance 360 degrees 2 pi * Distance linear diameter = --------------------- * angular diameter 360 degrees 2. Diameters - from lecture 4 We can get the distance between a planet and Earth by using step 1 to get its distance to the sun and using geometry to get the distance to the Earth. (In contemporary times, we can use radar.) Then we just need to measure the angular diameter and we have the size of the planet.

29. Solar System Overview Rearrange:  use step 2 procedure. 3. Masses Do this with a satellite around the planet. For example the moon around the Earth. Then “r” is the Earth-Moon distance and M is the mass of the Earth. Velocity v is determined from the Period of the moon’s orbit (e.g. 1/12 of a year).

30. Solar System Overview And for a sphere: (Where R is radius.) So  Mass from step 3. 4. Density • diameter • from step 2.

31. Solar System Overview: That is how do we know some of these values

32. Solar System Overview: What does the class already know about the classical planets? Mass and Radius only relative to Earth. Temperature only in Kelvin. • For each planet: • Does it revolve in the same direction as the other planets? • Is it primarily composed of rock or of gas? • Is it small or large? (i.e. closer to Earth size or Jupiter size?) • Is it in the outer region or inner region of the solar system? • Is it hot or cold? • Lots of moons or few? • Any other details are welcome  (eg. Does it have rings?) B field?

33. Mercury Messenger: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

34. Venus: Venus Express/European Space Agency Ultraviolet Image

35. Earth

36. Mars Mars Express/European Space Agency Hebes Chasma

37. Jupiter New Horizons/NASA IR image.

38. Saturn Cassini/NASA

39. Uranus Voyager2/NASA “True” Colour False Colour

40. Neptune Voyager2/NASA