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Phys 1830: Lecture 22 summary (Image unknown origin) Recall column • • test marks posted outside my office other marks posted as available • • • Previous Class: – Visualization: Computer Simulations – Planetary Systems This Class: Took up term test #2 – Solar System Next Class: • Solar System Formation • Tour of the Solar System Solar System Overview: Planet Definitions summary Recall column A. Classical Planet 1. Orbits the sun. 2. Massive enough that is own gravity has caused its shape to be nearly spherical. 3. 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). Solar System Overview: Planet Definitions summary Recall column A. Dwarf Planet 1. Orbits the sun. 2. Massive enough that is own gravity has caused its shape to be spherical. 3. Is not a satellite of another body. (Has not cleared its Examples: neighbourhood.) • Pluto • Eris (1.3 * Pluto’s mass) • Ceres (in the asteroid belt) Objects at Neptune and beyond are called TransNeptune Objects (TNO) and those TNO that are similar to Pluto are called plutoids. Solar System Overview: What does the class already know about the classical planets? Recall column Note about T: -273 C = 0 K summary • 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?) Solar System Overview: Material for our contest! Recall column • The first 8 are planets. • Note the second column. summary Solar System Overview Recall column • Keplerian Rotation Curve. summary Solar System Overview summary Recall column • The density in kg/m3 – 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? Solar System Overview Recall column summary This classical planet would float if there was a big enough bathtub to put it in. a) Pluto, because it is the smallest planet. b) Earth, because it has so much water anyway. c) Europa, because it is icey. d) Saturn, because its density is less than water. Solar System Overview: Recall column • How do we know what we know about our solar system? 1. Distances 2. Diameters 3. Masses 4. Densities summary summary Solar System Overview Recall column 1. Distances from the Sun: – – Radar Kepler’s Third Law (empirical) Orbits of planets are nearly circular use Newton’s Laws for a circular orbit of radius “r”. M is mass of sun. Recall: Rearrange: Need velocity to get radius. Solar System Overview: Distances Recall column • 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: summary Solar System Overview: Distances Recall column • Substitute v squared into the equation for radius: Just need to observe the Period to get the distance! summary summary Solar System Overview: We have the distance! Recall column • Kepler’s Third Law -- for ellipses Observe the Period! Using a in au and P in Earth years. a == semi-major axis Orbit of planet sun a Solar System Overview Recall column • Keplerian Rotation Curve. summary summary Solar System Overview Recall column 2. Diameters - from lecture 4 Linear diameter angular diameter --------------------- = ----------------------2 pi * Distance 360 degrees 2 pi * Distance linear diameter = --------------------- * angular diameter 360 degrees We can get the distance between a planet and Earth by using step 1 to get its distance to the sun and then 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. Also for radius of orbits. summary Solar System Overview Recall column 3. Masses Rearrange: use step 2 procedure. 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). Solar System Overview Recall column summary 4. Density And for a sphere: So (Where R is radius.) Mass from step 3. diameter from step 2. Solar System Overview: That is how Recall column do we know some of these values summary Solar System Overview: What does the class already know about the classical planets? Recall column Mass and Radius only relative to Earth. Temperature only in Kelvin. summary • 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? Mercury Recall column summary Messenger: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington Venus: Recall column summary Venus Express/European Space Agency Ultraviolet Image Earth Recall column summary Mars Recall column summary Mars Express/European Space Agency Hebes Chasma Jupiter Recall column New Horizons/NASA IR image. summary summary Saturn Cassini/NASA Recall column summary Uranus Recall column Voyager2/NASA “True” Colour False Colour Neptune Recall column summary Voyager2/NASA Question: Recall column summary • Which is the hottest planet in the solar system? a) Mercury because it is closest to the sun. b) Venus because its clouds cause a runaway greenhouse effect. c) Jupiter because it is like a ministar.