Phys 1830: Lecture 20 Mars Express/ESA Test This Friday! The “review” is online at the class website. Office Hour Monday - today - 3pm including image review. Messenger/NASA – news announcement Tuesday Previous Class: Solar System in general Solar System Formation This Class Solar System Next Classes: Solar system, Solar System formation, specific planets Exoplanets ALL NOTES COPYRIGHT JAYANNE ENGLISH The state of the affairs from the previous class is that we measure arcs on the sky. The image website is taking shape. Please send your piks and your names.

Solar System Overview: Material for our contest! How do we know these things? The first 8 are planets

Mercury is the hottest planet because it is closest to the sun. Prediction: Mercury is the hottest planet because it is closest to the sun. a) True b) False

Does it rotate and revolve in the same direction as the other planets? Solar System Overview: What does the class already know about the classical planets? For each planet: Does it rotate and 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? Mass and Radius only relative to Earth. Temperature only in Kelvin. If a planet spins in the same direction as its orbit, its spin is called “prograde”. If a planet spins in the opposite direction to its orbital motion, that spin is called “retrograde”. Do your own research to supplement these powerpoint presentations.

Mercury Impact craters Messenger: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington Impact craters Evidence of lava flows (volcanic activity) in smooth parts Surface Temperature 100-700K

Mercury Got back to my desk and some last minute images were there!

Venus

Venus

Venus: Venus Express/European Space Agency Ultraviolet Image White regions are sulfuric acid clouds. Surface Temperature 730K Revolves backwards

Earth Notable that it has a moon, life (possibly intelligent), etc. Mean Surface Temperature 290K (290 – 273 = 17C) 1 moon

Mars Mars Express/European Space Agency Hebes Chasma High Resolution Stereo Camera aboard Mars Express. Four colour filters. Mean Surface Temp 210K … about -50C around the equator. 2 moons

Jupiter New Horizons/NASA IR image. The moon in the image is IO – this is a montage. 3 IR bands  white Red Spot. Temperature at cloud tops: 124K At least 61 moons

Saturn Cassini/NASA 97K at cloud tops At least 31 moons

Uranus “True” Colour False Colour Voyager2/NASA Rolls in its orbit Mean Surface Temperature 58K At least 27 moons

Neptune Voyager2/NASA Blue since methane absorbs red light. Mean surface temperature 59K At least 13 moons.

Pluto, because it is the smallest planet. 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.

Which is the hottest planet in the solar system? Question: Which is the hottest planet in the solar system? Mercury because it is closest to the sun. Venus because its clouds cause a runaway greenhouse effect. Jupiter because it is like a mini-star. Venus is roughly 750K

Solar System Overview: That is how do we know some of these values You could actually calculate these things! Note that a table like this shows us that Jupiter and the outer planets have lower density than the inner planets.

Does it revolve in the same direction as the other planets? Solar System Overview: What does the class already know about the classical planets? 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? Two main types of classical planets. We asked these sorts of questions.

Solar System Overview: Jovians are gaseous but thought to have molten, not solid, cores of terrestrial composition. Terrestrials: Mercury, Venus, Earth, Mars Jovians: Jupiter, Saturn, Uranus, Neptune

Solar System Overview: Interplanetary Debris Comet Holmes (Pierre Tremblay 2007) Asteroids visited by spacecraft up to 2008. NASA This is another feature of the solar system that our theories of planetary system formation need to explain. The category is the predominant material – note that rocky has some ice and icy has some rock. The diameter of the dwarf planet Ceres (which resides in the Asteroid Belt) is roughly 900 km. The asteroids are old. Comets come from KB and Oort cloud. Type Diameter Category Asteroids > 100m rocky Meteroids < 100m rocky Comets 1 – 10 km icy

Review Question A Solar System object categorized as having a rocky composition and that is comparable in size to a small city is most likely: A meteroid A comet An asteroid A planet.

Planetary System Formation A theory needs to explain: Why planets orbit in a plane Why planets orbit in the same direction Why some revolve backwards (Venus) or roll (Uranus) Why inner planets are small and rocky Why outer planets are large and gaseous Why asteroids are old Why Kuiper Belt Objects (KBO) and Oort cloud comets are icy The plane that the planets orbit in is the plane of the ecliptic. Looking from the earth to the sun, as the earth moves in its orbit the sun appears to trace a path along the celestial sphere. The path is called the ecliptic.