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Lec17-Mar24

# Lec17-Mar24 - Key Concepts •  Density and...

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Unformatted text preview: 3/24/10 Key Concepts •  Density and composiCon Astro 109 Lecture 17: Our Solar System •  Terrestrial vs. Jovian planets •  Moons March 24 •  Asteroids, comets, Kuiper belt objects Mar. 24 ★ Note: relaCve sizes are accurate; spacings are not to scale. Mar. 24 Mar. 24 How can we tell what they are made of? Discussion QuesCon •  Solid / liquid / gas ? What informaCon can we use to determine the mass of Mars? •  Rock / water / air – How might we characterize the diﬀerence between them? A.  B.  C.  D.  E.  density = mass volume kg/m3 2000—3000 2—3 water Mar. 24 g/cm3 rock 1000 1 air 1.3 0.0013 The orbit of Mars around the Sun (orbital size and period). The orbits of Mars’s moons (orbital sizes and periods). Mars’s rotaCon period. The color of Mars’s surface. The number of craters on Mars’s surface. Mar. 24 1 3/24/10 Example: Mass of Mars Mars has two small satellites, Phobos and Deimos. Phobos circles Mars once every 0.31891 day at an average alCtude of 5980 km above the planet’s surface. The diameter of Mars is 6794 km. R = 3397 km Example: Density of Mars a = 3397 km + 5980 km = 9377 km P = 0.31891 d × = 27554 s 2 [P (s)] M 86400 s 1d Mars has two small satellites, Phobos and Deimos. Phobos circles Mars once every 0.31891 day at an average alCtude of 5980 km above the planet’s surface. The diameter of Mars is 6794 km. R [a (km)]3 M (M⊕ ) 93773 = 10−4 × × M⊕ 275542 5.974 × 1024 kg = 0.11 M⊕ × M⊕ = 6.5 × 1023 kg = 10−4 × Mar. 24 = 3397 km 4 π R3 3 ￿3 4￿ = π 3.397 × 106 m 3 = 1.64 × 1020 m3 volume = density 6.5 × 1023 kg 1.64 × 1020 m3 = 3, 900 kg m−3 = Mar. 24 Example: Density of Earth Discussion QuesCon Mass = 5.97×1024 kg, diameter = 12,576 km, radius = 6,378 km The average density of Earth is higher than that of typical rock. What does this suggest? 4 π R3 3 ￿3 4￿ = π 6.378 × 106 m 3 = 1.09 × 1021 m3 volume = density 5.97 × 1024 kg 1.09 × 1021 m3 = 5, 500 kg m−3 = Mar. 24 A.  Gravity from the Moon increases Earth’s density. B.  Earth’s rotaCon increases its density. C.  There must be a signiﬁcant amount of ice under high pressure inside our planet. D.  There must be a signiﬁcant amount of material denser than rock inside our planet. E.  Dirt is denser than you thought. Mar. 24 Discussion QuesCon DensiCes of the Planets Planet 5430 Venus 5243 Earth 5515 Mars 687 Uranus 1318 Neptune Planet Density (kg/m3) A. Earth 5515 B. Jupiter 1326 C. Saturn 687 D. Uranus 1318 E. 1326 Saturn Rocky, with dense iron cores 3934 Jupiter Mar. 24 Which planet would ﬂoat in water? Density (kg/m3) Mercury Neptune 1638 1638 Mostly light elements (hydrogen, helium) Mar. 24 2 3/24/10 ★ Jupiter’s Galilean Satellites Mar. 24 Mar. 24 Saturn’s Moon Titan http://saturn.jpl.nasa.gov/science/moons/" Mar. 24 Mar. 24 Discussion QuesCon Which of the following is not a characterisCc that disCnguishes Jovian from terrestrial planets? A.  B.  C.  D.  E.  Mar. 24 size number of moons mass composiCon orbital eccentricity Mar. 24 3 3/24/10 Main asteroid belt Asteroids Mar. 24 Mar. 24 Comets Mar. 24 Kuiper Belt Mar. 24 Discussion QuesCon What properCes of Pluto led to its reclassiﬁcaCon as a trans ­ Neptunian object or Kuiper Belt object? A.  It has a highly eccentric, inclined orbit. B.  It is a rocky object in the outer solar system. C.  It is signiﬁcantly smaller than any other planet in the solar system. D.  Many other trans ­Neptunian objects the size of Pluto have been discovered. E.  All of the above. Mar. 24 Mar. 24 4 3/24/10 Learning from diversity •  Why are the inner planets small and rocky, while the outer planets are big and gaseous? •  Why do some objects have atmospheres while others don’t? •  What are rings? •  Why are some objects cratered while others are smooth? •  What are the asteroids, comets, and Kuiper belt objects? Mar. 24 Mar. 24 Stay tuned! HW quesCons 2.  What are the characterisCcs of a terrestrial planet? 3. What are the characterisCcs of a Jovian planet? 4. What is meant by the average density of a planet? What does the average density tell us? 7. What are the diﬀerences in chemical composiCon between the terrestrial and Jovian planets? 22. Mars has two small satellites, Phobos and Deimos. Phobos circles Mars once every 0.31891 day at an average alCtude of 5980 km above the planet’s surface. The diameter of Mars is 6794 km. Using this informaCon, calculate the mass and average density of Mars. Mar. 24 5 ...
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