Exam #2 Study Guide. March 10, 2016

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1 Exam #2 Study Guide March 10, 2016

2 Solar System Constituents The terrestrial planets are made primarily of rock and metal. The Jovian planets are made primarily of hydrogen and helium; also have large amounts of water, methane, and ammonia Moons (a.k.a. satellites) orbit the planets; some moons are large.

3 The terrestrial planets are made primarily of rock and metal. Mercury, Venus, Earth, & Mars. The terrestrial planets are: low in mass (< Earth mass) high in density (> 3900 kg/m 3 ). Water = 1000 kg/m 3 Air = 1 kg/m 3 Rock = 3000 kg/m 3

4 The Earth The study of seismic waves tells us about the Earth s interior. The Earth is layered into crust, mantle, inner core, and outer core. The Earth is layered because it underwent differentiation when molten. The crust is broken into plates that move relative to each other.

5 The Moon The Moon s surface has both smooth maria and cratered highlands. The surface was shaped by heavy bombardment, followed by lava floods. The Moon has a thick crust but a tiny iron-rich core. The Moon may have been ejected when a protoplanet struck the Earth.

6 Mercury Mercury has a 3-to-2 spin-orbit coupling (not synchronous rotation). Mercury has no permanent atmosphere because it is too hot. Like the Moon, Mercury has cratered highlands and smooth plains. Mercury has an extremely large iron-rich core.

7 Venus The surface of Venus is hidden from us by clouds of sulfuric acid. The atmosphere of Venus is hot because of a runaway greenhouse effect. The surface of Venus shows volcanic activity but no plate tectonics. The interior of Venus is similar to that of the Earth.

8 Mars Mars has a tenuous atmosphere, with little water vapour and few clouds. Mars has large volcanoes and a huge rift valley, but no plate tectonics. Robotic rovers have given us a close-up look at Mars. Mars has two small irregular moons, Phobos and Deimos.

9 Jupiter and Saturn Jupiter and Saturn consist mainly of hydrogen and helium. Jupiter and Saturn have belts and zones of clouds, plus circular storms. Jupiter and Saturn have magnetic fields created in metallic hydrogen. Differences between Jupiter and Saturn are due to Jupiter s higher mass. All Jovian planets have rings.

10 Moons of Jupiter and Saturn The Galilean Moons of Jupiter: Callisto: heavily cratered Ganymede: larger then Mercury Europa: covered with smooth ice Io: volcanically hyperactive The Giant Moon of Saturn: Titan: wrapped in an atmosphere

11 Uranus and Neptune Uranus and Neptune are nearly identical in their internal structure. The rotation axis of Uranus is tilted by about 90 degrees, causing extreme seasons. Neptune has surprisingly strong storms, driven by internal heat. Triton, the giant moon of Neptune, is a cold world with nitrogen geysers.

12 Pluto... and Beyond Pluto and its moon Charon are icy worlds that resemble Triton. The Kuiper belt, beyond Neptune, contains small, icy, Pluto-like objects. Some are more massive than Pluto! The icy Kuiper Belt Objects are leftover planetesimals. Comets are dirty snowballs : ice mixed with dust & carbon compounds. Most comets are in the Kuiper belt or the Oort cloud, far from the Sun. A comet or asteroid impact may have caused the extinction of dinosaurs Studies of the Outer Solar System continue.

13 Origin of the Solar System How the Solar System formed: A cloud of gas & dust contracted to form a diskshaped solar nebula. The solar nebula condensed to form small planetesimals. The planetesimals collided to form larger planets. When the Solar System formed: Radioactive age-dating indicates the Solar System is 4.56 billion years old.

14 The contraction of the solar nebula made it spin faster and heat up. (Compressed gas gets hotter.) Temperature of solar nebula: > 2000 Kelvin near Sun; < 50 Kelvin far from Sun.

15 How does this nebular theory explain the current state of the Solar System? Solar System is disk-shaped: It formed from a flat solar nebula. Planets revolve in the same direction: They formed from rotating nebula. Terrestrial planets are rock and metal: They formed in hot inner region. Jovian planets include ice, H, He: They formed in cool outer region.

16 Planets Outside Our Solar System More than 2000 planets known Very difficult to detect Radial velocities and transit depths are small Rapidly changing number First was found in 1995 (radial velocity variation) Many large planets known close to host star Hot Jupiters because they are the mass of Jupiter, but close enough to star to be hot Many multiple planet systems known Challenges to existing nebular theory of planet formation Continues to be an exciting field of astrophysics

17 Distances to Stars Distance is important but hard to measure for objects outside the solar system Trigonometric parallaxes direct geometric method only good for the nearest stars (~500pc) Units of distance in Astronomy: Parsec (Parallax second) or pc Light Year Closest Star is about 1pc away

18 Luminosity and Brightness Luminosity of a star: total energy output independent of distance Apparent brightness of a star: depends on the distance by the inverse-square law of brightness (Apparent Brightness scales like Luminosity/Distance 2 ) measured quantity from photometry.

19 Stellar Colors and Spectra Color of a star depends on its Temperature Red Stars are Cooler Blue Stars are Hotter Spectral Classification Classify stars by their spectral lines A type has strongest H absorption Spectral differences mostly due to Temperature Spectral Sequence (Temperature Sequence) O B A F G K M The Sun is a G star

20 Stellar Masses and Radii Types of binary stars Visual Spectroscopic Eclipsing Only way to measure stellar masses: Only roughly a few hundred stars Some stars are more massive than the Sun (about 100times) Some stars are less massive than the Sun (about 0.1 times) Radii are measured for few stars Very wide range of stellar radii

Chapter 6 Formation of Planetary Systems Our Solar System and Beyond

Chapter 6 Formation of Planetary Systems Our Solar System and Beyond The solar system exhibits clear patterns of composition and motion. Sun Over 99.9% of solar system s mass Made mostly of H/He gas (plasma)