Announcements. Distances in the Solar System. The Main Point. Lecture #10: Solar System Survey II

Transcription

1 Lecture #10: Solar System Survey II Distances and a Solar System Scale Model Overview of Planetary Atmospheres Terrestrial Planet Atmospheres Jupiter, Saturn, Uranus, Neptune Overview of Solar System Formation Announcements Review sessions: Sunday and Monday 7:30 pm Baker 135 No office hours on Monday Astro 102/104 1 Astro 102/104 2 The Main Point All of the planets with atmospheres in our solar system have distinctive weather and climate. Distances in the Solar System The basic unit: Astronomical Unit (AU): Defined as Earth's average distance from the Sun. 1 AU 150,000,000 km 93,000,000 miles. Can also think of distances in light travel time: Light travels at 300,000 km/sec. 1 AU = 150,000,000 km / (300,000 km/sec) = 500 sec. Earth is a little over 8 light minutes from the Sun. Neptune is more than 4 light hours from the Sun! Nearest star (α Centauri) is 4.3 light years away! Nearby galaxy (Andromeda) is 2.5 million light years away! Astro 102/104 3 Astro 102/

2 A Scale Model! Sagan Planet Walk, downtown Ithaca Terrestrial Planet Atmospheres Venus, Earth, & Mars have substantial atmospheres: How are they similar and different? What can the differences tell us about the different histories of these worlds? Astro 102/104 5 T s=740 K K Ps=90,000 mbar 1000 mbar 10 mbar Astro 102/104 7 Atmospheric Compositions Venus, Earth, and Mars Atmospheric Compositions (in %) Gas Venus Earth Mars CO N Ar O Ne There are substantial differences, with important implications for the weather and climates of these worlds! Astro 102/104 8 Certain gases trap infrared heat and allow planetary surfaces to warm up beyond their "equilibrium" temperatures. Implications: Liquid water, LIFE! Greenhouse Effect (much more detail in Lecture 18) Greenhouse effect on: Mars: Little; Earth: Moderate; Venus: Wild! Astro 102/

3 Inner vs. Outer Planets Fundamental differences! Example: Jupiter vs. Earth Jupiter's radius is 11 times the Earth's. Jupiter's mass is 318 times the Earth's. Jupiter's density is 0.25 times the Earth's. Jupiter is not "rocky" like the Earth: It has no solid surface (can't "stand on Jupiter"). It is made mostly of H 2 and He, just like the Sun. It has a strong source of internal heat. Astro 102/ The Jovian Planets Jupiter Saturn Uranus Neptune D = 5.2 AU D = 9.5 D = 19 D = 30 ρ = 1.3 g/cm 3 ρ = 0.7 ρ = 1.2 ρ = 1.6 T = 125 K T = 95 T = 60 T = 60 P = 12 years P = 30 P = 84 P = 165 Astro 102/ Inside a Jovian Planet How do we know this?? Clouds and Atmospheric Structure Differentiation also appears to have occurred in the giant planets, producing an onion-skin style of layering inside the planets (from lighter gases, to heavier gases, to ice, to rock). Astro 102/ Astro 102/

4 When we see clouds on the giant planets, we are watching their weather and climate. How did it all come together? There are several models of how the solar system formed. How do we decide which is right? (we weren't there!) Do the models rely on the laws of physics and chemistry or do they require miracles or ad hoc assumptions? Do the models accurately predict the present nature and distribution of the planets? Are there clues in the compositions of the planets or comets or meteorites that could help us choose among the models? Can we look elsewhere in the galaxy for evidence of the process of solar system formation? Astro 102/ Astro 102/ Orion Observational Evidence: Nebulae Star-forming Regions The "Standard Model": From gas clouds to gas giants... Astro 102/ Dust disks around nearby stars! Planets around other stars! Astro 102/

5 Summary The terrestrial planets have interesting and diverse atmospheres, weather, and climates. The Jovian planets are almost entirely gaseous, and have compositions like that of the Sun. The "surfaces" " of the Jovian planets are really the tops of deep layers of clouds (NH 4, H 2 O, CH 4,...) Theoretical models and observational evidence indicate that the solar system formed ~4.6 billion years ago from the collapse of an interstellar dust cloud. All these topics will be covered in much more detail in Parts 2, 3, and 4 of the course! Astro 102/ Wed Feb 13 In-class exam #1. Don t panic! Multiple choice exam written by your friendly TAs. Bring #2 pencils. Closed book, independent d work. Have you read and signed the ground rules? No electronic equipment allowed. Formula sheet & fundamental constants will be provided. Memorize the Earth s diameter and Earth-Sun distance! Astro 102/