Lec17-Mar22 - 3/22/11 Quiz Ques6on #1 Which of the...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 3/22/11 Quiz Ques6on #1 Which of the following is not an observed paFern in our solar system? Astro 109 Lecture 17: Forma6on of the Solar System March 22 A.  B.  C.  D.  All planets orbit the Sun in the same direc6on. The orbits of the major planets lie nearly in a plane. Most planets orbit the Sun at the same speed. Most planets rotate in the same direc6on as their orbital mo6on. E.  Most moons orbit their planets in the same direc6on as the planets’ rota6on. Mar. 22 Quiz Ques6on #2 In order to be successful, a theory of planet forma6on must explain A.  B.  C.  D.  E.  the orderly mo6ons of the planets. why planets fall into two major categories. why asteroids and comets reside where they do. any excep6ons to the general rules. all of the above. Mar. 22 Key Concepts •  Radiometric da6ng, age of Solar System •  Condensa6on model for planet forma6on •  Atmospheric evapora6on –  gas temperature and mo6on –  escape velocity Mar. 22 Features of the Solar System How old is the Solar System? •  Earth is geologically ac6ve  ­ ­> few features are truly old size and composi6on orderly mo6on Mar. 22 Mar. 22 1 3/22/11 Radiometric da6ng How old is the Solar System? Parent element Daughter element Half ­life (years) Rubidium (87Rb) Stron6um (87Sr) 47.0 billion Uranium (238U) Lead (206Pb) 4.5 billion Potassium (40K) Argon (40Ar) 1.3 billion Carbon (14C) •  But meteorites can be much older Nitrogen (14N) 5730 http://www.solarviews.com/eng/meteor.htm" Solar System is about 4.5 billion years old Mar. 22 Mar. 22 Discussion Ques6on Discussion Ques6on Three ­quarters of the radioac6ve potassium (40K) originally contained in a certain volcanic rock has decayed into argon (40Ar). How long ago did this rock form? In radioac6ve decay, how much of the original element is lef afer one half ­life has elapsed? A.  B.  C.  D.  E.  Mar. 22 Mar. 22 Discussion Ques6on Discussion Ques6on In radioac6ve decay, how much of the original element is lef afer two half ­lives have elapsed? A.  B.  C.  D.  E.  100% 75% 50% 25% none 100% 75% 50% 25% none Radioac:ve decay Three ­quarters of the radioac6ve potassium (40K) originally contained in a certain volcanic rock has decayed into argon (40Ar). How long ago did this rock form? A.  B.  C.  D.  E.  120.00% 100.00% 80.00% 60.00% 40.00% 20.00% 1.3 billion years 2 billion years 2.6 billion years 4.5 billion years 9 billion years Parent element Daughter element Half ­life (years) Rubidium (87Rb) Stron6um (87Sr) 47.0 billion Uranium (238U) Lead (206Pb) 4.5 billion Potassium (40K) Argon (40Ar) 1.3 billion Carbon (14C) Nitrogen (14N) 5730 0.00% 0 Mar. 22 2 4 6 8 10 Mar. 22 2 3/22/11 E=mc2 Raw materials Nuclear crisis in Japan •  Nuclear power: energy from radioac6ve decay  ­ ­> heat water Parent (Main) Daughter Half ­life Uranium ­235 Thorium ­231 700 million years •  Health concern: some byproducts are themselves radioac6ve; if ingested, they can kill cells and/or cause muta6ons (cancer) •  Par6cular concern: isotopes that are easily absorbed in the human body Parent Mar. 22 Daughter Half ­life Iodine ­131 Xenon ­131 8.0 days Cesium ­137 Barium ­137 30.2 years Mar. 22 Why why why? Cosmic abundances large, gaseous, diffuse created in the Big Bang forged in stars Mar. 22 small, rocky, dense Theory: •  Solar system formed from a spinning cloud of gas and dust. •  Planetesimals formed when par6cles stuck together. •  Planets grew by collec6ng more planetesimals and par6cles. Mar. 22 Condensa6on – water Solar Nebula Warm Colder gas (vapor) Mar. 22 Cooler liquid solid Mar. 22 3 3/22/11 Discussion Ques6on How do the condensa6on temperatures of water and rock compare? A.  Water has a higher condensa6on temperature than rock. B.  Rock has a higher condensa6on temperature than water. C.  Water and rock have the same condensa6on temperature. Mar. 22 Mar. 22 Condensa6on model Discussion Ques6on Judging from planetary composi6ons, where was the frost line in the solar nebula? A.  B.  C.  D.  E.  between the orbits of Venus and Earth outside Pluto’s orbit between the orbits of Saturn and Uranus inside Mercury’s orbit between the orbits of Mars and Jupiter Mar. 22 Mar. 22 Atmospheric evapora6on Par6cles in a gas •  Why do some planets/moons have atmospheres while others don’t? •  A gas contains a myriad of atoms/ molecules flying around. •  Is it just forma&on, or also evolu&on? •  Consider par6cle mass m and temperature T: •  How long can a planet/moon retain an atmosphere? typical speed: vgas = ￿ 3kT m k = 1.38 × 10−23 kg m2 s−2 K−1 Mar. 22 Mar. 22 4 3/22/11 Example Discussion Ques6on Earth’s atmosphere contains a lot of molecular nitrogen, N2, which has a par6cle mass of 4.7×10 ­26 kg. Room temperature is about 300 K. How fast are the nitrogen molecules moving? We just calculated the typical speed of nitrogen (N2) molecules in Earth’s atmosphere. What about hydrogen (H2, less massive) and oxygen (O2, more massive) molecules? vgas = = ￿ ￿ 3kT m 3 × (1.38 × 10−23 kg m2 s−2 K−1 ) × (300 K) 4.7 × 10−26 kg = 515 m/s A.  B.  C.  D.  E.  H2 molecules move faster and O2 molecules move slower H2 molecules move slower and O2 molecules move faster both H2 and O2 molecules move slower both H2 and O2 molecules move faster all molecules move at the same speed. vgas = Mar. 22 ￿ 3kT m Mar. 22 Example Escape velocity •  If you throw something fast, you can throw it into orbit. Earth’s mass is 5.97×1024 kg and its radius is 6.38×106 m. What is its escape velocity? •  If you throw it fast enough, you can throw it out of orbit! vesc ￿ 2GM R 2 × (6.67 × 10−11 m3 kg−1 s−2 ) × (5.97 × 1024 kg) = 6.38 × 106 m = 1.12 × 104 m/s = 11.2 km/s = ￿ •  To escape from planet with mass M and radius R: ￿ 2GM vesc = R Mar. 22 Mar. 22 Atmospheric evapora6on •  Roughly speaking, a planet can retain its atmosphere only if vgas < vesc /6 T (K) vesc vesc/6 Mercury 452 4.2 0.7 vgas (H2) vgas (He) 2.4 1.7 Venus 726 10.4 1.7 3.0 2.1 Earth 281 11.2 1.9 1.9 1.3 Mars 150 5.0 0.8 1.4 1.0 Jupiter 120 59.5 9.9 1.2 0.9 Saturn 88 35.5 5.9 1.0 0.7 Mar. 22 5 ...
View Full Document

This note was uploaded on 01/19/2012 for the course ASTRO 109750 taught by Professor Keeting during the Fall '11 term at Rutgers.

Ask a homework question - tutors are online