Astronomy 1010-H Planetary Astronomy Fall_2015 Day-39

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Course Announcements SW-chapter 11, 12 due: Wed. Dec. 9 Final Exam & Exam -4: Wed. Dec. 9 1 st Thursday Art Walk – 5-8pm on Study Day

 Comet nucleus is an ice/rock mix.  “Dirty snowballs.”  Size of nucleus ranges from a few dozen meters to a several hundred kilometers.  This is the comet’s appearance when far from the Sun.

 When near the Sun: active comets.  Sun heats the icy nucleus, causing sublimation.  Sublimation forms: Coma. Ion tail. Dust tail.

 Comets have two tails.  Ion tail created by the solar wind interacting with ions of the nucleus.  Dust tail created from solar wind and sunlight.  Comet tails point away from the Sun.

 Seven comets have been visited so far by spacecraft, with one more in  A projectile hit Comet Tempel 1 in order to study its contents.

 Large collisions in space are not frequent, but they occur.  1994: Comet Shoemaker-Levy 9 crashed into Jupiter, leaving visible scars.

 Comet or asteroid impacts on Earth are infrequent, but devastating.  1908: Tunguska event was possibly the high- altitude explosion of an asteroid or comet.

 Meteorites are pieces of asteroids that have fallen to Earth.  In space, a meteorite is called a meteoroid.  While passing through the atmosphere, it is a meteor.

 Comet nucleus disintegration and asteroid collisions make debris.  Earth passing through a collection of debris results in meteor showers, such as the Perseids or Leonids.  Single pieces of debris result in sporadic meteors.

 Meteorites are pieces of asteroids.  Over 90% are stony, like Earth rocks.  Chondrites have chondrules; achondrites do not; some have carbon.  Can use meteorites to date the age of the Solar System (4.5 billion years).

 Iron meteorites have high concentrations of metal, with a melted and pitted appearance.  Stony-iron meteorites are a combination and are relatively rare.

 Sunlight reflects off ground-up asteroid and cometary debris in the inner Solar System.  This zodiacal dust in the plane of the Solar System makes the zodiacal light.

 Comets and asteroids have affected life on Earth in the past and may in the future.  In the early history of Earth, icy planetesimals most likely collided with Earth and deposited water.  Comets also possess complex organic material.  Life on Earth is threatened in the future by potential comet and asteroid collisions.

Concept Quiz—Asteroids Asteroids are made of A.dust and gas. B.ices and dust. C.rock and metal. D.frozen carbon dioxide (“dry” ice).

Concept Quiz—Distant Comets A distant comet at its farthest point from the Sun would have which of the following? A. dust tail B. ion tail C. nucleus D. coma

Concept Quiz Short-Period Comets Short-period comets are associated with what class of objects? A. Kuiper Belt objects B. terrestrial planets C. the Oort Cloud D. the giant planets

 Scientific decision-making must follow the evidence, not affection or popular sentiment. PROCESS OF SCIENCE

 We can relate the eccentricity of an orbit to the object’s closest approach (perihelion) and farthest approach (aphelion). MATH TOOLS 12.1

 There are areas in the asteroid belt that lack asteroids (Kirkwood gaps).  These correspond to orbital resonances with Jupiter.  Repeated tugs from Jupiter would prevent an asteroid from staying in that orbit. CONNECTIONS 12.1

 The energy that can be released by the impact of a comet nucleus is equal to its kinetic energy:  How much energy does a 10-km diameter comet nucleus with a mass of 5 x kg and a speed of 20 km/s have? MATH TOOLS 12.2