LECTURE 13, OCTOBER 7, 2010 ASTR 101, SECTION 3 INSTRUCTOR, JACK BRANDT 1ASTR 101-3, FALL 2010

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HALLEY’S COMET First comet to have its return predicted. Occurred in 1759 AD, a triumph of celestial mechanics Seen at nearly every apparition since 239 BC Returns on average every 76 years Last return was in 1986 AD & 5 spacecraft were sent to its vicinity Next return is in 2061 AD 5

ASTR 101-3, FALL 20106

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ASTR 101-3, FALL 2010 PROCESSES IN COMETS-1 The basic process is sublimation, the direct transition from solid water ice to vapor Produces water vapor and releases dust particles and other gases trapped in the ice All cometary phenomena ultimately originate with material in the nucleus Energy source is solar radiation as the nucleus approaches the sun 11

ASTR 101-3, FALL 2010 PROCESSES IN COMETS-2 Gas and dust emission comes from localized areas on the surface of the nucleus After sublimation occurs from the surface layers, a loose, dust crust remains. Confirmed by Deep Impact Dust and gas (atoms & molecules) flow outward to form the coma and hydrogen cloud 12

ASTR 101-3, FALL 2010 PROCESSES IN COMETS-3 Solar radiation pressure pushes dust particles anti-sunward to make the dust tail Some molecules are ionized (electrically charged) and are carried anti-sunward by the solar wind to form the ion/plasma tail 13

TEXT PROBLEM, PAGE 111, ETC. The text statement: “Both types of tails are in all cases directed away from the Sun by the solar wind, an invisible steam of matter and radiation of escaping from the Sun.” This is wrong. See previous slide. Also, the solar wind is composed of particles and magnetic fields, but not radiation. ASTR 101-3, FALL

ASTR 101-3, FALL

ASTR 101-3, FALL

Question 9 Compared to asteroids, comets show all of these properties EXCEPT a)their densities are higher. b)their orbits tend to be more elliptical. c)they tend to be made of ice. d)they can look fuzzy, whereas asteroids appear as moving points of light. e)their average distances from the Sun are far greater. 17ASTR 101-3, FALL 2010

Question 9 Compared to asteroids, comets show all of these properties EXCEPT Comets have densities much lower than asteroids or planets. a)their densities are higher. b)their orbits tend to be more elliptical. c)they tend to be made of ice. d)they can look fuzzy, whereas asteroids appear as moving points of light. e)their average distances from the Sun are far greater. 18ASTR 101-3, FALL 2010

DISCONNECTION EVENTS Occasionally, the entire ion/plasma tail disconnects from the head region A new ion/plasma tail is formed Produced by a specific feature in the solar wind 19

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ASTR 101-3, FALL

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What causes a meteor shower? Question 10 a) A comet and an asteroid collide. b) Earth runs into a stray swarm of asteroids. c) Earth runs into the debris of an old comet littering its orbit. d) Meteorites are ejected from the Moon. e) Debris from a supernova enters Earth’s atmosphere 26ASTR 101-3, FALL 2010

What causes a meteor shower? Question 10 Meteor showers can generate a few shooting stars, to hundreds of thousands, seen in an hour. a) A comet and an asteroid collide. b) Earth runs into a stray swarm of asteroids. c) Earth runs into the debris of an old comet littering its orbit. d) Meteorites are ejected from the Moon. e) Debris from a supernova enters Earth’s atmosphere 27ASTR 101-3, FALL 2010

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ASTR 101-3, FALL

ASTR 101-3, FALL

Question 12 a) a cold terrestrial planet. b) a small jovian planet. c) a large Kuiper belt object. d) a wandering moon. e) a captured comet. Many astronomers believe Pluto is perhaps best classified as 31ASTR 101-3, FALL 2010

Many astronomers believe Pluto is perhaps best classified as Question 12 a) a cold terrestrial planet. b) a small jovian planet. c) a large Kuiper belt object. d) a wandering moon. e) a captured comet. Several other large Kuiper belt objects have been discovered, including the largest known, called Eris. 32ASTR 101-3, FALL 2010

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