Transcript Day-39

Astronomy 1010-H
Planetary Astronomy
Fall_2015
Day-39
TNO_Wide-1
Course Announcements
•
SW-chapter 11, 12 due: Wed. Dec. 9
•
Final Exam & Exam -4: 0800-1000 - Wed. Dec. 9
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1st 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 2014.
 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 highaltitude 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.
B.
C.
D.
dust tail
ion tail
nucleus
coma
Concept Quiz
Short-Period Comets
Short-period comets are associated with
what class of
objects?
A.
B.
C.
D.
Kuiper Belt objects
terrestrial planets
the Oort Cloud
the giant planets
PROCESS OF SCIENCE
 Scientific decision-making must follow the
evidence, not affection or popular sentiment.
MATH TOOLS 12.1
 We can relate the eccentricity of an orbit to
the object’s closest approach (perihelion)
and farthest approach (aphelion).
CONNECTIONS 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.
MATH TOOLS 12.2
 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 1014 kg
and a speed of 20 km/s have?