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Asteroids… Comets… Meteoroids
Asteroids
• Fragments of rock that
orbit the sun.
• More than 50,000 total
• Orbit in elliptical paths
• Most located in the
Asteroid Belt
– Between Mars
and Jupiter
– Others are closer to the
sun and others are
beyond Jupiter
• The largest is Ceres,
1,000 km in diameter
– Large enough so that
gravity has made it round;
first classified as an
asteroid, now as a dwarf
planet!
Composition of Asteroids
– Similar to inner planets
 rocky
– Classified/Grouped
according to their
composition
– 3 types of asteroids
1. Carbon – dark
(common)
2. Silicate – like earth
rocks
3. Iron/nickel –
shiny/metallic (rarest)
Near-Earth Asteroids “NEA”
Asteroids whose orbits
bring them close to
earth.
– More than 1,000
– Possible dangers to
earth
– Example:
Meteor crater, Arizona
50 m asteroid
1 km crater
40,000 years ago
• NASA has a congressional
mandate to catalog all
near-Earth objects.
Object
Name
Close
Approach
Date
CA
Distance*
(AU)
CA
Distance*
(LD)
Estimated
Diameter**
H
(mag)
Relative
Velocity
(km/s)
138127 (2000
EE14)
2015-Feb-27
0.1864
72.5
1.0 km - 2.3 km
17.1
20.25
90416 (2003
YK118)
2015-Feb-27
0.0782
30.4
530 m - 1.2 km
18.5
10.22
(2014 TA36)
2015-Feb-27
0.1520
59.1
190 m - 430 m
20.7
12.31
(2015 DP53)
2015-Feb-28
0.0510
19.8
36 m - 80 m
24.4
8.58
(2014 YS34)
2015-Feb-28
0.0978
38.1
180 m - 410 m
20.8
6.94
(2015 DN53)
2015-Mar-01
0.1024
39.8
28 m - 62 m
24.9
7.57
Comets
• Small bodies of ice, rock , and cosmic dust
that follow elliptical orbits around the
sun.
• Example:
– Halley’s comet, 1986, next 2061
• Every 76 years.
– Hale-Bopp, 1997, next 4385
Two parts
• Body:
– Core or nucleus: made of rock, metal or
ice (dirty snowball).
– Coma: spherical cloud of gas and dust
surrounds core.
• Tail:
– Longer Tail = gas lit up by solar wind
– Shorter Tail = dust reflecting visible
sunlight
• Comets reflect light
from the sun
(off coma and tail)
• The solar wind
blows the tail of the
comets.
• Therefore, the tail of
a comet always
points away from the
streaming particles of
the solar wind, or
away from the sun.
• Long period comets
take more than 200 years
to orbit.
• Short period comets
take less than 200 years
to orbit the sun.
Oort Cloud
• Where most comets originate (come from)
• A spherical cloud of dust and ice
• Lies beyond Neptune’s orbit and the Kuiper
belt, surrounds our solar system.
• Contains billions of nuclei of comets
• All in elliptical orbits around the sun; very slow
orbits; it may take some of them a few million
years to complete one orbit!
Meteoroids
Meteors
• The smaller rocky, icy,
or metallic bodies that
move throughout the
solar system.
• Meteoroids that enter
Earth’s atmosphere.
– They compress the
surrounding air quickly,
heating it up intensely
– Most burn up in the
Earth’s mesosphere
– Meteors are the bright
streak of light caused by
this.
– Also called shooting stars
– Many create a meteor
shower
When to look for meteor showers
• Perseids…mid August….50-75/hr (perseids of 2015 below)
• Leonids … Peak Nov. 12-13…15/hr
• Geminids… peak Dec. 13-14
Meteorites
• Millions of meteoroids enter Earth’s atmosphere each day
(they can be very small).
• Some do not burn up… very large to begin with
• A meteoroid or any part of a meteoroid that hits the
earth is a meteorite.
• Most easily found in the Antarctic.
• 3 types
– Stony (like rocks on Earth)
– Iron (metallic looking)
– Stony-iron (rare)