Astronomy Notes – Unit 2e – Asteroids,
Comets and Meteoroids
(or the Junkyards of the Solar System)
q (1)
Asteroids (from Greek asteroeides, or starlike)
o Largest
Asteroid Belt Objects are:
§ 1 Ceres – 623 mi (1,003 km) in diameter, first discovered in 1801
·
“promoted” in 2006 to a Dwarf Planet
§
2 Pallas – 300 mi (480 km), discovered in
1802
§
4 Vesta – 240 mi (385 km), discovered in
1807
§
Names have the number in order of discovery, and
a name selected by its discoverer
o Most
are in the Asteroid Belt, between the orbits of Mars
and Jupiter
o More
than 4,000 asteroids have been identified, and scientists believe there may be more
than 10,000 of them larger than 100 km (62 mi) in diameter.
o Shape
is roughly spherical, and smaller ones are long or lumpy
o Composed
of rock, metal,
or both rock and metal
o Trojan Asteroids are grouped together in the
orbital path of Jupiter, with one group ahead of Jupiter and one behind.
q (2) Comets (from Latin stella cometa, or hairy star
)
o A
dirty
snowball with a long,
bright tail.
o Elliptical
orbit passes near the Sun, but mostly spent beyond the orbit of
§
Kuiper Belt –contains the short-period
comets (less than 200 years)
§
Oort Cloud
– contains the long-period comets (more than 200 years)
o Composed
of three parts:
§
Nucleus
– solid part composed of ice and dust
·
6-24 mi (10-40 km) in diameter
§
Coma
– the Sun melts the nucleus to create a cloud of glowing gases
·
As long as 50,000 mi (80,000 km)
§
Tail
– the coma dissipates into two tails
·
Gas tail – blown off by the solar wind,
away from the Sun
·
Dust tail – dust trailing behind the
comet’s orbital path
·
As long as 600,000 mi (1 million km)
o Famous
Comets:
§
Halley’s Comet –appears every 76 years,
first recorded in 466 BC
§
Hale-Bopp – appeared in 1995-97,
brightest in almost a century
§
Shoemaker-Levy – spectacular crash into
Jupiter in 1996
q (3) Meteors
o Meteoroids are small rocky
bodies in space
o Meteors are meteoroids which
enter the Earth’s atmosphere and begins to “burn up” due to the extreme
friction with the air
§
also know as shooting stars
o Meteor Showers happen at certain
times of the year when meteors fall in greater numbers than usual, and seem to
come from specific parts of the sky.
§
names come from constellation from which they
seem to appear
§
See Table in “Astronomy and Space” , page 86
o Meteorites are meteors which do
not entirely burn up in the atmosphere, and impact the Earth’s surface,
creating a crater
o Composed of iron or stone, or both