Ch. 28.4 Asteroids, Comets, & MeteoroidsMRS. MARQUES

Terms to Know… Asteroid Comet Kuiper Belt Oort cloud Meteor meteoroid

Asteroids: large rock fragments that orbit the sun in elliptical orbits.Largest known asteroid is Ceres (1,000 km diam.)…also considered a dwarf planet b/c its gravity has caused it to be round.

Asteroid belt is located b/t Mars and Jupiter and contains most asteroids.

Three types based on composition Carbon (these asteroids are dark) Silicate (like Earth rocks) Fe, Ni (rare, shiny-metallic surface)

Near-Earth Asteroids: very small percentage…asteroid detection programs monitor their movements.

Comets: ice, rock, dust, have tails—highly elliptical orbits around sun.

Halley’s Comet-passes Earth every 76 yrs (next = 2061).

Also famous: Hale-Bopp (shown below, 1997), McNaught (2007)

Parts of a comet:

Head

Core (aka nucleus): rock, metals, ice Coma: cloud of gas/dust

2 Tails

Ion tail: Solar wind pushes gas away from the comet’s head so it oalways points away from the sun no matter which direction the

comet is going.

oDust tail: curves behind the comet

Where do comets come from? Some from Kuiper Belt (ring of

icy bodies, including some dwarf planets, beyond Neptune’s orbit)

Most from Oort Cloud (spherical cloud of dust/ice) Could reach as far back as halfway to a near star.

Some comets can have orbits up to a few million years! Those >200 years are called long-period comets.

• Short period comet: <200 years to orbit sun

• Long period comet: > 200 years to orbit sun

Meteoroids: small bits of rock/metal Small meteoroids: detached comet pieces Large meteoroids: result of colliding asteroids.

Meteors: shooting stars or fireballs (bright b/c friction of entering our atmosphere)

Meteor shower: occur at the same time each year with the orbits of comets (comet leftovers).

Meteorites: meteor leftovers that made it to Earth’s surface

• Stony (most are stony)…carbon based• Iron…(easier to find b/c metallic)• Stony-iron (rarest)