Chapter 12- Meteoroids and Comets

Question 1

Meteor

Answer 1

Streaks of light in the sky caused when meteoroids partially or totally burn up in the atmosphere. There are usually more meteors visible after midnight because then Earth’s atmosphere is rotating into the same direction as its orbital motion: it is more likely to overtake any meteoroids in its path.

Question 2

Meteoroids

Answer 2

Small pieces of rock and debris orbiting the Sun. Size range is usually defined as between 100 m and 100 m. Larger objects are planetesimals, smaller are dust.

Question 3

Meteorite

Answer 3

Meteorites are the rock fragments which survive their fall to Earth.

Question 4

Types of Meteorites

Answer 4

Most common are Stony meteorites (about 95%) which are silicate rocks (silicon+oxygen+other stuff) like many of the rocks on Earth’s surface, These are the vast majority of falls, but they are hardest to find because the resemble ordinary rock.

Remaining (about 5%) are Irons (mostly iron and nickel) and Stony Irons (a mixture as the name indicates).

Relatively easy to find meteorites in the ice sheet of Antarctica.

Question 5

Chondrites

Answer 5

Some Stony meteorites contain chondrules, glassy spheres which result when silicates are heated and then cooled rapidly. Such meteotites are called chondrites.

A very rare and important type of Stony is the carbonaceous chondrite. These contain carbon compounds, in particular amino acids – the building blocks of proteins which are an important component of living organisms.

Heat would have destroyed these delicate compounds – so these objects have not been heated and have apparently been floating around the solar system since its formation 4.56 billion years ago. Their composition must be a reflection of the early solar nebula.

Question 6

Allende

Answer 6

Large carbonaceous chondrite which fell in Mexico in1969.It contained 26Mg, a stable decay product of radioactive 26Al. We believe 26Al is produced in supernova explosions.

Suggests that a supernova explosion occurred nearby which may have triggered the collapse of the dark dust cloud which formed the solar nebula at the time.

Question 7

Difference between an asteroid and a comet nuclei

Answer 7

Asteroids are mostly of rocky and metallic composition. They lie in the asteroid belt, most between Jupiter and Mars, where they have generally circular orbits near the plane of the ecliptic.

Comet nuclei are a mixture of rocks and ices (“dirty snowball”). Many have highly eccentric orbits outside the plane of the ecliptic.

Question 8

Where do comets come from?

Answer 8

Short period comets( less than 20 years)- inner part of the Kuiper belt. Longer period- Oort Cloud.

Question 9

Comet tails

Answer 9

Ion tail, dust tail.

Ion tail- less massive ions pushed away from the sun

Dust tail- more massive dust marks the gently curving orbit