Topic 2.2 - Comets & Meteors

Question 1

What are comets?

Answer 1

Cometa are balls of rock and ice that form tails in the course of their highly-elliptical orbits around the Sun

Question 2

What are the comets two types of tail called?

Answer 2

Dust and Ion

Question 3

What is the difference between a dust tail and an ion tail?

Answer 3

An ion tail points in the opposite direction to the Sun whereas a dust tail follows the way the comet is moving

Question 4

When do comets develop tails?

Answer 4

As they approach the Sun

Question 5

What is a short period comet?

Answer 5

They have periods of less than 200 years and originate from the Kuiper belt. They’re 30-50 AU from the Sun

Question 6

What is a long period comet?

Answer 6

They have periods of more than 200 years and can be up to millions. They originate from the Oort Cloud which is brought 50,000 AU from the Sun

Question 7

What do observations of long period comets indicate?

Answer 7

1. Their paths around the sun are in either sense (clockwise or anticlockwise)
2. Orbits are often highly inclined to the ecliptic
3. The high percentage of them originate at vast distances (typically 50,000 AU) from the sun

Question 8

What happens to a comet as it approaches the Sun?

Answer 8

Its temperature rises and gas and dust form an extremely rarefied spherical coma that surround the nucleus, up to 100,000 km across

Question 9

Describe an ion tail.

Answer 9

It’s blue-coloured and straight, consisting of atoms and molecules of gas (most carbon monoxide) that have been ionised by the solar wind; when they de-excite, atoms emit light by fluorescence

Question 10

Describe a dust tail.

Answer 10

It’s lighter-coloured, shorter, broader and slightly curved and produced by radiation pressure that pushes particles out of the nucleus; this tail of dust and grit shines reflecting sunlight and its curvature is due to the individual dust particles following their independent solar orbit

Question 11

What is a meteoroid?

Answer 11

Small rocky (with maybe some iron-nickel content) irregular lumps of debris in the Solar System that range in size from micrometers to several metres

Question 12

Where do meteoroids originate from?

Answer 12

Some are broken fragments of colliding asteroids whereas others formed through impacts with the surface of the moon or mars-they all orbit the Sun at speeds of up to 40 km/s. A number of meteoroids originate from the dust tails of comets, forming groups called meteoroid streams and are sources of meteor showers

Question 13

What’s a meteor?

Answer 13

Many meteoroids intersect the Earth’s orbit. When they enter our atmosphere, friction causes the meteoroid and surrounding air to heat up producing a short streak of incandescent light - a meteor or shooting star

Question 14

What is a fireball?

Answer 14

A meteor with a magnitude of -3 or brighter

Question 15

What is a meteorite?

Answer 15

A part of a meteoroid that survives its passage through the atmosphere and lands on the Earth’s surface

Question 16

What allows astronomers to classify meteorites into 3 major categories?

Answer 16

Geochemical analysis

Question 17

What are the 3 major categories that meteorites are classified in?

Answer 17

Stones, irons and stoney-irons depending on the ratio of rock to metal

Question 18

What is the radiant?

Answer 18

The point where meteors seem to diverge from this point in the sky even though they are actually travelling parallel

Question 19

How is a meteor shower named?

Answer 19

It is names after the constellation in which the radiant is found

Question 20

What is an NEO?

Answer 20

There are a number of asteroids and comets with orbits that bring them close to that of Earth. Near Earth Objects (NEOs) are those whose trajectory might bring them closer to Earth than 0.3 AU

Question 21

In October 2008, how many NEOs were known?

Answer 21

5600

Question 22

What is a PHO?

Answer 22

A significant proportion of NEOs have projected orbits that might bring them even closer to our planet. These are Potentially Hazardous Objects (PHOs) and they have orbits that bring them closer than 0.05 AU to us.

Question 23

In October 2008, how many PHOs were identified?

Answer 23

1000

Question 24

Name 3 examples of collisions in our Solar System between astronomical bodies.

Answer 24

1. The Moon, several planets and asteroids are covered with impact craters
2. The planets Venus and Uranus rotate on their axis in unusual ways (‘backwards’ and ‘sideways’ respectively). Both are thought to be a consequence of gigantic collisions early in the Solar Systems history
3. The Chicxulub Crater straddling the coast of Mexico (this collision is believed to have caused the mass extinction of dinosaurs 65 million years ago)

Question 25

What size PHOs pose the biggest threat?

Answer 25

PHOs with a diameter of larger than 1 km - these are considered to have enough impact energy to cause a catastrophe on a global scale

Question 26

What is the Torino scale?

Answer 26

It uses numbers to from 0 to 10 based on the likelihood of a collision and the estimated kinetic energy of the impactor. Numbers 0 to 1 indicate likely misses or collisions with objects so small that no damage would ensue. However at the other end of the scale, numbers 8, 9 and 10 refer to what would amount to certain collisions, capable of inflicting localised, regional or world-wide devastation (in the form of land destruction, tsunamis or global climate change that could threaten the future civilisation). It’s in order to categorise impact hazards and communicate potential risks to the public

Question 27

What is a micrometeorite?

Answer 27

A meteorite that can land to the surface without lighting up- becoming incandescent

Question 28

If a PHO hit earth what could happen?

Answer 28

1. So much dust and debris would be thrown up into atmosphere there would be no sunlight - lowering temperatures and perhaps extincting life
2. Super tsunami
3. Disrupt Earth’s tectonic plates

Question 29

At what speed do meteoroids orbit then sun?

Answer 29

40 km/s