Comets & Meteors Flashcards
Describe cometary orbits.
Comets have what is called inclined orbits, meaning they orbit at a higher (or lower) angle to the ecliptic.
How are cometary orbits different from planetary orbits?
Planets orbit the Sun in a prograde motion. This means they would appear to orbit the Sun anti-clockwise if you were looking at them kilometres above the north pole of the Sun however comets may orbit the Sun in a retrograde motion, the opposite direction to the planets.
All objects orbit the Sun in an ellipse. Planets have a low eccentricity and are more circular. Comets have highly ellipitcal orbits - an oval with the Sun near the very end of one ellipse. They often have parabolic orbits meaning they may not return to the same position again.
Describe the location and nature of the Kuiper Belt and Oort Cloud.
The Kuiper Belt is a region of the Solar System outside the orbit of Neptune. It is thought to extend several times the orbit of Pluto, possibly between 100 to 1000 AU.
The Oort Cloud was suggested as a source of long period comets by Jan Oort. It was thought that comets orbiting the Sun since the creation of the Solar System (over 4,500 million years ago) would have exhausted their supply of ices and other material.
What is the evidence for the existence of the Oort Cloud?
There is no direct evidence for its existence but studies of long period orbits suggest a spherical region at between 10,000 to 20,000 AU that consists of comets that occasionally get disturbed by a passing star and consequently may send comets towards the Sun.
Why do the tails of comets develop when relatively close to the Sun?
The comet gets nearer to the sun and a tail forms in the opposite direction to the Sun. Really this is two tails. A curved dust tail forms and can be up to several millions of kilometres long. This tail forms because of radiation pressure from the Sun.
Particles from the solar wind hit the comet and an ion tail is produced which is more coloured but straighter than the dust tail.
Describe the nature and origin of meteoroids.
A meteoroid is an object in space, possibly simialr to an asteroid that will eventually become a meteor.
Describe the nature and origin of meteorites.
If a meteor survives the entry into Earth’s atmosphere it will land as a meteorite.
Describe the nature and origin of micrometeorites.
A micrometeorite is a micrometre-sized meteorite. There are more micrometeorites that hit Earth than any other type, as there are more in space and also they are too small to be burnt up in the Earth’s atmosphere. Instead, they drift downwards through the atmosphere.
Demonstrate an understanding of meteors.
Meteors are fragments of dust from comets or asteroids that Earth smashes into as it orbits the Sun.
What are the orbits of PHO’s?
PHO’s orbit dangerously close to Earth or will orbit close in the future.
Why do astronomers monitor the motion of potential hazardous objects
A lot of this work is done by amateurs, and scientists campaign for more funds in order to monitor more objects. It is feared that a comet, perhaps returning from the Sun so we cannot see it, or an unseen asteroid may be found that will hit Earth and there may be little time for us to take any action.
