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Natural sciences

Grade 9

The earth, galaxies and space programmes

Module 16

Comets and other travellers in space

Comets are pieces of ice and rock that travel in orbits around the sun. According to scientists they are remains of matter from the creation of our solar system. However, most of the remains nearest to the sun have been destroyed. Only those in the cold parts behind Neptune and Pluto still exist. They come from an area called Kuiper's Belt.

a comet consists of three parts:

  • A nucleus (mostly rock, ice and carbon)
  • A head, or coma
  • A tail (caused by heating and the reflection of the rays of the sun)

Tail of gasTail of dustNucleusComa

Astronomers are honoured by having a comet named after them if they record such a space traveller for the first time. The comet Hale-Bopp, for example, got its name when Alan Hale and Thomas Bopp spotted and registered it at the same time. In 1997 this comet passed close to the earth and caused great excitement, especially since its nucleus was 40 km in diameter.

Comets travel in oval orbits around the sun. Sometimes when orbits cross, major collisions can occur.

Thus the planet Jupiter was bombarded by fragments from the comet Shoemaker-Levy 9 in July 1994. This was televised and millions of people watched the phenomenon. ( www.dustbunny.com/afk/planets/jupiter/jupimpact.htm )

Halley’s comet was observed in South Africa in 1986. It takes 76 years to orbit the sun.

Comets probably contributed to the formation of our planet and probably also brought carbon and water to our planet.


  • Particles that travel through space are called meteors. When large meteors hit planets, huge craters are caused. The craters on the moon were formed in this way. Some of the largest craters in South Africa are the one at Pretoria and the Tswaing crater, as well as the Vredefort crater in Northwest.
  • Thousands of tons of small meteors usually hit the earth every day, but most are as small as a grain of sand. When they enter the earth’s atmosphere, we call them METEORS, once they have hit the earth’s surface they are called meteorites. Some are large enough to be seen with the naked eye and people call them shooting stars.
  • Meteors as bright as Venus are called fireballs.
  • The largest meteor that has ever hit the earth is known as Hoba. It hit Namibia and weighed about 60 tons. You can still see it near Grootfontein.


  • Asteroids are giant meteors with a diameter of normally up to one kilometre. Approximately 40 000 asteroids revolve around the sun in orbits between the planets Mars and Jupiter, and for this reason this area is called the asteroid belt.
  • Ceres is the largest asteroid and has a diameter of about 1 000 km.
  • Many people believe that an enormous asteroid such as this hit the earth, creating dust clouds that blocked out all sunlight and causing dinosaurs to become extinct 65 million years ago.
  • The last large asteroid hit the earth in Siberia in 1908.
  • Scientists believe that the earth could be hit by an asteroid every few hundred years and so they keep a careful watch on the skies above us.
  • Thousands of amateur astronomers around the world watch faithfully every night and report all “new” objects. These objects are referred to as “near earth objects” or NEOs.
  • It is estimated that there are about a thousand NEO’s in space relatively close to us and that only half of them have been discovered to date.
  • Comets become visible only a few months before they present a danger to us.
  • Marvin Kilgore, an American, currently has the largest collection of asteroid fragments and explains that asteroids have incredible mineral compositions that, if man had the technology, could be mined!

On the web:

Do visit the following websites:




See how the skies above us are monitored by scientists!!

Activity: questions on comets and other travellers in space

1. What is:

a) a comet?

b) an asteroid?

c) a shooting star?

d) a crater?

2. Which comet:

a) collided with Jupiter?

b) was in our skies in 1986?

3. Where are examples of craters found in Southern Africa?

4. Where will you find:

a) Kuiper's Belt?

b) the Asteroid belt?

5. What is the name of the largest asteroid in the asteroid belt?


Did you answer the questions correctly?

[LO 2.4]


LO 2: Constructing Science Knowledge:

The learner will know and be able to interpret and apply scientific, technological and environmental knowledge.

This is evident when the learner:

2.4 applies knowledge.


Comets and other travellers through space


1. a) Blocks of ice and rocks that are in orbit around the sun

b) giant meteorites

c) meteors

d) cavities formed by impact

2. a) Shoemaker- Levy 9

b) Halley

3. Tswaing in the vicinity of Pretoria, Vredefort Dome, Hoba in Namibia

4. a) Kuiper 's girdle – cold regions beyond Neptune and Pluto

b) between Mars and Jupiter

5. Ceres

Questions & Answers

how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
I'm interested in Nanotube
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
can nanotechnology change the direction of the face of the world
Prasenjit Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Natural sciences grade 9. OpenStax CNX. Sep 15, 2009 Download for free at http://cnx.org/content/col11069/1.1
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