In Lesson 3 & 4, we explore the asteroids, meteors, comets and craters.

In 1989, Asteroid 4581 Asclepius passing through the exact position of the Earth stood only six hours earlier. An impact with Earth would have caused an explosion equivalent to 600 megaton of atomic bomb!

Asteroids are small rocky objects without an atmosphere – airless.

Asteroids varies in size. Some are only a few meters across while some are bigger than a mountain with almost 1,000 km wide!

Image Credit: State Farm / CC BY 2.0

When meteoroids (space debris) enter Earth's atmosphere, it burns up in the upper atmosphere creating a flash of light. This is called meteor, or commonly known as shooting star or falling star.

Most meteors glow in the sky for about a second while some leave behind a glowing trail for as long as a few minutes. Most of them vaporised in the atmosphere without reaching the ground.

Image Credit: Navicore / CC BY 3.0

Comets come from two main sources – the Kuiper Belt and the Oort Cloud.

Comets are similar to giant snowball. The nucleus (center) of comet contains rock and dust, frozen gases (carbon dioxide, ammonia, methane) and ice.

As the comet comes near to the Sun, the nucleus begin to heat up and covered by a coma, a surrounding cloud of gas and dust lifted from the nucleus.

Image Credit: ESO / Sebastian Deiries / CC BY 3.0

Asteroids and comets occasionally collide with planets causing huge crater on the planet’s surface.

Scientists believe that an asteroid with diameter of about 10 km impacted Earth 66 million years ago and led to the extinction of dinosaurs.

Image Credit: D. Roddy, U.S. Geological Survey