ASTEROIDS

ASTEROIDS

Asteroids are small, atmosphere-less rocky-metallic objects which range in size from about the size of pebbles to around 600 miles (~1,000 km) across (Ex - Ceres). Although they orbit the Sun, they are too small to be considered planets. Asteroids are thought to be leftover material from the formation of our Solar System. While dust particles came together to form celestial objects through a process called accretion – smaller objects came together with other small objects, creating larger space rocks. Some of these celestial rocks were able to grow large enough to develop their own gravity and became planets. Many others were held back from getting together by Jupiter's gravitation force. These became asteroids.

Because they revolve around the Sun like planets do, asteroids are also sometimes called planetoids or minor planets.

                    an asteroid.

Most are found in the Asteroid Belt, a doughnut-shaped ring which lies between the orbits of Mars and Jupiter and in the Jupiter Trojans. Astronomers have also identified a group of asteroids whose orbits cross Earth's orbit, termed as near-Earth asteroid. Several hundred thousand asteroids are known to exist in our Solar System, and many are yet to be discovered. Most of the undiscovered asteroids are the smaller ones (less than 100 km across) which are more difficult to detect. It is estimated that there are over a million of these smaller asteroids.

                                            Ahead of Jupiter is Greek camp and behind is Trojan Camp.

Depending on the chemical component, which is the carbon content, metal composition and silicate quantity, the asteroids are classified into 3 main groups:

1) C-type or  carbonaceous asteroids  – These are the most common type of asteroids, consisting 75% of known asteroid population, also dominating the outer part of asteroid belt. All carbonaceous asteroids fall under this category. C-type asteroids are extremely dark in their nature with their reflection co-efficient ranging from 0.03 to 0.10.

2) S-type or silicaceous asteroids – The moderately-bright asteroids (albedo/reflection co-efficient- 0.10-0.22) with component mainly including iron and magnesium silicates. These are mainly found in the inner asteroid belt.

3) M-type or metallic asteroids– The asteroids with nickel and iron in its purest form are categorised under M-type. Sometimes these are also found with the presence of stones. Their brightness ranges from 0.1 to 0.2. These are found in the middle of the Asteroid Belt and are much brighter.

All the asteroids are visible by binoculars except for one, Vesta because of the relatively reflective surface. It is only rare that a passing asteroid becomes visible to naked eyes.

  

Meteoroids

Sometimes one asteroid can smash into another. This can cause small pieces of the asteroid to break off. Those pieces are called meteoroids.

                                                                  Meteors

If a meteoroid comes close enough to Earth and enters Earth’s atmosphere, it vaporizes and turns into a meteor: a streak of light in the sky.

Because of their appearance, these streaks of light are sometimes called "shooting stars." But scientists know that meteors are not stars at all—they are just bits of rock!

At certain times of the year, you might be lucky enough to see more meteors in the sky than usual. This is called a meteor shower.  Image credit: NASA/JPL

Because meteors leave streaks of light in the sky, they are sometimes confused with comets. However, these two things are very different.

Comets

Comets orbit the Sun, like asteroids. But comets are made of ice and dust—not rock.

As a comet’s orbit takes it toward the Sun, the ice and dust begin to vaporize. That vaporized ice and dust become the comet’s tail. You can see a comet even when it is very far from Earth. However, when you see a meteor, it’s in our atmosphere.

Meteorites

Sometimes meteoroid rocks don’t vaporize completely in the atmosphere. In fact, sometimes they survive their trip through Earth’s atmosphere and land as rocks on the Earth’s surface. Those rocks are called meteorites.

A scientist investigates a meteorite that landed in Sudan's Nubian Desert in 2008. Image credit: NASA

NASA’s Johnson Space Center has a collection of meteorites that have been collected from many different locations on Earth. The collection acts as a meteorite library for scientists.

Because asteroids formed near at the beginning of our solar system nearly 4.6 billion years ago, meteorites can give scientists information about what the solar system was like way back then!