All about asteroids

On April 15, when we were enjoying a midday nap in India, an asteroid, the size of a football field, quietly flew by the Earth. Known as 2018 GE3, the asteroid flew past at a speed of 1,06,000 kilometres per hour and came as close as 1,92,316 km. This is only half the distance between the Earth and the moon.

This event is of concern because asteroids do have the potential to wreak havoc on Earth. In this week’s Five Ws and One H, we will learn more about asteroids and how they are tracked.

WHATis an asteroid?

Asteroids are space rocks that orbit the sun. They are too small to be called planets and hence they are also called minor planets.

About 4.6 billion years ago, our solar system began when a big cloud of gas and dust collapsed. When this happened, most of the material fell to the centre of the cloud and formed the sun. Asteroids are rocky leftover from the formation of the solar system. They were formed from small pieces of rock and metal.

Asteroids come in different shapes and sizes. They can be irregularly-shaped or near-spherical. They are often filled with crates. The size could be as large as 530 km in diameter and as small as pebbles. The mass of all the asteroids combined is less than that of Earth’s moon, according to NASA. More than 150 asteroids are known to have a moon or two.

WHEREare they found?

Most of the asteroids are found orbiting the sun between Mars and Jupiter, which is the main asteroid belt. Some asteroids, called trojans, share an orbit with a larger planet or moon, but do not collide with it. There are Jupiter, Mars and Neptune trojans. An Earth trojan was also discovered by NASA in 2011. Near-Earth asteroids are those that have orbits close to our planet. As of June 2016, 14,464 near-Earth asteroids are known to exist.

WHATis the difference between an asteroid and a meteor?

Both asteroids and meteors are space rocks. Sometimes, one asteroid may collide with another and break into small pieces. These pieces are called meteoroids. When a meteoroid enters the Earth’s atmosphere, it vapourises and turns into a meteor. You can witness a meteor as a streak of light in the sky. People refer to such meteors as shooting stars. But, remember they are not stars. .

And if a meteoroid enters the atmosphere and falls to the surface of the Earth without vapourising, it is called a meteorite.

HOWdangerous are asteroids to Earth?

As asteroids revolve around the sun in elliptical orbits, they rotate, sometimes tumbling quite erratically.

Asteroids routinely slam into Earth. Space rocks smaller than about 82 feet will most likely burn up as they enter the Earth's atmosphere and cause no damage.

A space rock as big as 2 km (6561 feet) in diameter could cause wide scale devastation across the planet, affecting the climate and leading to the deaths of hundreds of millions of people and species. But such an event could happen only once every 1,000 centuries on average, according to data on NASA website.

WHATare the efforts made to track and study asteroids?

Several missions have flown by and observed asteroids.

In 2001, the NEAR Shoemaker spacecraft landed on Eros, an asteroid near Earth. In 2011, the Dawn spacecraft entered Vesta’s orbit. It successfully completed a 14-month survey of this large asteroid.

In 2016, NASA launched the OSIRIS-REx spacecraft to study a near-Earth asteroid, Bennu. The spacecraft is expected to return a sample of the asteroid to Earth on September 24, 2023, for detailed analysis.

In 2005, the Japanese spacecraft Hayabusa landed on the near-Earth asteroid Itokawa and in 2010, it successfully returned to Earth with a small amount of asteroid dust now being studied by scientists. The Japan Aerospace Exploration Agency (JAXA) launched the Hayabusa 2 probe in December 2014, and plans to return samples from Ryugu in December 2020.

Asteroid Apophis is set to pass by Earth in 2029. It will come as close as 19,400 miles to Earth. The chances of it actually hitting Earth are slim. In March, researchers announced plans for a spacecraft called HAMMER that would collide and knock incoming asteroids in another direction or simply blow them up into tiny pieces.

WHYis it difficult to track asteroids?

Asteroids are small and dark and therefore very difficult to track. They may not reflect enough light for telescopes to easily detect. A near-Earth asteroid also moves quickly in the sky and a telescope will have to look in just the right area, at the right time, to catch it.

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