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Why most asteroids do not pose a threat to Earth?

Date: 08 September 2020 Tags: Space

Issue

Once every few days, news headlines announce the approach of a new asteroid towards Earth. In reality, a civilisation-threatening risk from space objects is extremely rare– occurring once every few million years.

 

Background

Asteroids are the remnants from the formation of the solar system over 4.6 billion years ago. There are 994,383 known asteroids.

 

Details

  • Asteroids are rocky objects that orbit the Sun, much smaller than planets. They are also called minor planets.

  • Asteroids are divided into three classes. First, those found in the main asteroid belt between Mars and Jupiter, which is estimated to contain somewhere between 1.1-1.9 million asteroids.

  • The second group is that of trojans, which are asteroids that share an orbit with a larger planet. NASA reports the presence of Jupiter, Neptune, and Mars trojans. In 2011, they reported an Earth trojan as well.

  • The third classification is Near-Earth Asteroids (NEA), which have orbits that pass close by the Earth. Those that cross the Earth’s orbit are called Earth-crossers.

  •  More than 10,000 such asteroids are known, out of which over 1,400 are classified as potentially hazardous asteroids (PHAs).

  • Asteroids that are 140 metres or larger (bigger than a small football stadium) are of “the greatest concern” due to the level of devastation their impact is capable of causing.

  • However, it has been pointed out that no asteroid larger than 140 metres has a “significant” chance of hitting the Earth for the next 100 years.

  • Over the years, scientists have suggested different ways to ward off more serious threats, such as blowing up the asteroid before it reaches Earth, or deflecting it off its Earth-bound course by hitting it with a spacecraft.

  • The most drastic measure undertaken so far is the Asteroid Impact and Deflection Assessment (AIDA), which includes NASA’s Double Asteroid Redirection Test (DART) mission and the European Space Agency’s (ESA) Hera.

  • The mission’s target is Didymos, a binary near-Earth asteroid, one of whose bodies is of the size that could pose a significant threat to Earth.

  • Hera, which is scheduled to launch in 2024, will arrive at the Didymos system in 2027 to measure the impact crater produced by the DART collision and study the change in the asteroid’s orbital trajectory.

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