Threat From Asteroids

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Jules Verne’s ‘Off on a Comet’ may be science fiction written nearly 150 years ago, in which a Comet touches earth and collects few chunks of it along with people from various nations on a celestial journey for two years. Today, Japan has actually taken out chunks from a real asteroid millions of miles away from earth.

Asteroids or debris left over during the formation of the solar system are a rocky bodies of few feet to several miles in width  found in space.

Most asteroids orbit the Sun between Mars and Jupiter. This “belt” of asteroids follows a slightly elliptical path as it orbits the Sun in the same direction as the planets.

While larger rocks are called asteroids, smaller ones are called Meteorids, which if pulled in by earth’s gravity generally burn out and vaporize before reaching earth and are known as shooting stars. Those that survive the passage and are meteorites.

It is believed by scientists that when an asteroid as large as 10 kilometers across started hit earth in Yucatan peninsula in Mexico some 65 million years ago, it triggered the chain of events that caused the extinction of the dinosaurs.

A few years ago, on February 15, 2013, an asteroid, approximately 20 meters in size created an airburst near Chelyabinsk, Russia, with roughly 20-30 times more energy than was released by the first atomic bombs. Another object, approximately 40-60 meters in size exploded over Tunguska, Russia in 1908, with the equivalent of 5-10 megatons of TNT decimating 2,000 square kilometers of forest.

According to astronomers, the giant planet Jupiter exerting its gravitational force on the asteroids in the belt protects Mercury, Venus, Earth, and Mars from repeated asteroid collisions.

Besides giving us significant clues regarding the origins of our solar system, asteroids can tell us about the evolution of life on earth as there is a strong view among certain sections of scientists that material from asteroids hitting the earth may have had an important role to play in the evolution of life on planet earth.

Asteroids also have the potential to be used for mining ventures by future astronauts as different kinds of metals can be extracted.

Asteroids definitely pose a serious threat to planet earth if their orbital path crosses that of the earth and if the size of the asteroid is huge, the impact on earth of any such collision is likely to be devastating.

The achievement of Japanese space scientists belonging to the Japan Aerospace Exploration Agency has been to be able to create the first-ever artificial crater on an asteroid, Ryugu, to both study rocks underlying the surface to know about the formative period of our  solar system, understanding the origins of life on earth  and also as  a step towards  learning the methodology to blast an asteroid in space in case it is on  collision path or likely to impact earth.

The Japanese Hayabusa 2 probe fired an explosive device on April 5,2019, at the Ryugu asteroid, around 340 million kilometers away from Earth, to blast a crater in the surface and scoop up material.

Scientists are a bit puzzled by the size of the crater because according to their understanding, the crater should have been of 3 metres diameter if the surface was rocky and would be of 10 meters diameter if the surface was sandy. Now, they find that the surface is rocky but the crater created was of 10 metres. Scientists feel that they have yet to understand the scientific principle behind this or there is “something special about Ryugu’s materials”.

 NASA’s Deep Impact probe had also succeeded in creating an artificial crater on a comet in 2005, but it was only for observation purposes.

Ryugu is supposed to have large amounts of organic matter and water from some 4.6 billion years ago around the time of the solar system’s birth.

The mission, with a price tag of around ¥30 billion, was launched in December 2014 from the Tanegashima Space Center in Kagoshima Prefecture and Hayabusa2 reached Ryugu last June. It is scheduled to return to Earth with its samples in 2020.

NASA has a Near Earth Object (NEO) Observations Programme having projects to find, track and characterize at least 90 percent of the predicted number of NEOs that are 140 meters and larger in size.

An impact from asteroids of this size pose a risk to Earth as they would cause large scale devastation. Though no known asteroid larger than 140 meters in size has a significant chance to hit earth for the next 100 years, about 12,500 asteroids presently known are larger 140 metres in size.

A NEO is an asteroid or comet whose orbit brings it into or through a zone between approximately 91 million and 121 million miles from the Sun or within about 30 million miles of Earth’s orbit.

The NEO Observations Program sponsors projects that make use of telescopes around the world to search for NEOs, track them across the sky to determine their orbits, and gain information on their sizes, shapes, and composition.

Then there are ground based Planetary radars which bounce signals off NEOs approaching earth millions of miles away to know their physical shape and track their orbit.

Although the vast majority of NEOs that enter Earth’s atmosphere disintegrate before reaching the surface resulting in more than 100 tons of dust particles.

The Minor Planet Centre operating from  the Smithsonian Astrophysical Observatory, is internationally agreed to be a public archive of small body orbit data submitted by observers around the world.

Wide field telescopes are used to image large parts of the sky to search for objects moving against the background of stars.

The Minor Planet Centre notifies observers worldwide about NEO discoveries so that timely follow up observations can be collected for identification and orbit computation.

It is the Centre for Near Earth Objects Study, which computes the orbit path of NEOs with high precision and provides long term analyses of possible impact on earth if any including impact time and location in the event of a predicted impact.

Interestingly, one can predict impacts sometimes hundreds of years before it may actually happen. The data gathered by CNEOS is also made public.

At the start of 2019, the number of discovered near-Earth asteroids totaled more than 19,000. An average of 30 new discoveries are added each week.

Now-a-days, we have Sentry a highly automated collision monitoring system that continually scans the most current asteroid catalog for possibilities of future impact with Earth over the next 100 years.

 One asteroid that NASA is studying is called Bennu, has a 1/2700 chance of impacting Earth between 2175 and 2195.

The OSIRIS-REx spacecraft presently orbiting Bennu will bring a sample of asteroid material back to Earth after a few years.

There are a few methods that NASA is studying to deflect an asteroid on a course to impact Earth.

One of these techniques is called a gravity tractor  in which a spacecraft would close to the  asteroid and use mutual gravity attraction between the satellite and the asteroid to change the orbital path of the asteroid by certain maneuvers .

Another method is using a  kinetic impactor  where a spacecraft rams into the asteroid at high speed of several kilometers per second to change the course of the asteroid or disintegrate it partially or completely. This method will be used on an asteroid system Didymos in 2022.

Thirdly, nuclear explosive devices can also be effectively used to deflect asteroids particularly if there is hardly any warning time and there is a big asteroid going to impact earth. The X-rays released from a distance above the asteroid will also super-heat and vaporize the upper surface of the asteroid and impart sufficient momentum to the rest of the asteroid pushing it into a new path.

Planetary defense the word itself makes us think of Sci fi movies and alien invasion but the US actually has a Planetary Defence Coordination Office.

Planetary defense is the term used to encompass all the capabilities needed to detect the possibility and warn of potential asteroid or comet impacts with Earth, and then either prevent them or mitigate their possible effects.

The National NEO Preparedness Strategy and Action Plan of USA has estimated that there are over 300,000  known NEOs  larger than 40 meters that could pose an impact hazard and would be very challenging to detect more than a few days in advance.

Asteroids close to and larger than 1 kilometer can cause damage on a global scale. They can trigger earthquakes, tsunamis.

NASA is confident that it has discovered and cataloged all near-Earth asteroids large enough to cause significant global damage and determined that they are not on collision courses with Earth, but there is still some chance objects from the outer solar system could appear and impact the Earth with warning times as short as a few months.

Meanwhile, The International Academy of Astronautics will hold its sixth conference from April 29 to May 3 in College Park, Maryland, USA. The bi-annual conference brings together world experts to discuss the threat to Earth posed by asteroids and comets and actions that might be taken to deflect a threatening object.

Interestingly, a hypothetical asteroid impact scenario will also be presented. The European Space Agency (ESA) has decided to tweet coverage of this  major international asteroid impact exercise live via social media.

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