The Universe and the numerous activities taking place in it has always remained an unsolved mystery. But this statement needs a revision nowadays because scientists and astronomers have started unravelling the secrets of our universe. This article explains one such phenomenon. A team of Astronomers from Armagh Observatory and the University of Buckingham report that discovery of hundreds of giant comets in the outer planetary system over the last two decades means that these objects pose a much greater hazard to life than asteroids.

A significant threat comes from centaurs, giant comets derived from the trans-Neptunian region that reach the inner solar system. Centaurs are cometary bodies, composed of volatile ices as well as silicates, which cross or approach the orbits of one or more giant planets and are therefore dynamically unstable. These centaurs move on unstable orbits crossing the paths of the massive outer planets Jupiter, Saturn, Uranus and Neptune. The planetary gravitational fields can occasionally deflect these objects in towards Earth.

Napier et.al has discussed how the centaurs which are typically 50 to 100 kilometres across, or larger, and a single such body contains more mass than the entire population of Earth-crossing asteroids found to date. Calculations of the rate at which centaurs enter the inner solar system indicate that one will be deflected onto a path crossing Earth's orbit about once every 30,000 to 100,000 years. Whilst in near-Earth space they are expected to disintegrate into dust and larger fragments, flooding the inner solar system with cometary debris and making impacts on our planet inevitable.

With the knowledge gained about these inter planetary matters and the study of how civilisations succumbed and with the continuously changing terrestrial pattern, the geologists have come to a conclusion that a centaur has arrived 30,000 years ago. This giant comet would have strewn the inner planetary system with debris ranging in size from dust all the way up to lumps several kilometres across.

Nowadays hundreds of Centaur and thousands of Trans-Neptunian Objects have been known to exist. This population is increasing on a steady rate. Some of the greatest mass extinctions in the distant past, for example the death of the dinosaurs 65 million years ago, may similarly be associated with this giant comet hypothesis.

With the help of the data sent by the Apollo programme the researchers have also analysed the size and age of lunar craters which is due to the increasing amount of Inter Planetary Dust They also state that the disintegration of giant size comets leave trails and debris ranging from few millimetres to several kilometres. The maxi-mum size of dust aggregate that can belifted from a comet comes from a balance between gravity and sublimation (gas out-flow) pressure; in the case of a comet, say, 50 km in diameter in an Encke-like orbit,metre-sized fragments may be released around perihelion.

Professor Napier comments: "In the last three decades we have invested a lot of effort in tracking and analysing the risk of a collision between Earth and an asteroid. Our work suggests we need to look beyond our immediate neighbourhood too, and look out beyond the orbit of Jupiter to find centaurs. If we are right, then these distant comets could be a serious hazard, and it's time to understand them better."

Its not the end. Its just the beginning of end! Will it really pose a serious threat to our civilisation? Ultimately nature is unpredictable.

Source:

http://www.sciencedaily.com/releases/2015/12/151222082339.htm

Bill Napier, David Asher, Mark Bailey and Duncan Steel. Centaurs as a hazard to civilization. Astronomy and Geophysics, December 2015, vol. 56, pp. 6.24-6.30

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