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Jupiter--Earth's Menace or Saviour
Jupiter is the largest planet in our solar system whereas Earth is only the fifth largest among all planets. Jupiter, the massive gas planet, is capable of exerting immense gravitational force on other planets. It is positioned at the sixth orbital position whereas Earth is at the third position from the Sun. The position and gravitational force of Jupiter influences Earth in two ways. On one hand, it is protective, while on the other hand, it is creating problems for our Earth.
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Jupiter as a Menace
Scientists believe that Jupiter's gravitational field is pushing comets and asteroids which are approaching the Earth away from the inner planets, diverting them to the outer planets and thus averting possible catastrophe. Basically, three types of objects, namely, Main belt asteroids, Kuiper belt comets and Oort cloud comets pose a threat to both Jupiter and the Earth. Of these, the Main belt asteroids follow an orbit which is between that of Mars and Jupiter. Kuiper belt comets are found to follow a path which is close to the orbit of the Neptune. Long term comets are known as Oort cloud comets.
The majority of asteroids which hit the Earth are Main belt asteroids. Scientists believe that during the evolutionary stages of the solar system there was a possibility for another planet near Jupiter. But its massive gravitational field prevented the primordial matter near to it from forming another planet . The gravitational field perturbed it in such a way that it started to follow an orbit of eccentricity .33, that is, it moved in to a highly elliptical orbit. As a result of this, many of the primordial material in that orbit collided with the Sun and other solar bodies and thus formed more and more fragments in the early solar system. These fragments are collectively known as the Main belt asteroids. Thus in the absence of Jupiter, most probably, the Main belt asteroids might have joined to form a fifth planet.
A similar situation exists in the case of Kuiper belt objects. Even though the possibility of the Earth being hit by a Kuiper belt objects is minimal, a single one of them wouldn’t have even reached the Earth in the absence of Jupiter. This is because when a Kuiper object falls out of the belt, Jupiter's gravity redirects its trajectory towards the inner solar system.
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Jupiter as a Savior
The situation is quite different in the case of Oort cloud comets. Jupiter plays a major role in diverting these objects away from the inner solar system and thus preventing them from falling into the Earth. In July this year, a massive object hit Jupiter leaving a mark as big as the size of the Pacific ocean on its surface. The scientists who consider Jupiter as a guardian of the Earth point out such incidents to establish the importance of Jupiter as a protector of the Earth. Also, the comets deflected by Jupiter during the evolutionary stages of the solar system are believed to have carried the initial molecules of life to the Earth.
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Jupiter's Two Roles Established
A paper published recently in the International Journal of Astrobiology, J. Horner and B. W. Jones establish these two roles played by Jupiter. Their studies point out the fact that Jupiter’s role varies with the type of object which is approaching us. If it is an Oort cloud comet Jupiter is a saviour. If it is a main belt asteroid or a Kuipler belt comet then Jupiter can act as a terminator of the Earth.
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