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Name: Donnie
Status: Student
Grade: 9-12
Location: MI
Country: United States
Date: March 2006


Question:
How is it known that the sun will eventually destroy the Earth?



Replies:
Donnie,

There are two possibilities:

1) The the Sun will simply cool off and thus the Earth will also.

2) The Sun will explode, possibly in a supernova. In that case the explosion will impact most of the planets in the solar system. The Earth may be destroyed, or just partially destroyed and the remains thrown out of the solar system.

However, neither of these will happen for many millions to billions of years; certainly not within our lifetimes.

David R. Cook
Climate Research Section
Environmental Science Division


Without going into the details (which can be found in many books and/or websites) stars of different masses undergo various stages of their life cycles. That this is the case has been demonstrated by astronomical observations of many star systems. For stars in the mass range of the Sun the primary source of its energy is the conversion of hydrogen into helium. As the Sun "burns" its hydrogen it loses mass (in the form of radiation and high energy particles). The gravitational energy is balanced by the radiation pressure. However, as the supply of hydrogen is depleted, the reduced mass causes the star to increase in size, and to "cool" becoming a red giant star with a diameter that exceeds the distance from the Sun to the Earth. Of course, life would not be able to be sustained long before this actually occurred. That part of the cycle is many millions of years away, so it is of no particular practical interest. The human race has many more potentially catastrophic events and ways to self-destruct long before that becomes an issue.

Vince Calder



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