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article imageThe Sun Will Eventually Engulf Earth

By Chris V. Thangham     Sep 8, 2008 in Environment
The Sun will expand to a size that will overlap Earth’s orbit and shine 3,000 times brighter in 7.6 billion years. This will spell doom for many planets including the Earth in our Solar system.
A British mathematician came up with this theory in 1924, believing the Sun’s red giant phase will expand and eventually envelop Earth.
Recently, Dr. Robert Smith, Emeritus Reader in Astronomy at the University of Sussex, and his team calculated this expansion theoretically, showing how the sun will lose mass initially and reduce the gravitation pull on the Earth, allowing the Earth’s orbit to move outward in 7.6 billion years. However, some of the orbit will fall on the outer layers of Sun’s atmosphere and that will reel the Earth in until it is vaporized by the sun.
You can see the animation of this process here.
Most scientists agree with this theory, but they disagree about what will happen to Earth. Some say Earth will be vaporized, while others say that it will escape vaporization.
Some believe when sun expands beyond Earth’s orbit, it will lose quite a bit of its mass and will have less gravitational influence on the Earth over time. When the sun reaches its maximum radius of 1.2 AU, it will lose about one-third of its mass. So, they think Earth can escape solar expansion.
Others like Dr. Robert Smith believe Earth will eventually be vaporized after it's pulled into the fringes of the sun’s expanding atmosphere. Forces from other planets are also involved, which will make the whole process even more complicated.
Lorenzo Iorio from National Institute of Nuclear Physics calculated this theoretical expansion of the sun. He used perturbation theory, which simplifies analysis by neglecting small factors and concentrating on the interactions between the sun and earth’s motions. He found that initially the sun’s yearly loss, which is currently about one part in 100 trillion, will remain small until it evolves into the red giant phase. This mass loss will push the Earth outward at about three millimeters a year or about 0.0002 AU. But when the sun reaches its red giant phase, it will balloon up in only a million years to 1.2 AU and thus vaporizing the Earth.
Iorio has submitted this research paper to the journal Astrophysics and Space Science. Several people have doubts about his assumptions and say he ignores the small factors, which may rapidly change in time.
Even if his assumptions are wrong, others like Dr. Robert Smith and Klaus-Peter Schröder of the University of Guanajuato in Mexico, have found similar results with additional factors such as tidal interactions. Based on those calculations, they found any planets that have an orbital radius of less than 1.15 AU will face peril and will ultimately be destroyed.
So can Earth be saved? Don Korycansky of the University of California, Santa Cruz, and his colleagues, think so. They are suggesting a bold proposal to push the Earth away from the Sun by using the gravitational forces of a large asteroid. They said:
...It can be done by harnessing the gravitational effects of a large asteroid that passes by the Earth. The Earth’s orbit is nudged gradually outwards away from the encroaching sun. By doing this incrementally every 6,000 years or so, life on Earth can survive for another 5 billion years and possibly escape the wrath of the sun’s first red giant phase.
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