send a few comets in the direction of Earth，and its orbit will be changed. Our world will then be sent spinning into a safer, colder part of the solar system.

　　This idea for improving our climate comes from a group of the

　　US

　　National

　　Aeronautics

　　and

　　Space

　　Administration (NASA) engineers and American astronomers. They say their plan could add another six billion years to the useful lifetime of our planet—effectively doubling its working life.

　　The plan put forward by Dr. Laughlin, and his colleagues Don Korycansky and Fred Adams, needs carefully directing a comet or asteroid so that it passes close by our planet and sends some its gravitational energy to Earth.

　　“Earth's orbital speed would increase as a result and we would move to a higher orbit away from the Sun，” Laughlin said.

　　Engineers would then direct their comet so that it passed close to Jupiter or Saturn. The comet would pick up energy from one of these giant planets. Later its orbit would bring it back to Earth, and the process would be repeated.

　　In the short term, the plan provides an ideal way to global warming, although the term was actually concerned with a much greater danger. The Sun is certain to heap up in about a billion years and seriously compromise our biosphere (生物圈)—by cooking us.

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