New theory addresses frozen Earth paradox

Published : May 31, 2012 - 10:09 Updated : May 31, 2012 - 10:15

A U.S. scientist says he has a theory why a much fainter sun 2 billion years ago didn't leave a frozen Earth unfit to develop the kind of life we see today.

Why the Earth avoided the deep freeze in what has been dubbed the Faint Young Sun Paradox is a much-debated question among scientists, but Purdue University's David Minton says he believes he might have an answer.

"If you go back in time to about 2 billion years ago, the Earth should have been frozen over," said Minton, citing geological and astrophysical observations that the sun burned at about only 70 percent of its current brightness.

"There's a lot of geological evidence that the Earth wasn't frozen over," the professor of earth, atmospheric and planetary sciences said. "So, what is not equal? That is the Faint Young Sun Paradox."

What was not equal, he proposed, was the Earth's location in relation to the sun.

"I calculated to keep the Earth from being frozen over at the beginning of its history, it would have to be 6 or 7 percent closer to the sun than it is now," Minton said. "It's a few million miles, but from an orbital mechanics standpoint, it's not that far. The question is what could make a planet move from one location to another?"

Minton proposes the Earth may have moved slightly farther from the sun over time through a process called planet-planet scattering, which occurs when one planet or more is ejected from its orbit, an increase in orbital separation occurs, or when planets collide.

"When a planet system or solar system forms there is no knowledge of how long they will be stable. They form and then they can go unstable in some time scale, and that time scale is set arbitrarily," he said.

"Most of the instabilities happen early, and the longer you go in history, the more rare instabilities become. But rare does not mean never, and rare events can happen."

In Minton's theory, two proto-Venus planets existed at one point and went into a chaotic and unstable phase, crossing the Earth's path and boosting it to its present orbit.

The two proto-Venus planets could have then collided, forming the planet Venus that exists today, he said.

(UPI)

<관련 한글 기사>

20억년 전 얼지 않은 ‘지구의 비밀’ 풀렸다

미국의 한 과학자가 20억년 전에 태양이 지금에 비해 상당히 희미하게 빛났음에도 불구하고 지구가 얼지 않고 살아 남은 이유를 밝혀냈다고 말했다.

‘희미한 초기 태양 역설’이라고 불리는 이 시기에 지구가 얼지 않았던 이유는 여전히 과학자들 사이에서 결론이 나지 않고 있지만 퍼듀 대학교의 데이빗 민튼은 답을 찾은 것 같다고 말했다.

민튼은 지질학과 천문학적인 관찰 결과 20억년 전의 태양은 현재 발열량의 70%밖에 발열하지 않았기 때문에 ‘지구는 분명 그 때 얼었어야 했다’고 말했다.

하지만 그는 그 때 당시 지구는 현재 태양으로부터의 거리보다 약 6-7% 정도 가까이 위치해 있던 것으로 추정된다고 말했다.

민튼은 소위 ‘행성대 행성 흩어지기’라고 불리는 과정에서 지구가 태양으로부터 긴 시간동안 살짝 멀어진 것 같다고 했다.

(코리아헤럴드)