Theorizing a Migratory Earth
Earth should be a “snowball planet,” according to common theories of stellar evolution that predict that the sun was only 70 percent of its current brightness when it first lit its fusion engine 4.5 billion years ago. The sun has been steadily growing brighter since then and will continue so into the future, eventually evaporating away Earth’s oceans. Once Earth amassed an ocean 4.3 billion years ago it should have quickly frozen over and reflected so much sunlight back into space that it squelched Earth’s ability to thaw out for billions of years.
The dilemma, called the “faint young sun paradox,” has been know about since the 1950s and was popularized by Carl Sagan. Geochemists and solar physicists have wrestled for answers all these years. Now, David Minton of Purdue University has come up with a novel solution that, by his own admission, straddles science fact and fiction. Minton proposes that Earth was closer to the sun when it formed and then migrated outward to its current orbit. To keep Earth tepid under a cooler sun, our planet would have needed to have been roughly 6 million miles (9.7 million kilometers) closer to the sun than it is today.