When a bunch of leading scientists got together last week to discuss the latest in big thinking, there was no shortage of doomsday predictions. In particular, Earth's fate was painted in three shades of grim.
Sometime in the next few billion years, according to new studies presented at the annual meeting of the American Association for the Advancement of Science, the third rock from the sun will either freeze or fry. Unless things simply dry up much sooner.
The expanding furnace
While Earth's fate is not entirely sealed, predictions of the death of the sun are widely accepted.
The life-giving, aging star we orbit is using up its fuel supply and will collapse within 7 billion years. Before that, though, there will be an agonizing period of repeated swelling, as the sun grows into a red giant. How giant?
"Earth will end up in the sun, vaporizing and blending its material with that of the sun," said Iowa State University's Lee Anne Willson. "That part of the sun then blows away into space, so one might say Earth is cremated and the ashes are scattered into interstellar space."
Willson and her colleague George Bowen studied other red giants, medium-sized stars like our sun that are near death, and used their findings to calculate the fate of Earth.
Artist's conception of the view of a hypothetical planet around a distant red giant star.
As the sun burns its core of hydrogen, gravity will force a collapse. When compacted, the sun will heat up and burn the small amount of hydrogen that remains in a shell wrapped around the star's core. This will force the sun to expand into a red giant. Eventually, the core will heat up enough to burn stored helium and the sun will fluctuate in size before collapsing into a white dwarf.
"Earth will get scorched as part of the process the sun will go through as it transforms from being a red giant into a white dwarf," Willson said.
Out from the frying pan and into the frost
There are two possible paths to salvation, though both involve a frigid end.
"If the sun loses mass before it gets too big, then Earth moves into a larger orbit and escapes," Willson told SPACE.com. "The sun would need to lose 20 percent of its mass earlier in its evolution, and this is not what we expect to happen."
Fred Adams, a University of Michigan physicist, has for a few years been modeling the fate of the entire universe. He said his work agrees with Willson's.
"If Earth stays in its present orbit, its fate is to be fried," Adams said in a telephone interview. "That is the most likely fate."
Meanwhile, Adams has modeled a second possible method of escape.
A less bad scenario
Other scientists have learned that planets around other stars often follow odd-shaped orbits, indicating their paths might have been disrupted by the gravity of a passing star. Adams and a colleague got to wondering whether some future passing star or star system might, in similar fashion, kick Earth into the cosmic hinterlands.
So he and Gregory Laughlin, of NASA's Ames Research Laboratory, simulated many possible encounters with passing stars over the next 3.5 billion years -- assuming Earth would support life at least that long. The odds of the planet being ejected from the solar system, they determined, are one-in-100,000.
"Life on Earth would actually continue longer if Earth is sent out of the solar system than if it stays."
"These aren't real good odds," Adams points out, "but they're greater than the odds of winning the lottery, so they're worth considering."
A report on the work will be published in an upcoming issue of the journal Icarus.
Adams figures if Earth is sent off into some cold cosmic corner, the oceans would freeze solid after about a million years. But some forms of life, supported by hydrothermal vents or other internal energy sources, might continue for up to 30 billion years, he estimates.
"Life on Earth would actually continue longer if Earth is sent out of the solar system than if it stays," he said.
Or, we might just dry up and die
Before Earth's oceans ever have a chance to freeze or fry, they might have already dried up and evaporated into space, said James Kasting, a Penn State professor of meteorology and geosciences. Kasting estimates his version of the end is a mere 1 billion years away.
"The sun is getting brighter with time and that affects the Earth's climate," Kasting said. "Eventually temperatures will become high enough so that the oceans evaporate."
And, Kasting said, a cataclysmic finale may come even sooner. As Earth becomes a global desert, carbon dioxide levels are expected to drop. At a certain level, which he and his colleagues say might be achieved in half a billion years, there would not be enough carbon dioxide to support photosynthesis, and most plants would die.
Remaining plants would not be sufficient to support a biosphere, Kasting contends. So while the entire planet might incinerated in a few billion years, or cast off into a deep freeze, it's possible that life on Earth is already in the sunset years.
"If we calculated correctly, Earth has been habitable for 4.5 billion years and only has a half-billion years left," Kasting said
Thursday, March 13, 2008
Earths Final Sunset
A new calculation predicts that Earth will be swallowed up by the sun in 7.6 billion years, capping off a longstanding debate over whether the sun's gravitational pull will have weakened enough for Earth to escape final destruction or not.
Other theorists have predicted that our planet will fry as the sun expands in its old age. But the time estimates have varied by a couple billion years.
"Although people have looked at these problems before, we would claim this is the best attempt that's been made to date, and probably the most reliable," said astronomer Robert Smith, emeritus reader at the U.K.'s University of Sussex, who made the new calculations with astronomer Klaus-Peter Schroeder of the University of Guanajuato in Mexico. "What we've done is to refine existing models and to put the best calculations we can at each point in the model."
If 7.6 billion years doesn't sound like an urgent death sentence, don't relax yet. Regardless of whether Earth will ultimately be vaporized, as the sun heats up, our planet will become too hot to live on before then.
"After a billion years or so you've got an Earth with no atmosphere, no water and a surface temperature of hundreds of degrees, way above the boiling point of water," Smith told SPACE.com. "The Earth will become dry basically. It will become completely impossible for life of any kind to exist. It's a pretty gloomy forecast."
Nonetheless, scientists are curious about the ultimate fate of our planet after we are gone (like all previous hominids and more than 99 percent of all species that have lived on Earth, humans will probably go extinct, and it will likely happen sooner than a billion years).
Smith's earlier studies found that Earth would narrowly escape being engorged. As the sun ages and expands into a red giant star, it will shed its outer gaseous layers, thus losing mass and weakening its gravitational pull. Previous calculations found that this let-up would allow the Earth's orbit to shift outward, enabling the planet to slip free of the smoldering sun.
But this scenario doesn't account for tidal forces, and the drag of the sun's outer layers. As the Earth orbits the sun, its smaller gravitational pull isn't completely negligible — it actually causes the side of the sun closest to our planet to hoard more mass and bulge out toward us.
"Just as the Earth is pulling on the sun's bulge, it's pulling on the Earth, and that causes the Earth to slow in its orbit," Smith said. "It will spiral back and finally end up inside the sun."
In addition, the gas that the sun expels will also drag Earth inward toward its demise.
Smith's previous calculations had ignored these effects.
"We didn't think it mattered, but it turns out it does," he said. "You might say our previous models had a gap."
There may even be hope for Earth. Some scientists have proposed a scheme for down the road to use the gravity of a passing asteroid to budge Earth out of the way of the sun toward cooler territory, assuming there is life around at the time that is intelligent enough to engineer this solution.
"It sounds like science fiction, but there's a group of people who have quite seriously suggested that it might be possible," Smith said. "If it's done right, that would just keep the Earth moving fast enough to keep it out of harm's way. Maybe life could go on for as much as 7 billion years."
Other theorists have predicted that our planet will fry as the sun expands in its old age. But the time estimates have varied by a couple billion years.
"Although people have looked at these problems before, we would claim this is the best attempt that's been made to date, and probably the most reliable," said astronomer Robert Smith, emeritus reader at the U.K.'s University of Sussex, who made the new calculations with astronomer Klaus-Peter Schroeder of the University of Guanajuato in Mexico. "What we've done is to refine existing models and to put the best calculations we can at each point in the model."
If 7.6 billion years doesn't sound like an urgent death sentence, don't relax yet. Regardless of whether Earth will ultimately be vaporized, as the sun heats up, our planet will become too hot to live on before then.
"After a billion years or so you've got an Earth with no atmosphere, no water and a surface temperature of hundreds of degrees, way above the boiling point of water," Smith told SPACE.com. "The Earth will become dry basically. It will become completely impossible for life of any kind to exist. It's a pretty gloomy forecast."
Nonetheless, scientists are curious about the ultimate fate of our planet after we are gone (like all previous hominids and more than 99 percent of all species that have lived on Earth, humans will probably go extinct, and it will likely happen sooner than a billion years).
Smith's earlier studies found that Earth would narrowly escape being engorged. As the sun ages and expands into a red giant star, it will shed its outer gaseous layers, thus losing mass and weakening its gravitational pull. Previous calculations found that this let-up would allow the Earth's orbit to shift outward, enabling the planet to slip free of the smoldering sun.
But this scenario doesn't account for tidal forces, and the drag of the sun's outer layers. As the Earth orbits the sun, its smaller gravitational pull isn't completely negligible — it actually causes the side of the sun closest to our planet to hoard more mass and bulge out toward us.
"Just as the Earth is pulling on the sun's bulge, it's pulling on the Earth, and that causes the Earth to slow in its orbit," Smith said. "It will spiral back and finally end up inside the sun."
In addition, the gas that the sun expels will also drag Earth inward toward its demise.
Smith's previous calculations had ignored these effects.
"We didn't think it mattered, but it turns out it does," he said. "You might say our previous models had a gap."
There may even be hope for Earth. Some scientists have proposed a scheme for down the road to use the gravity of a passing asteroid to budge Earth out of the way of the sun toward cooler territory, assuming there is life around at the time that is intelligent enough to engineer this solution.
"It sounds like science fiction, but there's a group of people who have quite seriously suggested that it might be possible," Smith said. "If it's done right, that would just keep the Earth moving fast enough to keep it out of harm's way. Maybe life could go on for as much as 7 billion years."
Subscribe to:
Comments (Atom)
