The Violent Environs of Early Planets

It's hard not to hope that ET is out there somewhere, waiting for us to discover clear evidence that we are not alone in the universe, but the news these days is a bit discouraging.

If there really is extraterrestrial intelligence somewhere beyond our planet, it doesn't seem to be all that anxious to be discovered. For decades now, scientists and ET enthusiasts have been keeping an ear open to the heavens, expecting to pick up some clue, perhaps a television program, or more likely a radio beacon used for interstellar navigation, that would tell us he, she or it is out there.

But so far, zilch. No deliberate effort to contact us. No slip of the tongue that we might overhear. Nothing.

The latest disappointment comes from scientists who suggest that if ET is out there, he may be having a tough time finding a suitable abode. The research suggests there may be far fewer places out there — planets like our Earth — that could harbor life than we had thought. If that's right, then legions of scientists have erred in telling us for years now that other planetary systems are probably common. And the odds of life existing elsewhere have taken a big hit.

'Planet Stoppers' Keep Numbers Down

These ideas tend to come and go with the rise and fall of tidal waves of information brought to us by such marvels as the Hubble Space Telescope, but over at Vanderbilt University, they are calling the latest finding a "planet stopper." That's tough talk indeed.

It turns out that "stellar nurseries" where new stars are formed are so violent that the dust needed to build planets may be blown away before planets can be formed. Only those new stars shielded from powerful interstellar winds by distance or other bodies would have a chance to form planets.

That means only about one star out of 10 would have any chance of forming a planetary system, according to C. Robert O'Dell, a research professor at Vanderbilt who has spent nearly 40 years studying that most famous of all stellar nurseries, the Orion Nebula.

Here's what many scientists thought was going on:

The Orion Nebula, located about 1,500 light years from Earth, is rich with interstellar clouds of molecular gas. The gas gradually coalesces into new stars in a dramatic process that has long fascinated astronomers. In recent years astronomers have been able to detect rings of dust around some young stars, most notably the nearby star of Beta Pictoris, leading many to conclude that dust left over from star formation routinely forms a flattened disk around the star.

The dust in the disk should gradually coalesce into planets, and it was thought that was a common scenario.

Indeed, when the Hubble was turned toward the Orion Nebula for the first time in 1993, it produced images that indicated that up to 90 percent of the young stars in the nebula were surrounded by "protoplanetary disks," according to O'Dell. That gave great support to the notion that most stars had what it took to build planets.

Dust-Busting Bullies

But when O'Dell and several other scientists took another look at the data, they discovered something quite surprising. The heart of the "stellar nursery" has a number of very young, massive stars that are 100,000 times more luminous than the sun.

These are not the kind of stars you want to trust with your newborn. They are so violent that they send off waves of ultraviolet radiation that should blast the dust to smithereens in a few hundred thousand years, O'Dell told the American Physical Society in Washington this week.

Most experts think it takes at least 10 million years for new planets to form, and therein lies the problem. Before the planets can form, the protoplanetary disk will be wiped out by the hot breath from neighboring big stars.

"It appears that most of the disks will be gone long before planets can form," O'Dell says.

The finding fits neatly with other recent research on the Orion Nebula. A team led by scientists at the University of Colorado at Boulder used the Hubble to study dust particles in the nebula. The researchers found evidence of dusty disks surrounding several young stars similar to our sun, and the dust appears to be clumping together in what would be the first stage of planetary formation.

But like their colleagues at Vanderbilt, the Colorado researchers also found the "nursery" so violent that "it's a hard place to raise a family of planets," says researcher Henry Throop.

The problem, once again, is massive stars that blast their neighbors.

"UV [ultraviolet] light comes streaming off these large stars like a blowtorch, evaporating the gases and removing the dust from the circumstellar dust rings of the smaller stars," Troop says.

Lonely Universe?

That appears to eliminate any chance that most of the stars will form planets, but on the other hand, some stars that were farther away from the bullies seem to be doing quite well. So some of the stars should be able to produce planets, just not nearly as many as had been thought.

So it doesn't mean there aren't any more planets out there like Earth. We know planets can form, because it happened here. But if the latest research withstands the test of time, it may turn out that stars with planets are the oddballs.

And the universe could be a lot lonelier than we might like.

Lee Dye’s column appears weekly on A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.