[escepticos] Fewer Planets, Less Life? (era: Re: El sentido de la vida y la vida del sentido)

[Carlos del Río <cdelrioc@...>]

    Perdonadme porque la verdad es que en los últimos meses no he
participado mucho, a ver si ahora que estoy de vacaciones...

    Por ahora os envío esto acerca del tema. Ya comentaré algo más.

    Saludos

    Mario

Planeta Escéptica http://www.geocities.com/planetaesceptica




>From ABC News, 3 May 2001
http://abcnews.go.com/sections/scitech/DyeHard/Dyehard.html

Fewer Planets, Less Life?
Fragile Status of Young Planets Suggest ET is Unlikely
By Lee Dye
Special to ABCNEWS.com

May 3 - 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 ABCNEWS.com. A former science writer for
the Los Angeles Times, he now lives in Juneau, Alaska.
Copyright 2001, ABC News