Miércoles 20 de Julio de 2005, Ip nº 118

Hunting for Life in Specks of Cosmic Dust

In astronomy, the race is on to the bottom.

Teams of astronomers are staying up all night in the breath-fogging cold of the high-altitude desert of Chile and in the oxygen-starved heights of Hawaiian volcanoes, deciphering downloaded pixels from the Hubble and Spitzer Space Telescopes over soggy pizza, and then upstaging one another's news conferences, all in the search for the smallest, dimmest crumbs of creation, the most mundane specks of dust that may be circling some garden-variety star.

It is here, in boring, peaceful meadows of the galaxy, far from fountains of lethal high energy particles, swarms of killer comets or hungry black holes, we are told, that we should look if we want to find habitable abodes and possibly life.

And that, of course, would be the most exciting and wonderful result in the history of science, one of the few in astronomy that would probably rebound beyond science, affecting our view of our own status as tenants in this strange house of stars.

Last spring the quest ratcheted another notch downward (or upward) when a team of astronomers announced the detection of a planet only seven times the mass of the Earth circling a dim star named Gliese 876 in the constellation Aquarius. This was the first alien planet that astronomers were unabashedly able to identify as a ball of rock, like the Earth, rather than a bag of gas like Jupiter or Neptune.

Its discoverers estimated that the new planet was made of iron and silicate and was about 70 percent larger in diameter than Earth. Moreover, as in our own solar system, there are larger Jupiter-size planets orbiting Gliese 876 at greater distances.

Never mind for the moment that it was so close to its home star, Gliese 876, that you could bake a lasagna on its surface. The planet was hailed as yet another sign that the cosmos was basically friendly and that sooner or later planet hunters would find worlds as small as Earth out there, another step on the road to finding out whether or not humanity is alone in the universe.

"We are beginning to find our planet's kith and kin among the stars," said Geoffrey Marcy of the University of California, Berkeley, leader of the team that discovered the Gliese planet.

And the joy of family reunion has resounded throughout the cosmos of astronomers for more than 10 years now.

It was on the night of July 4, 1995, that Michel Mayor and his student Didier Queloz woke up their wives at 4 a.m. to drink Champagne and eat raspberry pie at an observatory in the south of France. The astronomers, based at the University of Geneva, had just confirmed that an invisible object about half the mass of Jupiter was sailing around the star 51 Pegasi, tugging it to and fro every four days. It was the first planet ever discovered around another Sun-like star.

Dr. Mayor and his student were using a humble little-used reflector a mere 76 inches in diameter, way small compared with the 320-inch behemoths then being planned and built for cosmology. Their rivals, Dr. Marcy and Paul Butler, professors at San Francisco State, had to make do with similarly unglamorous circumstances at Lick Observatory. "We were typically assigned only two nights per year, exactly when the Moon was full and no one wanted the telescopes," Dr. Marcy recalled in an e-mail message.

Most of the 150 so-called exoplanets subsequently discovered have been found using the "wobble" technique that Dr. Mayor's group and Dr. Marcy's group pioneered. This consists of looking for a to-and-fro motion in the star, induced by the gravitational tug of an orbiting planet.

In retrospect, it seems only natural that the first planetary systems these astronomers discovered were psychotic beasts unlike anything previously imagined. The more massive a planet is and the more tightly it circles its star, the bigger the wobble and thus the easier it is to detect. As a result, the first planets were so-called "hot Jupiters," orbiting their suns in a matter of days instead of years, lethally searing and dense.

As time has gone on and they gather more data on various systems, the observers have been able to detect smaller planets and ones that are farther and farther from their stars, an effect astronomers refer to as "drawing back the curtain."

Last week astronomers announced the discovery of a planet with three suns, in a configuration the theorists had thought was unlikely, if not impossible. Dr. Marcy said in an interview that when the dust finally settled he expected that planetary systems with architectures like our own - with Jupiter-mass planets in circular outer orbits, leaving space for smaller planets in closer orbits protected from comet showers - would be rare, "but not that rare."

Whether those planets will be suitable for life and intelligence is a different matter, however, and one that reaches beyond astronomy into metaphysics and theology. The requirements for Life As We Know It, some astronomers argue, are so exacting that Goldilocks planets like Earth might be rare or even nonexistent.

The list of astronomical requirements for life gets longer and more exacting every year: the home star has to be far enough from the galactic center to be away from lethal black hole pyrotechnics, for example, but not so far into the galactic sticks that stellar evolution has not yet produced enough of the heavier elements like oxygen and iron needed for planets and life.

Among other things, its planet has to have liquid water, a magnetic field to keep away cosmic rays, plate tectonics to keep things stirred, a giant outer planet to keep away comets and asteroids and perhaps a big moon to stabilize its rotation axis.

Of the 200 billion or so stars in the galaxy, what fraction have the lucky combo to win this cosmic lottery? Faced with the same paltry data, different astronomers get vastly different conclusions, ranging from hundreds of thousands to one, namely our own.

Among the various members of the planetary posse, Frank Drake, an astronomer at the SETI Institute and a pioneer of the practice of listening with radio telescopes for alien broadcasts, is one of the most optimistic.

"It may well be that there are far more habitable planets orbiting M dwarfs than orbiting all other types of stars combined," he said on the institute's Web site recently, referring to the dim red stars like Gliese 876. The SETI Institute is holding a conference this week on the habitability of planets belonging to such stars.

On the other hand are pessimists who argue that planets like the Earth and therefore even simple life forms are rare. One is Ben Zuckerman, an astronomer and exoplanet hunter at the University of California, Los Angeles, who admitted in an e-mail message, "Frankly, the correct answer remains anyone's guess, and the range of guesses is very wide indeed."

But, he emphasized, the question can actually be answered by future spacegoing experiments like the Terrestrial Planet Finder and Kepler, which will find and count habitable planets in our corner of the galaxy.

A null result would suggest that humans might be alone in the galaxy or the universe.

This would merely be an interesting academic argument except for a film that is going around, and which I recently viewed, called "The Privileged Planet," which suggests that the Earth's nice qualities are no accident.

The film, produced by Illustra Media in California, is based on a book of the same name by Guillermo Gonzalez, an astronomer at Iowa State, and Jay W. Richards, a philosopher and vice president of the Discovery Institute in Seattle.

It argues that Earth is so special and unlikely that it must be the work of an intelligent designer. "What if it's not a cosmic lottery?" Dr. Richards asks in the film.

The Discovery Institute advocates "intelligent design," a notion that posits the intervention by a designer, whether divine or not, in the origin and history of life, as an alternative to standard evolutionary biology. Illustra Media has produced a series of videos in support of this idea.

The showing of the film at the Smithsonian Museum of Natural History last month exacerbated the worries of many astronomers that the Big Bang would be next on the hit list of creationists.

Thoughtful cosmologists have long wondered about the apparent friendliness of the universe to carbon-based life forms like us. The notion that the fix must be in from a creator, however, has always been rejected as unscientific thinking.

It's the job of scientists, after all, to pursue natural causes and explanations, not settle for supernatural ones.

One such explanation for the specialness of the Earth, for example, comes from theories of modern particle physics and cosmology, which seem to suggest that there have been many, many Big Bangs resulting in a plethora of universes. We live in one that is suitable for us the same way that fish live in the sea.

A prominent cardinal in the Catholic Church, Christoph Schönborn, recently criticized this idea, along with evolution, in a July 7 article on the Op-Ed page of The New York Times. He said the church needed to "defend human reason" against "scientific claims like neo-Darwinism and the multiverse hypothesis in cosmology invented to avoid the overwhelming evidence for purpose and design found in modern science."

But the argument from design, many scientists say, is circular. Charles Stevenson, a planetary scientist at Caltech, said that it was no surprise that the Earth appears suited to our needs. "That's what Darwinian evolution tells us should happen. We are adapted to our world," Dr. Stevenson said.

Who knows what powers atoms in their collective and complex majesty have to respond to their environments over time?

Lacking anything approaching a final theory of physics, or of how planetary systems form, and of more than one example of life - the biosphere on Earth - scientists have no way of actually knowing how unlikely various properties of life and the universe are. In science the smart money is always on surprise.

Everybody agrees that intelligent technological life is much greater leap, but it might be instructive to consider who is laying down bets on at least looking for it. Among the financial angels of the search for extraterrestrial intelligence, or SETI, have been people like Paul Allen, the co-founder of Microsoft; the late Barney Oliver, William Hewlett and David Packard, leaders of Hewlett-Packard; Gordon Moore, the founder of Intel; and the novelist Arthur C. Clarke, who invented the idea of the communications satellite.

The smart money isn't always right, but this is certainly smart money.

  19/07/2005. The New York Times.