Extraterrestrial Habitats: Yet More Good News

It's a comment I get more often than a shoe shine: "Couldn't we be the first intelligent species in the universe? After all, it took eons to cook up the elements of life -- so maybe we're the first ones out of the gate."

The logic seems believable. After all, we (and our world) are star stuff, as Carl Sagan was fond of saying. But we're not just any star stuff, most of which is humdrum hydrogen and listless helium. Our bodies include fancier ingredients like carbon, oxygen, nitrogen, phosphorous, and a few other herbs and spices. And Earth-like planets are built of this stuff and more (think silicon and iron).

These heavier elements (and they're only "heavy" compared to hydrogen and helium) weren't produced in the hellish fireball of the Big Bang. Rather, they've been slowly roasted into existence deep within the cores of large stars. They became available for fashioning planets and people only when those stars died and belched their chemical-saturated innards into space.

Clearly, enriching the cosmos with heavy elements takes a while. So there's inevitably an interval between the sterile aftermath of the Big Bang and a time when the cosmic, chemistry set had enough ingredients to make rocky planets (and squishy biology). It's that interval that motivates comments about Earthlings possibly being the first out of the gate.

Well, it seems you can stop preening. Despite any inclination to believe yourself among the brightest bulbs around, new research indicates that even when the universe was considerably younger, there were heavy elements enough to spawn planets that could ... spawn life.

A team of astronomers led by Lars Buchhave at the University of Copenhagen has combined data from NASA's Kepler space telescope and instruments on the ground to analyze the prevalence of terrestrial-size worlds. And to everyone's surprise, they find that even so-called "metal-poor" stars are encircled by rocky planets. Metal-poor is just astronomer lingo for "not many heavy elements."

In other words, just as nearly any earthly environment can grow moss, so too can just about any star system grow small, hard planets like Mercury, Mars, Venus and Earth. And these are precisely the type of worlds we feel are best for biology. They've got solid surfaces, and the right chemical ingredients.

All of which has some implications for those of us looking for intelligent life elsewhere.

To begin with, it increases the number of places we might reasonably search. There's no longer any reason to avoid pointing our antennas and telescopes in the direction of star systems that don't have a hefty helping of heavy elements. Just about any star could boast worlds suitable for life. So that's akin to throwing more needles into the haystack.

But there are some other, more subtle benefits.

The central region of the Milky Way, known as the bulge, is stuffed with literally tens of billions of stars. And most of these are old -- considerably older than our Sun or its neighbors -- because this part of the galaxy formed first. Consequently, bulge stars are generally deficient in heavy elements. In the past, SETI researchers would frequently write off such metal-poor 'hoods, assuming that planets there would be as rare as steak tartare. But thanks to Buchhave's new work, there's incentive to aim our radio antennas at these mature central regions, because (1) they could have plenty of planets, and (2) given the high stellar density, we could sample many tens of millions of these star systems with each observation. Sure, the average distance to the bulge is roughly 25 thousand light-years, so signals would be faint. But if you fish with a net instead of a hook, you might have a better chance of landing the big ones.

A second benefit is less obvious, but more interesting. Metal-poor stars are, as noted, frequently older stars. And this could be one of those appealing instances where older is better. Consider: Life arose on Earth close to four billion years ago. Four billion years of slithering, swimming, and soaring life forms. But only in the last 200 thousand years has a species arisen that can fathom the laws of nature, and build hardware able to signal its presence.

In other words, based on the example of Earth, it takes a long time for a planet to incubate intelligent beings

Consequently, metal-poor stars might be better candidates for our SETI experiments because a larger percentage of them might have -- not just life -- but life that's able to build radio transmitters and get in touch.

Will these new results massively change the way we search for E.T? No. But they are one more clue that habitats for intelligent life might be as widespread as kudzu. And of course, where there are habitats, there could be habitants.

You can enjoy panel discussions on science and sci-fi at SETIcon, June 22-24. www.seticon.org