"The trouble with most folks isn't so much their ignorance. It's know'n so many things that ain't so." - A favorite quote of Richard A. Muller, by 19th century humorist Josh Billings.
When you think big, as Richard A. Muller does, you're bound to create ideas now and then that are so compelling you just can't let go of them -- ideas so outlandish that mainstream scientists are equally eager to dismiss them.

Muller, a physicist at University of California at Berkeley, has had his share of big ideas.

If you don't count the restaurant he owned between 1976 and 1982 ("If anyone near and dear to you wants to open a restaurant, I can now be hired to talk them out of it."), Muller's ideas are generally rooted in solid science and genius extrapolation. He's got a gaggle of prestigious awards to prove it, with titles that say things like "outstanding" and "highly original."

But Muller's biggest idea is a real Nemesis. Or so he claims.

Like a thorn in the side of mainstream researchers, Muller's Nemesis theory -- that our Sun has a companion star responsible for recurring episodes of wholesale death and destruction here on Earth -- seems to reemerge periodically like microbes after a mass extinction.

It's a theory that has many detractors. And it's a theory that has been beaten down and left for dead in the minds of most scientists.

Yet it is a theory that just won't die.

Nemesis is cautiously supported by a handful of scientists, who often sound like ringside rooters eager for a victory but thankful they don't have to put the gloves on. Muller meanwhile acknowledges the possibility that the whole idea could turn out to be wrong, but he is nonetheless confident that Nemesis will be found within 10 years.

"Give me a million dollars and I'll find it," Muller said in a recent telephone interview.

Brave words for a bold theory that if proven true would shake up everything we know about the formation and evolution of our solar system.

Genesis of Nemesis

Muller's idea for Nemesis came to him 1983. Luis Alvarez, then an emeritus professor of physics at the University of California at Berkeley, and his son Walter had recently put forth the theory that a giant impact had wiped out the dinosaurs. (This idea, like so many others that are now widely accepted, met with staunch criticism when it was introduced because it, too, was not mainstream).

Around the same time, two other researchers had suggested yet another controversial idea, that mass extinctions occurred at regular intervals -- every 26 million years or so. Scientists immediately folded the ideas into a new and breathtaking possibility: Impacts by space rocks were causing massive global species destruction every 26 million years.

Luis Alvarez was Richard Muller's mentor, and he suggested that Muller try to debunk the periodicity argument. Pondering this, Muller dreamed up the fanciful companion to the Sun as a possible cause, and with Berkeley's Piet Hut and Marc Davis of Princeton, worked out the details.

Muller gave the object the name of the Greek goddess of retribution -- fitting for a killer star that roamed stealthily beyond the solar system flicking comets at dinosaurs.

In the end, the idea looked surprisingly plausible to Muller and his colleagues, and the results of their work were ultimately published in the journal Nature in 1984. Muller then wrote a book about Nemesis, and he has pursued the companion star, while also doing other research, ever since.

Tossing comets at us

Nemesis, as Muller sees it, is a common red dwarf star that would be visible through binoculars or a small telescope, if only we knew which of some 3,000 stars to look at. These are stars that have been cataloged, but their distances are not known.

Any one of them could be the Death Star, as Nemesis has come to be called by some.

Red dwarfs are the most common stars in the galaxy. They are small and relatively cool, dimmer than our Sun. The notion of companion stars is also exceedingly common -- more than half of all stars are part of such a binary system, in which two stars are thought to form out of a single cloud of gas and dust.

Binary stars settle into a gravitational dance around a common point in space. The smaller of the two stars does most of the orbiting, whereas the larger one is much closer to the center of the dance routine. It's like two kids on a seesaw. For the thing to work properly, the heavier child must sit closer to the center of the apparatus.

Muller figures Nemesis' orbit ranges from 1 to 3 light-years away from the Sun.

On its closest approach, the lethal companion would pass through a vast, but sparsely populated halo of primitive comets called the Oort Cloud, which surrounds our solar system from beyond Neptune's orbit out to nearly a light-year away. (The Sun's nearest known star, Proxima Centauri, is about 4.25 light-years away).

During this passage through or near the Oort Cloud, the gravity of Nemesis would scatter a furious storm of primordial comets that had been relatively undisturbed for 4.5 billion years, since the solar system came into being.

Dislodged from their once-stable orbits, millions or billions of these comets would travel to the inner solar system over millions of years, pulled toward the Sun by its gravity. A handful would run into Earth along the way, and the flurry of impacts would result in mass extinctions.

Simple enough. But Nemesis has for years been dogged by a misunderstanding, Muller says. Most researchers think the theory was long ago dismissed by competing data that claimed its orbit was not possible.

Far-out idea

The orbit assumed for Nemesis is an unusual one, Muller admits. No star has ever been found to orbit so far from a companion. "And that really bothers people," he said. "It makes them think that this is a really far-out idea, literally."

But computer models developed by Muller and his colleagues predict that such an orbit must occur at some point in the evolution of most binary star systems. "We just haven't found such systems yet," he said.

And while Muller appreciates the natural and healthy skepticism of other scientists, he figures they are not interested in funding a search because they erroneously assume that Nemesis cannot be found.

Jonathan Tate is the director of Spaceguard U.K., which lobbies for a government response to the threat of asteroids. Tate is among those who see no rush to find Nemesis. He would rather see money spent on more immediate searches for asteroids closer to Earth that might prove to be humanity's undoing in coming decades or centuries.

As Tate points out, proving that mass extinctions occur every 26 million years, regardless of the cause, is only of academic interest: Humans may not likely be around to care, as many researchers don't expect our species to last that long. If we do survive, there will likely be plenty of time to worry.

Questioning periodicity

Meanwhile, many scientists see little or no credibility to the studies alleging periodicity in mass extinctions, and hence no need for a Nemesis theory.

Numerous studies have reported cycles in either impacts or mass extinctions. The period between peaks in these studies mostly range from 26 million to 35 million years. Andrew Glikson of the Australian National University says that trying to pin down things that happened so long ago is no simple challenge. For one thing, space rocks that land in the ocean leave few clues, Glikson points out, and Earth is roughly two-thirds water.

And Earth has always had a crust that is on the move. Evidence gets buried, destroyed, and folded into oblivion by the same process that creates mountains and moves continents.

"Some of the suggested periodicities are more likely to represent statistical artifacts than robust observations," Glikson said.

David Raup, a University of Chicago paleontologist, made the original mass-extinction periodicity argument two decades ago along with colleague J. John Sepkoski. The pair studied marine fossil records over a 250 million-year period that they say showed significant spikes every 26 million years.

"To me, the periodicity idea is as well supported as many ideas that have been adopted into the conventional wisdom, but the scientific community is heartily skeptical," Raup told "Of the 15 or so re-analyses of our data published since the original paper, about half support periodicity and half reject it. It's is still very much in the eye of the beholder."

Muller supports the statistics more emphatically.

"There is a peculiar pattern in mass extinctions, something that cannot be dismissed as a statistical fluctuation," Muller said. "It requires some explanation."

Raup, now retired from active research, would not venture a guess as to when or whether Nemesis might be found, but he expressed hope in the idea: "I am glad Rich [Muller] is still working on it because it may take a lot of effort, and he's the best."

The galactic plane, Planet X and black holes

Other ideas have been put forth to explain the alleged periodicity in mass extinctions.

The most widely accepted is the suggestion that the solar system, as it revolves around the center of the Milky Way, bobs up and down through the plane of the galaxy. This plane is full of gas and dust that never became stars, which collectively has a certain amount of gravity that some expect might dislodge comets from the Oort Cloud.

There are doubts, however, about the amount of mass in the galactic plane and whether or not the timing coincides with the periodicity of mass extinctions.

Others have suggested a dim failed star known as a brown dwarf might be lurking in the distant fringes of the solar system. Muller called the increasing rate of discovery of brown dwarfs, including one that is just 13 light-years away, "extremely discouraging." For if Nemesis were a brown dwarf, it would be harder to find.

Yet another enduring idea is that another large planet lurks beyond Pluto. This so-called Planet X would be a gas ball up to five times the size of Earth, according to some predictions. Even the possibility of a black hole has been raised. Few researchers support these two ideas.

Evidence from the Moon

The best evidence for periodic impacts on Earth may ultimately come from the Moon. While the Earth's crust has been stretched, squashed and folded violently its whole life, the Moon is relatively static, preserving a far more accessible geologic record.

A year ago Muller, Berkeley geologist Paul Renne and then-graduate student Timothy Culler found the Moon underwent a flurry of impacts between 400 million and 600 million years ago. The active period (which may still be going on) presumably affected Earth as well since both bodies are in roughly the same spot in the solar system.

Muller says the sudden increase offers indirect evidence for a sudden change in the orbit of Nemesis, which might have been caused by a passing star.

But the study did not turn up evidence for the 26 million-year periodicity, as hoped. Muller says there was not enough data. The study involved 155 microscopic glass beads formed in the intense heat of lunar impacts and later brought to Earth, in a single gram of soil, by the Apollo 14 crew.

But given that there are "several hundred pounds (kilograms) of [lunar] dust and rocks that have not been analyzed," Muller plans another more detailed study.

Whether or not he finds evidence for Nemesis in Moon dust, it's clear that Muller won't stop looking. He is a man of enduring confidence. But he is also a remarkably conservative scientist, quick as anyone to point out that there is no proof until there is proof.

"I'm realistic," he said. "I may be wrong."

And he recognizes that if the Death Star is not found, the whole idea could become a real Nemesis for the big thinker who dreamed it up.