FEATURE STORY:

The Strange Case of the Iron Sun
An iconoclastic theory of the solar system's origin shows how science tests its truisms.
By Solana Pyne

In the late 1960s, chemist Oliver Manuel made a small but staggering discovery about meteorites. He noticed that the abundances of certain elements in meteorites were distinctly different from those in the Earth and much of the solar system. This observation spurred research showing that our solar system probably formed from material generated in many different stars. For Manuel, it also spawned a radical theory about the origins of our solar system, which he has doggedly pursued for forty years. Nearly all astronomers agree that the Sun and the rest of the planets formed from an amorphous cloud of gas and dust 4.6 billion years ago. But Manuel argues, based on his compositional data, that the solar system was created by a dramatic stellar explosion--a supernova--and that the iron-encased remnant of the progenitor star still sits at the center of the Sun.

Manuel fits a popular stereotype, the lone dissenter promoting a new idea that flies in the face of the scientific establishment. In the real world, some of these theories eventually have been proven right but vastly more have been proven wrong. Manuel is under no illusions about the popularity of his idea. "Ninety-nine percent of the field will tell you it's junk science," he says. The evidence weighs in heavily against him. If he's right, however, we need to completely rethink how planetary systems form. Even if he's wrong, some scientists say, at least he has made people think.

Astrophysicists don't deny the validity of Manuel's original meteorite data. "It was a good observation," says cosmochemist Frank Podosek of Washington University. "This was something we hadn't observed before. It was a fruitful thing to notice, but he picked it up and ran with it very much farther than the basis could justify."

To support his theory, Manuel pieced together bits of information from history, astronomy, biology and physics. He founded his theory on isotopes, variants of an element that have different atomic weights but the same basic chemical properties. On Earth, isotopes have consistent, well-known relative abundances. Manuel cited unusual mixes of isotopes in meteorites and possibly in the atmosphere of Jupiter as evidence that those objects formed from the outer layers of a supernova, where such strange isotope ratios would be the norm. The inner planets, made from rocky debris, formed from heavy elements in the inner part of the supernova, he says, where more familiar isotope concentrations prevailed. And the Sun, which Manuel argues is iron-rich, formed around a neutron star, the collapsed remnant of the exploded star. "This is not a news flash," he says. "This is my conclusion from 42 years of measuring the abundance of isotopes."

Manuel's insistence both infuriates and amuses others in the field. Scientists who know him talk about him in a tone that is both weary and indulgent, as they would describe an eccentric relative. "I happen to like Oliver," says Donald Burnett, professor of geochemistry at the California Institute of Technology. "I don't agree with anything he says, but I find him a colorful character."

There is one widely accepted element in Manuel's scenario. In the universe, many elements heavier than iron are thought to have been forged in supernovae. But the evidence increasingly seems to rule out Manuel's supernova-genesis theory. At the start of the 20th century, many scientists believed the Sun was made mostly of iron. Manuel cites the historical support for an iron-rich Sun as evidence for his theory. "A high iron content for the Sun is not revolutionary but is actually quite compatible with the history of solar research," he says. But in 1925, astronomer Cecelia Payne analyzed the light of our star and proposed that the Sun was most likely a burning ball of hydrogen. By the late thirties, the case was nearly settled. The surface of the Sun has been proven to be mostly hydrogen, and many subsequent studies have led to extremely detailed models of the hydrogen fusion reactions that power our star.

"We can make an explicit model of the Sun, putting its mass and brightness into the computer, along with the laws of physics and that then produces right amount of Sunshine and brightness," says Sallie Baliunas, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics. These models also explain the various stages of stellar evolution that astronomers can observe. And the principles of hydrogen fusion are well established, both in the laboratory and in the detonations of hydrogen bombs. According to theory and experiment, light hydrogen atoms in the Sun fuse together to form helium atoms, releasing bursts of energy in the process. All of the evidence points to our Sun being made primarily of hydrogen.

Manuel argues that the surface is made up mostly of hydrogen only because elements in the Sun separate according to mass. Hydrogen, the lightest element, floats to the surface, while heavier elements huddle below. But his theory creates another problem: If the Sun isn't made of hydrogen, how does it generate its energy? Fusing a heavy and stable element like iron consumes more energy than it releases. In his theory, Manuel relies the neutron star at the center to make up for energy lost when hydrogen is taken out of the picture. The neutrons that make up the star have higher energy than free neutrons, he says, so a neutron escaping from the star releases energy. The free neutron then decays into a proton as it migrates toward the surface, again releasing energy. The proton, which is a hydrogen atom minus an electron, fuses to form helium and releases even more energy. He supposes that some of the decayed neutrons stick around as protons and account for the abundance of hydrogen on the surface of the Sun and in the solar wind. Manuel's colleagues are skeptical about this elaborate and unproven explanation.

Many scientists also find it improbable that our solar system could have formed quickly from the debris of a supernova. They have only found one system in which planets formed around a neutron star, and it looks nothing like our solar system. On the other hand, astronomers have spotted innumerable stars forming out of clouds of gas and dust and find strong indications that planets are forming around these protostars.

Finally, there is persuasive evidence that our solar system contains the remains of many different supernovae. Ironically, Manuel's own discovery contributed to this understanding. Chemists have traced the strange isotopic concentrations Manuel first observed to individual grains within meteorites. The proportions of each isotope vary from grain to grain. If the solar system formed from a single supernova, all the grains should have roughly the same abundances of isotopes. Since they don't, most scientists view the isotopes in a particular grain as a clue to its origin, and, hence, as evidence that meteorites, and most other bodies in the solar system, are made of heterogeneous material derived from many stars. That makes Manuel's theory look less likely than ever. "Fifteen years ago, I would have kept a question mark in my mind," said cosmochemist Roy Lewis, of the Fermi Institute at the University of Chicago. "I would have said well he's almost certainly wrong but by golly if he turns out to be right, won't that be interesting."

Although most scientists don't believe Manuel's theory, they all acknowledge that outlandish hypotheses have been proven correct in the past. It seems especially unlikely in Manuel's case, however. In addition to citing the contradictory evidence, many scientists also dismiss the iron-Sun theory on the grounds of simplicity. Most observations of our solar system can be explained by fairly common processes, so why evoke rare and complicated explanations?

Still, some scientists see fringe theorists like Manuel as an asset, as they make people reassess long-held theories. "Manuel is a little off the wall," Lewis says. "But science is filled with people a little off the wall. Our great strength is to allow them to express their views." Manuel's views got an airing again at the January meeting of the American Astronomical Society meeting in Washington, DC, where once again they received little notice.

Meanwhile, Manuel continues to argue his theory with an air of implacable certainty, believing that solar physics is on the verge of a revolution. He talks as though scientists need only to come to their senses and reassess the data. "I'm not trying to refute the professional careers of the scientists whose shoulders I'm standing on," Manuel says. "My work depends on their evidence. It's just a different interpretation."

— Posted 2/12/02

See Oliver Manuel's site at http://www.umr.edu/~om/ Learn more about how the planets of our solar system formed at http://explorezone.com/space/planets.htm Find out about the elements formed in a supernova at http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/010125a.html Learn about our Sun at http://www.seds.org/nineplanets/nineplanets/sol.html