American Scientist

To the Editors:

I enjoyed Roald Hoffmann’s Marginalia column “The Thermodynamic Sinks of this World” in your July–August issue. It was a different take on abiogenesis—the origin of life—and the far-from-equilibrium state in which we now find ourselves.

One minor error was incorporated when Hoffmann states, “From a chemist’s point of view, the surface or interior of a star…is boring—there are no molecules there.” Surprisingly, the surface of the Sun (called the photosphere) is relatively cool. Although the solar corona can reach temperatures of 5 million kelvin—and the core’s estimated temperature is three times that—the photosphere is, oddly, a “cool” 6,000 kelvin. This is cool enough to allow molecular species and molecular fragments to exist.

David Nalepa
Cleveland, OH

Dr. Hoffmann responds:

I was mistaken in implying that the surfaces of stars are too hot for molecules to exist. For instance, evidence for H₂O on the Sun was adduced by L. Wallace and others in a study published in Science in 1995. Evidence for H₂ in white dwarf atmospheres was demonstrated by S. Xu, M. Jura, D. Koster, B. Klein, and B. Zuckerman in a 2013 publication in Astrophysical Journal Letters. And molecules are found in abundance in stellar ejecta.