Over the past several months, we've written a series of articles speculating about the possibility of extraterrestrial life—on Mercury, Mars, Venus, the Saturnian moons of Titan and Enceladus, the Jovian moons of Europa and Callisto, Pluto and its moon of Charon, and so on. It is improbable that life exists in any of these places, and even more improbable that it exists on the Sun—but scientific progress isn't what happens when our assumptions are confirmed. Scientific progress is what happens when evidence turns an improbable possibility into a probable one. So if we did find life on the Sun, what would it look like?
The idea that life can hypothetically exist on stars is not a new one. In a 1973 article titled "Life on Neutron Stars," astronomer Frank Drake—co-founder of SETI and the person who, with Carl Sagan, designed the Pioneer plaque—described a thought experiment about what life on a neutron star might be like. In a 1987 article for New Scientist, astronomer and sci-fi novelist Robert Forward explored Drake's idea (which formed the basis for his own novel Dragon's Egg) in more detail:
In order to get across to lay audiences that a neutron star was more like a planet than a star, [Drake] speculated that life might exist on its solid surface ...
One can imagine life evolving on a neutron star in the same way as life evolved on Earth. However, the nuclei making up the biological matter ... would not have electrons bound to them, as they do on Earth. Instead, the chemistry producing life depends on nuclear reactions, mediated by the strong force of the nuclei and not on the electromagnetic force responsible for terrestrial chemistry.
An exchange of neutrons would bind the nuclei into "nuclear molecules" in the same way as the exchange of electrons binds atoms into normal molecules. We do not know whether bonding through neutrons would really lead to complex nuclear molecules at these high gravities, but for the sake of telling a story, I assume that they do.
We've actually discovered nuclear molecules. Trouble is that the ones we've observed are unstable and very short-lived, which would seem to preclude the possibility that they could form nuclear elements, much less organic nuclear elements, much less an ecosystem. But if we assume for the sake of argument that ecosystems based on nuclear elements could exist, then there's no reason in principle why they would be limited to neutron stars; it's possible that they would be more resilient to heat than traditional elements, and able to maintain their structure on the surface of a warmer star like our Sun.
Neil deGrasse Tyson was recently asked, in a more general sense, about the possibility of energy-based lifeforms:
INTERVIEWER: "Could an alien species consist of only thought or energy...?"
TYSON (in part): "I don't see why not ... It might be harder to make amorphous life than material life."
And whether we're talking about Drake's nuclear molecules or a different form of energy-based life, that's the problem in a nutshell: it's harder to create anything we would recognize as life without the stability implied by traditional chemistry. We have found no evidence that any form of energy can create analogues to the elements we've familiar with. Until we do, the possibility of life on the Sun—while it remains a possibility—is extremely remote.