a . “For decades, astronomers have speculated that debris left over from the formation of the solar system or newly formed from colliding asteroids is continuously falling toward the sun and vaporizing. The infrared signal, if it existed, would be so strong at the altitude of Mauna Kea [Hawaii], above the infrared-absorbing water vapor in the atmosphere, that the light-gathering power of the large infrared telescopes would be overkill. ... In the case of the infrared search for the dust ring, [Donald N. B.] Hall [Director of the University of Hawaii’s Institute for Astronomy] was able to report within days that ‘the data were really superb.’ They don’t tell an entirely welcome story, though. ‘Unfortunately, they don’t seem to show any dust rings at all.’ ” Charles Petit, “A Mountain Cliffhanger of an Eclipse,” Science, Vol. 253, 26 July 1991, pp. 386–387.
u “... interplanetary dust is not highly concentrated around the sun. In situ measurements made with impact detectors aboard the two Helios probes, which reached a heliocentric distance of 60 [solar radii], have also shown that the spatial IDP [interplanetary dust particle] density gradually levels off inside ~100 solar radii.
“Our two-dimensional IR [infrared] observations have shown unambiguously that a prominent circumsolar dust ring did not exist at the time of the 11 July 1991 solar eclipse. Consistent with these results, a second recent IR eclipse experiment also found no evidence of surface brightness enhancements.” P. Lamy et al., “No Evidence of a Circumsolar Dust Ring from Infrared Observations of the 1991 Solar Eclipse,” Science, Vol. 257, 4 September 1992, p. 1379.
b . L. F. Miranda et al., “Water-Maser Emission from a Planetary Nebula with a Magnetic Torus,” Nature, Vol. 414, 15 November 2001, pp. 284–286.
c . In the 1780s, “William Herschel gave planetary nebula their name, because he found that their appearance resembled the greenish disk of a planet.” Sun Kwok, The Origin and Evolution of Planetary Nebula (Cambridge University Press, 2007), p. 1.