No. 52: Jul-Aug 1987
L.A. Frank and his associates at the University of Iowa have speculated that the earth is continuously and copiously bombarded by small, icy comets. Not just a few now and then, but a steady rain so intense that over geological time some major geological consequences must ensue. (See SF#44.)
Some observers commented that surely these scientists have thrown away their careers by suggesting something so ridiculous. But the data are there -- in the form of dark spots on satellite images of the earth's dayglow -- and late results continue to support this far-out interpretation, ridiculous or not.
"The mass of these objects is estimated at about 108 gm each, and the total flux is about 107 small comets per year. If this flux is representative of the average flux over geologic time, then the water influx is sufficient to fill the Earth's oceans. The fluxes of these objects are also large for all the planets outside the orbit of Earth. Considerations of thermal stability imply that the fluxes of comets that impact Venus are considerably less. The outer giant planets may be significantly heated relative to solar insolation by the small-comet impacts. For example, the total energy input due both to solar insolation and comet impacts may be similar for Uranus and Neptune. Thus it is possible that the temperatures of these two planets are similar, even though Neptune is farther from the Sun."
(Frank, L.A., et al; "On the Presence of Small Comets in the Solar System," Eos, 68:343, 1987.)
Comment. What has all this to do with "cosmic Gaia"? By "cosmic Gaia" we mean the cosmic version of the conventional Gaia concept; i.e., earth-as-an-organism. The answer is that small icy comets can in principle transport throughout all of space:
In this light, exobiologists need not confine their search for extraterrestrial life to planets surrounding warm suns. Somewhere, far from stars, there may be places where comets may raise atmospheric temperatures to where life can prosper! Sunlight, of course, is not needed absolutely, as demonstrated by the profusion of life around deep-sea vents.