Message Four (February 18th, 2002)


Bara's brief response


Dear Mr. Bara,

        I am sure that you are familiar with a remark that Arthur C. Clarke made in the letter that he sent to me in September, 1997. It concerns Hoagland's article "The Europa Enigma." Clarke wrote:

"I am also grateful to him [Dick Hoagland] for the excellent 1980 article he wrote--my first introduction to the idea. Since then I have become aware of the fact that many others had thought of it first, as you point out."

        I have often wondered about the "many others" that Clarke refers to in his remark. I never did write back to him to inquire. It is quite possible that he came across the marvelous book "LIFE BEYOND EARTH - The Intelligent Earthling's Guide to Life in the Universe" by Gerald Feinberg and Robert Shapiro, published in Spring, 1980 (William Morrow & Co), which I have no doubt would have been of great interest to him.

        Let me tell you more about that book. Immediately after its publication it was very favorably reviewed by New Yorker Magazine and also received a front-page review in the NY Times Book Review, by Timothy Ferris, where he writes:

"LIFE BEYOND EARTH is one of the best books on Earth about life elsewhere."

        Isaac Asimov also was enthusiastic about the book, writing:

"LIFE BEYOND EARTH is a delightful exercise in daring and imagination. I have never seen life-as-we-do-not-know-it treated with such systematic and rational consideration."

        This book is now out-of-print, but is still frequently found on reading lists for university science courses. It has become something of a classic on the topic. That is not specifically because of the speculations about life within the Galilean satellites, which just takes up a few pages in the book. The authors go far out on a limb in this book, developing their thesis that life can develop under extremely varied sets of conditions and that the conditions they propose should be plentiful in the universe. They present their case carefully and convincingly.

        In their preface, the authors write:

"In this book, we, a physicist and a biochemist, wish to speculate on life as we do not know it. It is not our intent to add to the growing volume of science fiction literature, but to see what can be deduced theoretically from the known laws of science. We have used what is known about life on Earth to infer essential features that any form of life must possess. We then investigate how these general features might express themselves in the specific environments that are found in various parts of the Universe. In other words, we have gone from Earthlife itself to a general definition of life. With this general definition, and a knowledge of the universal laws of physics and chemistry, we then try to imagine what specific types of life can develop in each environment.

        The result of this process is different in some respects from most scientific writing. While much of our book is a straightforward exposition and analysis of known science and its consequences, there are sections, especially in Chapters 8, 12, and 13, where we have been more speculative. We say this not in apology, but rather to indicate to our readers that we are well aware of the different status of these parts of the book.

        In order to carry out this program, even in outline, we have had to tie together many strands from different areas of science. The unsupported knowledge of any two scientists is insufficient to do this. Therefore, we have called on many other scientists and scholars for help. Their assistance has involved instruction in specific areas outside of either of our specializations, descriptions of some of their views on extraterrestrial life, and comments on some of our conclusions."

        Feinberg and Shapiro then go on to thank more than 40 individuals for their assistance. I have quoted from their preface to convey the spirit of the book. The authors took three years to write it. The discussion of the Galilean satellites is in Chapter 10 - "Life on Small, Cool Objects" - which is one of several chapters where the authors apply the conclusions of earlier chapters to specific locations in the Universe.

        I have exchanged a number of messages with one of the authors - Robert Shapiro, a biochemist at NYU, a noted expert on DNA and RNA. More recently, he has written PLANETARY DREAMS, which also explores possibilities of extraterrestrial life. In fact, much of his research concerns the origin of life, and he has proved to be a very original thinker on that topic. (See

        Shapiro attributes the ideas concerning Callisto, Ganymede, and Europa to his co-author Gerald Feinberg. That part of the book was written (at least in the first draft) by Feinberg early in 1979, as they neared completion of their project. According to Shapiro, Feinberg had read about the discovery of the deep-sea vent communities that thrive in the Pacific Ocean. This was his initial inspiration. It was Robert Ballard and his team that made this unexpected discovery in 1977. Feinberg also somehow learned about the predictions of John S. Lewis and the theoretical models developed by Lewis and his student Guy Consolmagno concerning the existence of oceans under a layer of ice on those Galilean satellites. Feinberg realized that Ballard's discovery suggests one possible way in which life might develop in the predicted oceans on those bodies without the benefit of sunlight.

        Only a few pages are devoted to this topic. The discussion is based on the ideas developed in earlier chapters, and especially the concept of "deviation from equilibrium." Altogether, the book makes a fairly convincing case for the existence of life in those predicted Galilean oceans. This is expecially exciting to me because of the recent confirmation that oceans might really exist within all three of those moons. Of course, Europa remains one of the prime candidates for life, partly because of the variety of environmental opportunities it offers. But Ganymede has also been mentioned by scientists in recent years as an interesting candidate. There are indications that extensive geological activity takes place within Ganymede, and the presence of an ocean implies that heat due to radioactive decay within the core is substantial.

        The authors state that Europa, Ganymede, and Callisto are fairly similar to each other, and so they just focus the discussion on Ganymede because it is the largest. Here are some quotes from that discussion.

"Limited information about Ganymede is available from flybys and Earth-based observations. One of the most interesting features is its density, which is quite low compared with that of Earth or Mars. Ganymede must be at least partly composed of much lighter material than the inner planets. It is not large enough to retain hydrogen or helium, and its atmosphere is thin in any event. Water and ice are logical candidates for the lighter material. There is some evidence that Ganymede (and Callisto and Europa) is made of a combination of water and sandlike material, similar to Earth's crust. Various models for Ganymede exist; the one we present is based on the work of John S. Lewis and his collaborators."

"Beneath the ice crust, which is fifty to one hundred kilometers thick, lies an enormous ocean, five hundred kilometers deep. The situation resembles that of our Arctic ocean, but the Ganymede ocean is vaster. There is twenty-five times as much liquid water under the ice of Ganymede as on all of Earth. Below this ocean is the rocky core, at a temperature that varies from 25o C at the bottom of the ocean to several thousand degrees at the center of Ganymede (See Fig. 26)."

"Neither Ganymede's ice surface nor its ocean is pure water. The water contains dissolved impurities of many kinds, just as Earth's oceans do. The precise chemical form of these impurities is unknown, but they may well contain the same elements and simple compounds present in the primitive oceans of our planet. Furthermore, Ganymede's ocean has probably existed in its present form for several billion years. Therefore, this ocean satisfies two of the conditions necessary for life - a suitable material base and enough time for prebiotic and Darwinian evolution to take place."

"The crucial factor which may determine whether life exists in the ocean of Ganymede is whether a suitable energy source has existed to drive the matter away from equilibrium. The water is shielded from the feeble sunlight of Ganymede by the ice crust. It is hard to imagine any useful energy getting through to the ocean from above. However, there is another direction from which energy can reach the ocean - underneath from the hot rocky core. The same radioactive decays that originally melted Ganymede are still producing heat in the core, and this heat works its way out to the ocean in various forms. In order to be of use as an energy source for life, the internal heat must reach the ocean in a concentrated form, such as in a volcanic eruption or an upwelling of hot gas. Otherwise, the heat will just raise the overall temperature at the bottom of the ocean slightly, and will not be available as free energy for life. In our present state of knowledge of the internal workings of Ganymede, we cannot be sure whether rich concentrated energy sources will exist under its ocean. Analogies with Earth would suggest that a significant fraction of the energy would emerge in concentrated form at local hot spots, and at those spots, the deviations from equilibrium that are the beginning of life may occur. (The places on the ocean bottom on Earth where hot springs emerge are rich sites for living creatures. These areas derive their primary energy source from minerals in the hot springs, rather than from the Sun.) The exploration of Ganymede's inner sea will be no easy matter. But the challenge of finding life completely independent of the Sun within the solar system might spur us on to eventually finding a way to look under the Ganymede ice cap."

        The essential point is that some of the geothermal energy produced by radioactive decay in the core should come to the ocean bottom in concentrated form. According to the theoretical discussion earlier in the book (about "deviation from the equilibrium"), that could spur the development of complex chemistry and living things.

        I do not know if this is a reasonable theory. But it does address the crucial question about the Galilean oceans: Can life develop without the benefit of the photo-synthesis which is so crucial to life as we know it on Earth? My own opinion is that the arguments offered in the book are rather encouraging for the possibility that life might exist on all three of those Galilean moons, given the recent evidence that they all may have oceans. Ganymede is my own favorite candidate because there are reasons to believe that the core might exhibit more geological activity than Europa, and there is a likelihood of considerable internal heat.

        Feinberg doesn't explicitly mention one very important point. The deep-sea vent communities discovered by Ballard actually do depend on the dissolved oxygen in the sea-water produced by photo-synthesis near the ocean surface. Therefore, sunlight does play an indirect role in their existence and so these communities are not really an adequate model for life on the Galilean moons. This is something that I learned from Benton Clark's article in LIFE IN THE UNIVERSE (where he offers his own rather specific solution to this problem). Unfortunately, this point is often glossed over in the media. Here is one exception to that:

"Seafloor hydrothermal vents have been suggested as a possible energy source; after all, they support life on Earth. But oxidants are still needed, and in Earth's oceans they migrate down from the surface. No one has figured out where oxidants might originate on Europa."

(From the article "Jupiter's Deadly Radiation Could Power Life On Europa":

        Nevertheless, the reasoning in LIFE BEYOND EARTH does not seem to be weakened at all by this oversight. The basic principles that Feinberg and Shapiro develop in their book would apply perfectly.

        Let me tell you a little more about Gerald Feinberg. If you do a search on the internet, you find that he was an extremely interesting individual. Feinberg was a rather famous elementary particle physicist, noted especially for his work on the hypothetical faster-than-light particles which he called tachyons. He was chairman of the Physics Department at Columbia University, but passed away in 1992 (at the age of 59). He was also an avid science fiction enthusiast and a very early fan of Arthur C. Clarke.

        Gerald Feinberg is not the first to speculate about life in the oceans of the Galilean satellites. As early as 1975, Guy Consolmagno considered this possibility and discussed it with Carl Sagan. Sagan asked the obvious question: How could this happen without sunlight? Duncan Lunan and some of his associates at ASTRA in Scotland also discussed the possibility around the same time. But Feinberg was certainly one of the first individuals to make the link between what happens at the deep-sea vents on Earth and what might happen in the depths of Galilean oceans. Furthermore, the speculations presented in LIFE BEYOND EARTH are worthy of serious consideration because they are based on substantial scientific facts and theories.

        Just as before, this message will be posted on my website. It represents an attempt on my part to remind people of this one interesting and early venture into thinking about life in the moons of Jupiter, and to help remedy the rather unfair situation which I have complained about in the past and which still exists concerning this episode of scientific history.

--Ralph Greenberg