impediment to life on such a planet: the atmosphere is turbulent, and down deep it is very hot. An organism must be careful that it is not carried down and fried.
To show that life is not out of the question in such a verydifferent planet, my Cornell colleague E. E. Salpeter and I have made some calculations. Of course, we cannot know precisely what life would be like in such a place, but we wanted to see if, within the laws of physics and chemistry, a world of this sort could possibly be inhabited.
One way to make a living under these conditions is to reproduce before you are fried and hope that convection will carry some of your offspring to the higher and cooler layers of the atmosphere. Such organisms could be very little. We call them sinkers. But you could also be a floater, some vast hydrogen balloon pumping helium and heavier gases out of its interior and leaving only the lightest gas, hydrogen; or a hot-air balloon, staying buoyant by keeping your interior warm, using energy acquired from the food you eat. Like familiar terrestrial balloons, the deeper a floater is carried, the stronger is the buoyant force returning it to the higher, cooler, safer regions of the atmosphere. A floater might eat preformed organic molecules, or make its own from sunlight and air, somewhat as plants do on Earth. Up to a point, the bigger a floater is, the more efficient it will be. Salpeter and I imagined floaters kilometers across, enormously larger than the greatest whale that ever was, beings the size of cities.
The floaters may propel themselves through the planetary atmosphere with gusts of gas, like a ramjet or a rocket. We imagine them arranged in great lazy herds for as far as the eye can see, with patterns on their skin, an adaptive camouflage implying that they have problems, too. Because there is at least one other ecological niche in such an environment: hunting. Hunters are fast and maneuverable. They eat the floaters both for their organic molecules and for their store of pure hydrogen. Hollow sinkers could have evolved into the first floaters, and self-propelled floaters into the first hunters. There cannot be very many hunters, because if they consume all the floaters, the hunters themselves will perish.
Physics and chemistry permit such lifeforms. Art endows them with a certain charm. Nature, however, is not obliged to follow our speculations. But if there are billions of inhabited worlds in the Milky Way Galaxy, perhaps there will be a few populated by the sinkers, floaters and hunters which our imaginations, tempered by the laws of physics and chemistry, have generated.
Biology is more like history than it is like physics. You have to know the past to understand the present. And you have to know it in exquisite detail. There is as yet no predictive theory of biology, just as there is not yet a predictive theory of history. The reasonsare the same: both subjects are still too complicated for us. But we can know ourselves better by understanding other cases. The study of a single instance of extraterrestrial life, no matter how humble, will deprovincialize biology. For the first time, the biologists will know what other kinds of life are possible. When we say the search for life elsewhere is important, we are not guaranteeing that it will be easy to find—only that it is very much worth seeking.
We have heard so far the voice of life on one small world only. But we have at last begun to listen for other voices in the cosmic fugue.
* Although traditional Western religious opinion stoutly maintained the contrary, as for example, the 1770 opinion of John Wesley: “Death is never permitted to destroy [even] the most inconsiderable species.”
* In the Mayan holy book the Popol Vuh, the various forms of life are described as unsuccessful attempts by gods with a predilection for experiment to make people. Early tries were far off the mark, creating the lower animals; the penultimate attempt, a near miss, made the
To show that life is not out of the question in such a verydifferent planet, my Cornell colleague E. E. Salpeter and I have made some calculations. Of course, we cannot know precisely what life would be like in such a place, but we wanted to see if, within the laws of physics and chemistry, a world of this sort could possibly be inhabited.
One way to make a living under these conditions is to reproduce before you are fried and hope that convection will carry some of your offspring to the higher and cooler layers of the atmosphere. Such organisms could be very little. We call them sinkers. But you could also be a floater, some vast hydrogen balloon pumping helium and heavier gases out of its interior and leaving only the lightest gas, hydrogen; or a hot-air balloon, staying buoyant by keeping your interior warm, using energy acquired from the food you eat. Like familiar terrestrial balloons, the deeper a floater is carried, the stronger is the buoyant force returning it to the higher, cooler, safer regions of the atmosphere. A floater might eat preformed organic molecules, or make its own from sunlight and air, somewhat as plants do on Earth. Up to a point, the bigger a floater is, the more efficient it will be. Salpeter and I imagined floaters kilometers across, enormously larger than the greatest whale that ever was, beings the size of cities.
The floaters may propel themselves through the planetary atmosphere with gusts of gas, like a ramjet or a rocket. We imagine them arranged in great lazy herds for as far as the eye can see, with patterns on their skin, an adaptive camouflage implying that they have problems, too. Because there is at least one other ecological niche in such an environment: hunting. Hunters are fast and maneuverable. They eat the floaters both for their organic molecules and for their store of pure hydrogen. Hollow sinkers could have evolved into the first floaters, and self-propelled floaters into the first hunters. There cannot be very many hunters, because if they consume all the floaters, the hunters themselves will perish.
Physics and chemistry permit such lifeforms. Art endows them with a certain charm. Nature, however, is not obliged to follow our speculations. But if there are billions of inhabited worlds in the Milky Way Galaxy, perhaps there will be a few populated by the sinkers, floaters and hunters which our imaginations, tempered by the laws of physics and chemistry, have generated.
Biology is more like history than it is like physics. You have to know the past to understand the present. And you have to know it in exquisite detail. There is as yet no predictive theory of biology, just as there is not yet a predictive theory of history. The reasonsare the same: both subjects are still too complicated for us. But we can know ourselves better by understanding other cases. The study of a single instance of extraterrestrial life, no matter how humble, will deprovincialize biology. For the first time, the biologists will know what other kinds of life are possible. When we say the search for life elsewhere is important, we are not guaranteeing that it will be easy to find—only that it is very much worth seeking.
We have heard so far the voice of life on one small world only. But we have at last begun to listen for other voices in the cosmic fugue.
* Although traditional Western religious opinion stoutly maintained the contrary, as for example, the 1770 opinion of John Wesley: “Death is never permitted to destroy [even] the most inconsiderable species.”
* In the Mayan holy book the Popol Vuh, the various forms of life are described as unsuccessful attempts by gods with a predilection for experiment to make people. Early tries were far off the mark, creating the lower animals; the penultimate attempt, a near miss, made the
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