Search Results

The search for alien life in the solar system should include exploring unearthlike environments for life having an unearthly biochemistry. We expect alien life to conform to the same basic chemical and ecological constraints as terrestrial life, since inorganic chemistry and the laws of ecosystems appear to be universal. Astrobiologists usually assume alien life will use familiar terrestrial biochemistry and therefore hope to find alien life by searching near water or by supplying hydrocarbons. The assumption that alien life is likely to be based on carbon and water is traditional and plausible. It justifies high priority for missions to search for alien life on Mars and Europa, but it unduly restricts the search for alien life. Terrestrial carbon-water biochemistry is not possible on most of the bodies of our solar system, but all alien life is not necessarily based on terrestrial biochemistry.

Researchers in astrobiology should develop alternate concepts for the detection of extraterrestrial life. We should search for extraterrestrial ecology, exoecology, as well as for extraterrestrial biology, exobiology. Ecology describes the interactions of living things with their environment. All ecosystems are highly constrained by their environment and conform to well-known and inescapable system design principles. An ecology could exist wherever there is an energy source and living things can employ some method to capture, store, and use the available energy. Terrestrial ecosystems use energy sources including light, organic molecules, and, in thermal vents and elsewhere, simple inorganic molecules. Ecosystem behavior is controlled by matter and energy conservation laws and is described by dynamic systems theory. Typically in an ecosystem different molecules are not in chemical equilibrium and scarce materials are conserved, stored, or recycled.

Exobiochemistry is the biochemistry of extraterrestrial life. It describes the potential energy and material basis of extraterrestrial life and is needed to guide the search for alien life. The diverse biochemistry of Earth indicates that a wide range of exobiochemistry is possible on other planets. Any exobiochemistry we discover will probably use the same energy sources as Earth's natural biochemistry - light, biological organic material, and more rarely abiotic chemicals. Extraterrestrial life will be based on familiar chemical principles and so will probably capture, store, and release energy using oxidation-reduction reactions similar to those found on Earth. Any extraterrestrial life must produce some chemical indication of its existence. Useful elements will be concentrated, stored, and recycled, altering their availability and isotopic composition.

Popular depictions of space exploration as well as government life support research programs have long assumed that future planetary bases would rely on small scale, closed ecological systems with crop plants producing food, water, and oxygen and with bioreactors recycling waste. In actuality, even the most advanced anticipated human life support systems will use physical/ chemical systems to recycle water and oxygen and will depend on food from Earth. This paper compares bioregenerative and physical/chemical life support systems using Equivalent System Mass (ESM), which gauges the relative cost of hardware based on its mass, volume, power, and cooling requirements. Bioregenerative systems are more feasible for longer missions, since they avoid the cost of continually supplying food.