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International Law & Policy of Extraterrestrial Planetary Protection

by Darlene A. Cypser

Jurimetrics - Journal of Law, Science & Technology

vol. 33 No. 2 pp 315-339 Winter 1993

"...stark and silent...were the Martians--dead!--slain by... bacteria against which their systems were unprepared..., slain, after all man's devices had failed, by the humblest things that God in his wisdom has put upon this earth"

H.G. Wells, War of the Worlds


  1. The History of International Planetary Protection Standards
  2. The Outer Space Treaty
  3. States' Planetary Protection Practices
  4. Post-Viking Exobiology: What is there to Protect?
  5. Questions for the Future
  6. Conclusion


In H.G. Wells' fanciful tale of an alien invasion, humanity was saved when the Martians were killed by terrestrial bacteria. While our native micro-organisms might be handy for destroying extraterrestrial invasion forces, they could also have a devastating effect on less hostile alien life. Even an unmanned space probe landing on another planet could start a microscopic invasion --an invasion that might not only result in the destruction of indigenous life forms on the planet, but destroy the opportunity to study the chemistry and environments of planets that do not yet have any forms of life, or may have had them in the past.

Since the dawn of the Space Age people on Earth have been concerned with the effect that terrestrial microbes from unsterilized spacecraft might have on the environments and potential life forms of celestial bodies. For the most part their concern stemmed from fear that contamination would interfere with future biological and chemical investigations. The value of these environments was seen primarily in their usefulness to science. Few argued for a complete ban on exploration or the creation of planetary "preserves."

Complete sterilization of a spacecraft is impossible, and where there is a single microbe there is a chance of contamination. Sterilization procedures increase the costs of space exploration and are often harmful to components in the craft. Excessive measures would slow the advance of other sciences. Thus it was necessary to develop standards for planetary protection to provide some balance between the need to avoid contamination and the pressures of the drive for greater knowledge.

Throughout the history of the consideration of the problem of contamination by such bodies as CETEX, COPUOS, and COSPAR emphasis has been placed upon the need to protect planets of biological interest for the sake of science. The principle of co-operation in space activities as it has developed under customary international law and the Outer Space Treaty requires that due regard be paid to the interests of other states in the exploration of outer space including the moon and other celestial bodies. This requirement of "due regard" places a duty on states to avoid the harmful contamination of celestial bodies. Biological contamination of a celestial body where life is likely to exist, or where pre-life chemistry is likely to be taking place which would adversely effect other states' programs to study the origins of life is "harmful contamination". National planetary protection policies have evolved in an attempt to meet this requirement. While these policies have been criticized by some as inadequate, they are consistent with current terrestrial international space law which recognizes no absolute protection for alien life forms or alien environments. Limitations are set only on one state's interference with the programs of another state. Once either a planet is determined to be lifeless or the study of the life found has progressed to a certain point, biological contamination of a planet would no longer be considered harmful to the space programs of other states. At that time neither accidental contamination caused by the presence of humans nor intentional implantation of terrestrial life forms would have to be "avoided" under current space law.

Rather than proving or disproving whether life exists on Mars, the Viking experiments (like many scientific experiments) created more questions than there were before. Countless errors in scientific understanding can be traced back to conclusions based upon too little data. The results the Viking lander experiments were bizarre, and while theories abound, these theories cannot be proved or disproved without follow up experiments. Scientific method requires the collection of more data.

The existence of extraterrestrial life is still an open question. Mars continues to be the most likely candidate in this Solar System for finding extraterrestrial life. Renewed interest in the exploration of Mars has prompted the proposal that humans be landed there early in the next century. The landing of humans on Mars is to be preceded by various missions to further explore whether there is life on Mars. However, there is no clear policy as to whether the discovery of life on Mars would inhibit the introduction of humans, or what, if anything would be done to conserve that alien life.

Even if there is no life currently surviving on any other planet in our solar system, there may be traces of past life which would also be an invaluable source of information; a source of information that could be tainted or destroyed once humans carry earth-born microbes to these other worlds.

The current international law and policy on planetary protection is inadequate to meet the challenges of the next quarter century. Should the Cassini Titan Probe be sterilized? What should be done if extraterrestrial life is found? Should human beings set foot on Mars? And what then? These questions and many other questions need both scientific and legal responses. Now is the time to consider these questions and formulate new ethics, policy and law.