When Biospheres Collide: A History of NASA's Planetary Protection Program

  • Published

When Biospheres Collide: A History of NASA’s Planetary Protection Program, by Michael Meltzer. US Government Printing Office, 2011, 544 pp.

Even among hard-core space enthusiasts, planetary protection is hardly a well-known concept. However, as Michael Meltzer ably describes in When Biospheres Collide, planetary protection has greatly influenced the American space effort and may prove even more influential in the future. The field of planetary protection attempts to prevent contamination of planetary systems with biology from a different body, keeping “actual or possible ‘zones of life’ pure and unspoiled” (p. 4). In other words, when a space probe is launched from Earth to another space body, planetary protection attempts to prevent “back” contamination (inadvertently releasing microbes or other life from the moon into Earth’s environment) as well as “forward” contamination (transporting unwanted Earth microbes to Mars via unsterilized landers).

Meltzer’s book is a complete survey of planetary protection with sections concerning ethics, law, politics, technologies, procedures, mission histories, and future concerns. The author introduces the ethics and politics of planetary protection first, describing personalities who began the National Aeronautics and Space Administration’s (NASA) program and the issues they confronted. However, much of the book examines planetary protection’s impact on NASA missions. Back contamination dominates the chapter on the Apollo program, in which Meltzer conveys how planetary protection drove many requirements. The latter included adding a multimillion-dollar construction program for biologically sealed facilities to study returned lunar samples, an astronaut-quarantine protocol (including quarantining unfortunate technicians accidentally exposed to lunar samples), and even potentially dangerous steps to astronaut-recovery procedures for the already astronomically complex and expensive moon effort. A chapter on the Viking Mars landers deftly explores problems defending against forward contamination, showing how the Viking program’s search for life could have been fatally compromised by confusing stowaway terrestrial organisms from the lander itself for real Martian life. Later chapters cover the more recent NASA probes, ranging from the Galileo mission to the Jovian planetary system to the famous Mars landers of the early twenty-first century. Throughout the book, Meltzer explains methods of planetary protection considered and used by each mission, including relatively straightforward ones such as dry-heat microbial reduction (cooking the spacecraft) and gas sterilization (flooding the probe with antimicrobial toxic gas). Meltzer also introduces techniques that the uninitiated might not consider, such as choosing toxic propellants (e.g., hydrazine) over fuels that may harbor microorganisms themselves and adjusting orbital trajectories to minimize the probability of unintended collisions with space bodies.

Planetary protection itself may have little direct application, but the book’s glimpse into the psyches of its advocates makes When Biospheres Collide uniquely valuable for military space professionals. Whereas these advocates initially were most concerned about the dangers of back contamination (think Michael Crichton’s The Andromeda Strain), modern proponents now mostly argue against the danger of forward contamination, particularly its potential to damage future space science. Planetary protection proponents often resort to sensationalist language to pursue their agenda. Carl Sagan said that contaminating the moon with terrestrial microbes would be an “unparalleled scientific disaster” (p. 80), and Meltzer himself concludes his work by cautioning that “careless planetary exploration in the present could forever obfuscate the answer to a vital question: Are we Earthlings alone in the universe?” (p. 459). Sold by such dire warnings, planetary protection has had its costs. The author notes that dry-heat sterilization probably caused the very public failures of the early US Ranger lunar probes (p. 50). The all-important gas-chromatograph mass spectrometers designed to search for life on Mars, carried by both Viking landers, eventually failed on Mars. Again, many people blamed heat sterilization for the loss (p. 270). These planetary protection costs may have been worthwhile had they secured the goal of a pristine environment, but Meltzer notes that many unsterilized probes have already crashed, possibly contaminating heavenly targets. The Soviet Venus (Venera 3) probe crashed on Venus and the Zond 2 probe may have done so on Mars—and both may have been understerilized. The NASA Genesis spacecraft went down in Utah, exposing solar wind samples to the open environment, and the Mars Polar Lander crashed near the Martian south-polar ice cap. Back and forward contamination may have already occurred. Meteorites and comets may have been cross-contaminating planets for millennia.

These facts shouldn’t keep us from sterilizing our spacecraft and taking as many precautions as feasible to avoid contamination. Rather, we should do so, knowing that contamination—much like space debris—is probably unavoidable if humans continue to operate in space. We should keep this realization in mind when more radical scientists invoke planetary protection to argue against potentially rewarding endeavors such as human exploration and colonization of Mars or the moon. Instead of taking extreme measures to eliminate the possibility of any contamination (such as avoiding a manned Mars mission), we must find approaches that balance risk with reward and develop ways to clean or otherwise mitigate contaminations that may occur. Meltzer, a planetary protection advocate, argues that “we are accountable to future generations of scientists to explore our solar system without destroying the capability of others to conduct their own investigations” (p. 459). Alternatively, Air Force space professionals know that the American space program is accountable to all members of future generations, not just those who want to be exobiologists.

When Biospheres Collide is surprisingly readable, given its subject. Whether discussing arguments among scientists or the details of technical processes, Meltzer writes in a conversational, illuminating, and enjoyable style. His section on Jupiter’s moons and their capacity for harboring life was particularly satisfying. The narrative seemed to “hiccup” occasionally as he jumped from one subject to another one only indirectly related. These rare events detracted from the book somewhat, but on balance it is very well written. Useful appendices add to Meltzer’s detailed research and quality narrative to make When Biospheres Collide a standard work for anyone studying planetary protection.

Maj Brent D. Ziarnick, USAFR

Reserve National Security Space Institute, Colorado

"The views expressed are those of the author(s) and do not reflect the official policy or position of the US government or the Department of Defense."