Concern for the protection of life on other planets first came about in 1956 when scientists were discussing contamination of the Moon by spacecraft from Earth. When the moon was found to be lifeless, the focus shifted to other places in our solar system where life may exist.

So what are the legal requirements for planetary protection, not only for NASA, but also for other countries? In 1967, the United States and Soviet Union signed a treaty banning the use of nuclear weapons in space, among other things. Article 9 of the Outer Space treaty states that planetary explorations shall avoid, "Harmful contamination" of the Earth and other planets.

The International Council for Space created the Committee on Space Research (COSPAR) so that it could work with NASA and space agencies world wide, to meet space treaty requirements. COSPAR reviews NASA's planetary protection plans and makes recommendations.

According to John Rummel, "COSPAR� had a policy in 1964 that was agreed to by everybody, it's been modified by a series of resolutions and paper citation etc. You end up having to be an archeologist of some kind of a librarian to be able to put the policy together, and then it doesn't all match up in parts and pieces." To fix this situation, Rummel is working with COAPAR's planetary protection committee to draft a new comprehensive policy.

NASA interprets the 1967 Outer Space Treaty requirements as Policy Directive NPD 8020.7E, Biological Contamination Control for Outbound and Inbound Planetary Spacecraft. It states, "The conduct of scientific investigations of possible extraterrestrial life forms, precursors, and remnants must not be jeopardized. In addition, the Earth must be protected from the potential hazard posed by extraterrestrial matter carried by a spacecraft returning from another planet or other extraterrestrial sources."

Any mission that may possibly carry Earth microbes and/or alien microbes is required to follow planetary protection procedures.

NASA's history of planetary protection isn't perfect. NASA's first attempt at planetary protection was the Ranger Moon probe series of the early 1960's. These first Moon probes were designed to crash land on the Moon. The purpose was to get close up photographs of the Moon's surface.

"On missions like the Ranger series that went to the Moon, when we really didn't know how to build a spacecraft that was sterile, we still tried," Rummel says. "And then, once we found out more about the moon we figured out, 'Aw, there's nothing going to grow there.' We were able to fly Rangers that weren't sterile, but yet didn't contaminate. That was a good sign."

NASA's next attempt, the Viking lander program, was much more successful. Even today, planetary protection plans and reports refer to "Viking-level sterilization procedures." The two Viking spacecraft that landed on Mars in 1976 were built in a class 100,000 clean room. This means there were less than 100,000 particles of 0.5 microns or larger per cubic meter. This was a good clean room for the time. But we can do much better than that today. The spacecraft were then heat sterilized to kill the microbes onboard.

John Rummel explains the heat sterilization process; "The Viking missions were baked in an oven for over 50 hours at temperatures over 115 degrees Celsius." That translates to 239 degrees Fahrenheit, or slightly hotter than boiling water.

Engineers did the best they could at that time. They figured that the extreme heat and chemicals were enough to kill anything that might be alive on its surface. Since then, scientists have learned that some microorganisms thrive in boiling water.

What about the inside, the sealed surfaces? Karen Buxbaum, a supervisor of the Jet Propulsion Lab's (JPL) Planetary Protection Technologies Group says, "There is certainly a possibility that Viking might have had spores on the spacecraft that then ended up in the vicinity of the landers."

The U.S. isn't the only country to send probes to Mars and the other planets. The former Soviet Union and Russia have sent several probes to the red planet. Some were successful, some not. There is no way to confirm that the Russian probes went through any sort of decontamination before launch.

"Although the Russians were saying they want to do that, that they intend to do that, and it's their policy to do that - its never really been documented what was done," Rummel says, referring to Russian decontamination policy. "Everything we understand about the way they process payloads would suggest that it would have been very difficult for them to actually have launched the spacecraft that was clean, even if it was cleaned before launch."

As an example, Rummel points to the saga of the 1988 Phobos spacecraft. "I do know that the Phobos launch vehicle was in a room with a bunch of people having a reception before it [was] launched. It's the sort of thing that one wonders whether or not � everything that could have possibly been done for contamination control [had] been done at that point."

Rummel says that Russia's Mars '96 mission followed NASA's planetary protection rules, but only because the French, who were partners on the project, insisted.

The fact that some microbes got by may not be significant. The surface of Mars is a very harsh environment. The thin atmosphere and high radiation levels make it an unfriendly place for most Earth lifeforms.

"One thing that we do understand about Mars is the potential for global contamination event is very small," says Rummel. "Just because it's so cold, so dry, so little atmosphere, that even if there's � water in places, that it's incompatible with the growth and spread of Earth life."

Karen Buxbaum agrees, "The likelihood of any significant amount of contamination from the Viking spacecraft being circulated around the Mars [atmosphere] is very low � the probabilities are so low that � it is a miniscule concern."

The 1996 Pathfinder spacecraft was cleaned to Viking standards, but did not go through the dry heat sterilization that Viking did. This means that there were probably spores left on the spacecraft.

In 1998, NASA launched the Mars Polar Lander and Climate Orbiter spacecraft. Both missions failed and probably crashed into the Martian surface. Both spacecraft were cleaned, but not sterilized. This is because their mission was to look for water, not for life.

"The spacecraft is very clean but not sterile. So yes, there were spores associated with that event, and those would have hit the surface," says JPL scientist Dr. Roger Kern, of the '98 probes. "So we consider that low level of spores associated with a landed event as acceptable." It is "acceptable" because the fiery entry into the Martian atmosphere combined with the harsh environment of the Martian surface is expected to kill microorganisms that may have hitchhiked from Earth onboard the clean spacecraft.

NASA has decided to crash the Galileo probe into the planet Jupiter when its mission is over. The space agency wants to make sure the probe does not crash into one of the moons of Jupiter and cause planetary protection issues. Astronomers suspect that at least one of Jupiter's four largest moons, Europa, may harbor life.

Rummel explains, "The one thing that can be assured is that if Earth life is brought into Jupiter as part of a spacecraft, that before that Earth life would have an opportunity to grow and spread, it would be taken to zones that would kill it, because it's very hot in the lower levels of Jupiter." Jupiter's convection currents would will quickly carry the spacecraft to deep depths and kill any microbes on board.

The 2001 Mars Odyssey Orbiter, which was launched on April 6, 2001, was cleaned, but not sterilized. The craft will arrive at Mars in October 2001. Hopefully, this orbiter won't reach the surface.