And there is Europa, the small moon of Jupiter with an ocean of liquid water. Europa is probably the most likely source of life in our solar system other than the Earth. NASA has plans to send an orbiter and then a lander to search for signs of life in Europa's planet-wide ocean. What is being done to protect Europan life?
How can we seek out life in the solar system without harming it? Can robotic probes built on Earth be made clean enough to search for life on other planets without contaminating it? If we bring samples of alien life back to Earth, how do we prevent them from contaminating Earth's biosphere?
Planetary protection is what experts call the prevention of "cross contamination." That is, preventing life from getting from one planet to another and causing harm. It's an important factor in space exploration that the public is barely aware of, but one that NASA spends a lot of time working on.
Dr. Karen Buxbaum, a supervisor of the Jet Propulsion Lab's (JPL) Planetary Protection Technologies Group says, "There's a certain amount of responsibility that we have as an agency that's doing exploration to not be sort of reckless in dumping stuff in other parts of the solar system."
NASA divides planetary protection concerns into two categories; forward and backward contamination.
Backward contamination is the type of thing that books and movies like H.G. Wells' "War of the Worlds" and Michael Crichton's "The Andromeda Strain" have made popular. It is the contamination of Earth life by alien spores, microbes or organisms.
Science fiction has put the fear of contamination by alien life in our minds. But, what about the reverse? Could our space probes be "infecting" other worlds with Earth life?
It turns out that NASA is working to protect life on other worlds from Earth life, what the space agency calls forward contamination. Buxbaum defines it this way; "Forward contamination refers to contamination of other solar system bodies with biological material from the Earth." But, this concern for alien life remains largely unknown to the American public.
Should we care if we spread Earth life to other planets in our solar system, or anywhere else? NASA cares and that's why the agency has spent over 30 (1967-2001) years and countless dollars trying to prevent cross contamination.
Protecting life on other planets is important business for NASA. It is crucial to the exploration of the solar system. So much so that NASA has created an entire Planetary Protection branch. Dr. John Rummel, NASA's Planetary Protection Officer, works to protect life on Earth and life elsewhere based on NASA's planetary protection policy.
"The policy is actually based on the desire to preserve extraterrestrial environments for the science opportunities that are there," says Rummel.
In other words, if we bring Earth life with us to another planet, there is the chance that we may kill or harm indigenous life. Or, we may make it harder to determine if life ever existed there. We may mistake Earth life for alien life.
"It's in nobody's best interest to obscure that by contamination with Earth organisms," says Rummel. "Nor would you want to discover a wonderful new life form and know that you've killed it Essentially we can meet ethical considerations by the desire to preserve science."
Rummel must approve every NASA space probe before launch. "I often imagine myself strapped to a booster somewhere," Rummel says in a comic voice," 'Now, you won't launch this unless you get my signature.'"
The search for life beyond the Earth has lead to the new science of Astrobiology. Through a combination of many physical and life sciences, astrobiologists seek out life elsewhere in the solar system and the universe. It's important to know where life might be in order to understand where it must be protected. Scientists are only now starting to understand the so-called "habitable zone," the range of environments where life can exist.
Rummel ties astrobiology to planetary protection saying, "The idea of astrobiology [is] to study the origin, evolution, and distribution of life in the universe. And its extremely complementary on one level with planetary protection, in that by preserving the environments in outer space, you give yourself the potential to be able to discover more about them."
On Earth, where there is water, there is life. But life doesn't need water to survive. In the past decade, scientists have discovered "extremophiles", organisms that live in the limits of the Earth's environment. Scientists have found life near hydrothermal vents at the bottom of the ocean, deep inside solid rock, and even at the core of nuclear reactors.
"One of the things that's changed in biology," Rummel says, "Is we've found life in extreme environments on Earth, that are completely different from anything you or I would be comfortable living in. Nevertheless, there would be ample opportunity to have life there. I don't want to live in a boiling pool in the middle of Yellowstone Park, but there are microbes that just love it."
Astronomers have found all the necessary ingredients for life (water, carbon, hydrogen, oxygen and nitrogen) inside clouds of gas and dust floating in deep space. At last count, our solar system has one star, the Sun, 9 planets with 68 moons, and thousands of comets and asteroids. It's quite possible that life arose in at least one of these places.
Detecting life is difficult, and scientists must be careful not to confuse Earth life with alien life. This would risk ruining future life detection experiments. Karen Buxbaum says, "Confusing the scientific results is a threat to the program."
In the near future, NASA plans to use astrobiology to search for life on Mars again. JPL scientist Dr. Roger Kern is planning for such a mission. "What we anticipate will happen with the first landers on Mars is there will be life detection experiments done in-situ, at the site," says Kern. "And those experiments are probably not going to be looking for life, per se, but will be looking for molecules associated with life. So we want to remove as much [Earth life] as possible."
Kern continues, "Where as once NASA was only concerned with sterilizing spacecraft and making sure that the spacecraft couldn't shed a live organism, now we have an interest in seeing to it that it doesn't shed a dead organism as well it kind of takes you into a new definition of clean."
Even with super clean spacecraft, some microbes will always get by. Dr. Rummel says that the current planetary protection plan includes, "An inventory of organic constituents that might be delivered to another body. So that if you happen to go back there and find these things you know that you brought them."
In preparing a spacecraft for launch, technicians take samples of any microbes, spores, or cells on the spacecraft's surfaces. They work to reduce the number of contaminants to as low as possible, cleaning several times if needed.
Talk of planetary protection brings up ethical questions. Dr. Rummel says, "At the present time, NASA's policy for non-contamination of other planets is not based on ethical considerations, although there are many ethical considerations associated with such a thing." Many animal rights activists are concerned about the treatment alien life may receive from Earth probes. Alien life forms, large or small, currently have no rights in current international and national law.
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 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," Kern says 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.
All spacecraft must be cleaned to prevent forward contamination, but this is a straightforward process. Technicians clean the spacecraft and then prove that it is clean by taking samples from the spacecraft. The samples are then studied to find out the number and type of spores, cells, and microorganisms left on the spacecraft.
NASA must use methods other than dry heat for sterilization of today's electronics and other materials. These products make the spacecraft lighter and smaller. This allows for the craft to be launched on today's smaller, cheaper launch vehicles. But these materials can't take the heat. Karen Buxbaum explains, "We have spacecraft materials that are not designed to withstand that type of dry heat environment. So our electronics are incompatible with heating, certain adhesives that we use, some of the optical surfaces, and synthetic materials that we use for spacecraft are ill suited for that type of approach."
Roger Kern agrees, "We can't imagine doing that to a modern spacecraft." This is why research and development efforts are looking into better ways of sterilizing spacecraft parts. Industry sterilization isn't enough. Roger Kern puts it this way, "The science of how to remove bacteria from surfaces is not something that a lot of people have been interested in to the level that we're interested in it. We have to obsess on it."
"What we're doing right now, part of our R&D is to develop and certify sterilization techniques which we can use to supplement the dry heat sterilization process for future missions," says Buxbaum.
One of the cleaning methods that engineers are studying is by using an ultrasonic toothbrush. "One way to look at it is to ask what industry out there would have been concerned with bacteria contaminating surfaces," Kern says. "And of course the dental sciences have been looking at that for a long time."
Preventing forward contamination is easy compared to the risks and difficulties in preventing backward contamination, the contamination of Earth's environment. Karen Buxbaum says this is because, "Back contamination has to do with every element of a project that could add risk to the issues of release of extraterrestrial material into the Earth's biosphere our most demanding challenge in the next decade [is] containment [of samples of alien life]." In other words, it's hard to keep samples of alien life from escaping its container once it is brought to Earth. A mistake could endanger many Earth organisms, including people.
Perhaps the danger to Earth isn't as great as some speculate. The Earth is bombarded by rocks and dust from space every day. John Rummel says, "We get hit by stuff from Mars all the time. My favorite number is 40 kilograms a year, although some of the more enthusiastic people will say tons. It's a big planet. We get hit by one particle per square meter per day. It adds up."
The Mars rock, which was made famous in 1996, may of may not contain fossils of tiny Martians. But, scientists are positive that the rock did come from Mars, because trapped gas pockets exactly match the Martian atmosphere from Viking experiments. It is possible that a rock may arrive with life from Mars. There is no way to tell now if that life would be a danger to us. This is one reason why finding life on Mars is important to scientists. It may be that Mars and Earth exchange rocks, and life all the time. We may have cousins on Mars, and elsewhere.
The largest planet in our solar system is Jupiter. It has many moons, but perhaps the most fascinating is Europa. It has become the most important place in the solar system to scientists looking for life beyond Earth.
Europa is slightly smaller than our Moon. Data from the Voyager and Galileo spacecraft have led scientists to believe that Europa is covered with a thick crust of water ice floating on an ocean of liquid water. Cracks in the crust show that the moon is under constant gravitational stress from the huge planet Jupiter.
Many scientists believe that there may be life in Europa's oceans. But, the moon is bathed in radiation that would kill most Earth life. Life could survive such in the oceans beneath the ice because the thick ice acts as a radiation shield, protecting life in the oceans below.
In June 2000, the Space Studies Board, part of the National Academies, released a report called Preventing the Forward Contamination of Europa. The study concluded that Europa is the most likely place to find life in our solar system and that it must be protected from Earth organisms. It also found that NASA's current planetary protection methods are sufficient to send an orbiting spacecraft to Europa without endangering life in its oceans.
The study noted that microorganisms were able to survive for more than five years in deep space onboard the Long Duration Exposure Facility. So, scientists can't rely on the space journey alone to kill all the microbes.
In permafrost regions of the Earth, extremophiles have been found to survive for millions of years frozen in suspended animation. If a spacecraft were to crash on Europa, it's possible that microbes could survive for centuries until the craft made its way through the ice and reached Europa's ocean.
The radiation field surrounding Jupiter and Europa may help kill off any microorganisms that make it past NASA's planetary protection procedures. But, any organisms that survive and land on the planet could eventually get through the ice and thrive. And spread in the subsurface oceans. Therefore, NASA has made it a policy to be extremely careful about life on spacecraft going to Europa or anywhere in the area of Jupiter, allowing only a one in 10,000 chance of contamination.
Protecting Mars and Europa from Earth life may seem unimportant in our daily lives. But, think about it for a minute. In a century or two we may need these other bodies. Their resources, including possibly its native life forms, if any, may be necessary to understanding how humans can survive on other planets. What do they know about living in a high radiation zone that we need to learn?
However, what if there is life on Mars and WE put it there? Not on purpose, but because we just didn't know better. What we know today indicates that most Earth microbes will not survive on Mars, but it is possible that some could survive and even thrive. We were surprised to find microbes that live in the cores of nuclear reactors. We may be surprised again by the diversity and adaptability of life.
Astrobiology is a new field. If future experiments on Mars do find life, we must be able to tell if it originally came from Earth, or if it is native to Mars. That's why planetary protection is important.
Protecting life on other planets is not a new field. It is one that has advanced as our technology has advanced. Now that the new science of astrobiology has expanded the range under which life can survive, planetary protection is tougher to do and even more important.
Space exploration is a constant trade off. Experts balance the cost of exploration, the potential benefits to humankind, and the risks to both human and alien life. Planetary protection is one of these factors that increases costs, but minimizes risk. Both for us and our alien cousins.
The stuff of life is available in the universe. The question is can we find it without destroying it first.