Electrons to Pass the 'White Glove' Over a Spaceprobe
|A thin section of Strain 121, the so-called 'unboilable bug' which survives high-pressure autoclave heating to a record breaking 121 degrees Celsius, or about 250 degrees Fahrenheit. "Growth at 121 C is remarkable," reported discoverers of Strain 121, Lovley and Kashefi, "because sterilization at 121 C, typically in pressurized autoclaves to maintain water in a liquid state, is a standard procedure, shown to kill all previously described microorganisms and heat-resistant spores."
(The white bar equals one micron.) Credit: Derek Lovley, U. Mass., Amherst
Texas A&M nuclear researchers are working with the NASA Jet Propulsion Laboratory to examine how electron beam technology can sterilize spacecraft components.
Dr. Suresh Pillai, director of the National Center for Electron Beam Food Research, and Dr. Lee Braby, a research professor in the department of nuclear engineering, received a grant from NASA to investigate how electron-beam irradiation can contribute to keeping future spacecrafts from seeding other planets and moons inadvertently.
"Deep space missions must be properly sterilized to distinguish between organisms brought from Earth and those that may be indigenous to other planetary bodies, such as Mars," Pillai said in a Texas A&M report. This concern culminated in the wording of the 1967 Outer Space Treaty, which said that nations should pursue studies of solar system bodies "so as to avoid their harmful contamination and also adverse changes in the environment of the Earth."
"Electron-beam irradiation is potentially a better solution than dry-heat sterilization, the key NASA-approved technique," said Pillai. When this method of sterilization is used, electrons are accelerated between two charged anodes and cathodes until they are sufficiently fast to damage the biology of whatever microbes might be tyring to hitch-hike an unwanted extraterrestrial voyage. The technique is already widely used in the plastics and food preservation industries.
NASA's Planetary Protection Program aims to preserve pristine conditions both going outwards and when returning future samples to Earth. John Rummel of the Office of Planetary Protection and Michael Meyer of NASA's Astrobiology Program wrote that Earth is surprisingly hard to wipe off what otherwise might appear to retain its pristine mint conditions. "On Earth," noted Meyer and Rummel, "living organisms are distributed throughout our planet: in rock at depths of over 1,000 meters (about 3,000 feet), in soil frozen for more than 3 million years, in 110-degree Celsius (230-degree Fahrenheit) seawater and so on. Life can reach high abundances in the right environments (a human body contains about 50 percent nonhuman cells, by number, and sheds about 50,000 living cells per day). It is impossible, under normal conditions, to visit Earth and not encounter life." By a similar token, outgoing spacecraft have to be wiped clean using a combination of heat, low-humidity and gamma irradiation in those cases where the electronics are suited for such exposures.
Pillai said dry-heat sterilization involves heating components at 110 C for at least 40 hours. Unlike dry heat, electron beams sterilize at relatively lower temperatures and involve radiation-damage to microbial DNA for the techniques success at preserving spacecraft cleanliness.
|"After living in the dirt of Mars, a pathogen could see our bodies as a comparable host." -John Rummel, NASA Planetary Protection Officer
Image Credit: NASA/Sean Smith
"Unfortunately, many components are heat sensitive and undergo deterioration making them incompatible with heat sterilization," Pillai said.
The research will revolve around heat-sensitive materials such as low-temperature adhesives, polymers used in making lander balloons and printed circuit board materials. The focus will be on developing electron-beam technology for spacecraft materials and components.
"The proposed work will advance electron-beam sterilization technology to an operational level," Pillai said. "This will be a major advance towards adding a new and highly capable sterilization technique to the current limited NASA planetary protection tool set."
NASA's instruction on planetary protection expresses this careful approach to protecting from cross contamination: "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. Therefore, for certain space-mission/target-planet combinations, controls on organic and biological contamination carried by spacecraft shall be imposed in accordance with directives implementing this policy."
Requirements for forward decontamination vary from Category I, for missions to bodies of no biological interest (for example, the Sun), to Category IV, where a spacecraft will land on a planet of potential biological interest. Category V is reserved for missions that visit another solar system body (other than the Moon) and return to Earth.
The Category Five Catastrophe
David Grinspoon, a planetary scientist who spearheaded the Magellan mission to Venus, noted that fictional accounts of space probes spreading microbes into another potentially unprotected biosphere has been a traditional concern. " You may not know it," wrote Grinspoon, "but NASA is guarding you against this danger through the Office of Planetary Protection, which is charged with preventing the inadvertent spreading of life between worlds during space exploration...NASA is also making concerted efforts to prevent 'forward contamination,' in which we would be the evil alien invaders who seed other planets with Earth bugs. NASA crashed the Galileo spacecraft into Jupiter...in an effort to avoid the remote possibility that the spacecraft would one day smash into Europa and cause an unforgivable planetary pandemic on that watery moon. ...[The Mars probes, Spirit and Opportunity] have all been carefully sterilized so that we will not return to Mars one day to find Earthly life forms that we accidentally deposited in an earlier voyage."
The only samples that have been returned to Earth so far have come from the moon. Astronauts on the Apollo missions returned 379 kilograms (835 pounds) of rock and soil from the Moon, and three Russian spacecraft (Luna 16, 20 and 24) also returned moon samples. The samples were kept in sealed containers until they arrived at their respective laboratories for study. Some proposals discuss having both the European Space Agency and NASA launch martian sample return missions by 2011, with samples returning to Earth by 2016.
|Tiny earth, a planet that could be blotted out with a lunar astronaut's thumb.
Sample return missions currently in progress include spacecraft designed to sample a comet, an asteroid, and the solar wind. Although life is not likely to be found in these places, the precursor chemicals that make life possible may be present.
NASA's Stardust mission, launched in 1999, will reach comet Wild 2 in January 2004. Stardust will return to Earth with both cometary and interstellar dust particle samples in January 2006.
NASA's Genesis mission was designed to collect solar wind samples. The spacecraft was launched in August of 2001 and has now collected particles coming off the sun. The samples will be returned to Earth in September 2004.
Japan's MUSES-C spacecraft, launched May 2003, is headed for asteroid 1998 SF36. After its arrival in June 2005, the spacecraft will gather up to one gram of material from a variety of sites on the asteroid. The samples are expected to arrive back on Earth by June 2007.
In looking forward to these and other missions, any addition to the tools available for handling life's bountiful productivity may broaden the kinds of future space hardware that passes our own planet's ultimate 'white glove' test.