Sep. 2, 1998 For a human, unprotected space travel is a short trip measured in seconds.
What could be worse for would-be space travelers than a catastrophic breach in their protective spacesuits, the high-tech, multilayered fabric blanket that balloons under the pressure of a life-saving flow of oxygen and insulates against the frozen harshness of deep-space vacuum?
But for some kinds of microbes, the harshness of space travel is not unlike their everyday stressful existence, the successful execution of ingenious survival tricks learned over billions of years of Earth-bound evolution.
Space historians will recall that the journey to the stars has more than one life form on its passenger list: the names of a dozen Apollo astronauts who walked on the moon and one inadvertent stowaway, a common bacteria, Streptococcus mitis, the only known survivor of unprotected space travel. As Marshall astronomers and biologists met recently to discuss biological limits to life on Earth, the question of how an Earth bacteria could survive in a vacuum without nutrients, water and radiation protection was less speculative than might first be imagined. A little more than a month before the forthcoming millennium celebration, NASA will mark without fanfare the thirty year anniversary of documenting a microbe's first successful journey from Earth.
Apollo 12 remembered
In 1991, as Apollo 12 Commander Pete Conrad reviewed the transcripts of his conversations relayed from the moon back to Earth, the significance of the only known microbial survivor of harsh interplanetary travel struck him as profound:
"I always thought the most significant thing that we ever found on the whole...Moon was that little bacteria who came back and lived and nobody ever said [anything] about it."
Although the space-faring microbe was described in a 1970 Newsweek article, along with features in Sky and Telescope and Aviation Week and Space Technology, the significance of a living organism surviving for nearly three years in the harsh lunar environment may only now be placed in perspective, after three decades of the biological revolution in understanding life and its favored conditions. As the lunar voyagers answered a similar question more than a century ago, in Jules Verne's classic, From the Earth to the Moon: "To those who maintain that the planets are not inhabited one may reply: You might be perfectly in the right, if you could only show that the earth is the best possible world."
The remarkable lunar survivor from Apollo 12 thus gives scientific pause. Three decades, the biological revolution
To a biologist, freeze-drying microbes for harsh space travel conjures up rather mundane kitchen science, a simple reenactment of how a yeast packet taken from the freezer can make bread dough rise prior to baking. But to a new breed of biologist exploring the harshest conditions on Earth, how a delicate microbe manages to counteract vacuum, boiling temperatures, burning radiation, and crushing pressures deep in the frozen icecaps is the study of life itself.
For example, only now after 30 years of biological progress can scientists begin to scan down the genetic script underlying the causes of malaria, syphilis, cholera and tuberculosis. Within a few years, it is estimated that 50 to 100 complete genomes of living organisms will be entirely deciphered, presenting the first opportunities for deep evolutionary comparisons and insights into exactly the remarkable means by which the common Strep. bacteria could revive itself after 2.6 years on the moon.
The Deep Sleep
The Surveyor probes were the first U.S. spacecraft to land safely on the Moon. In November, 1969, the Surveyor 3 spacecraft's microorganisms were recovered from inside its camera that was brought back to Earth under sterile conditions by the Apollo 12 crew.
The 50-100 organisms survived launch, space vacuum, 3 years of radiation exposure, deep-freeze at an average temperature of only 20 degrees above absolute zero, and no nutrient, water or energy source. (The United States landed 5 Surveyors on the Moon; Surveyor 3 was the only one of the Surveyors visited by any of the six Apollo landings. No other life forms were found in soil samples retrieved by the Apollo missions or by two Soviet unmanned sampling missions, although amino acids - not necessarily of biological origin - were found in soil retrieved by the Apollo astronauts.)
How this remarkable feat was accomplished only by Strep. bacteria remains speculative, but it does recall that even our present Earth does not always look as environmentally friendly as it might have 4 billion years ago when bacteria first appeared on this planet.
Extremophiles: Life on the Edge
When the first bacteria colonized the earth, there was no free oxygen to breathe and no ozone to block out the sun's damaging ultraviolet radiation. Oxygen was a poison gas. Nuclear radiation came from decaying uranium-235, which was about 50 times more abundant then than now. Appropriately referred to as the Hadean Eon (after the Greek underworld), the air was hot and full of noxious chemicals such as sulfurous gases released by volcanoes. However, there are bacteria which can live, even thrive, in a very wide variety of conditions that seem unfriendly to humans. Bacteria can survive unlikely changes of environment, including the growing list of space-hardiness conditions:
* Vacuum conditions, with bacteria taken down to near zero pressure and temperature, provided suitable care is exercised in the experimental conditions.
* Pressure, with viable bacteria after exposure to pressures as high as 10 tonnes per square centimeter (71 tons/sq-in). Colonies of anaerobic bacteria have recently been recovered from depths of 7 km (4.2 mi) or more in the Earth's crust.
* Heat. Bacteria survive after flash heating under dry conditions at temperatures up to 600 deg. C (1,112 deg. F). Archaebacteria that can withstand extreme heat have been found thriving in deep-sea hydrothermal vents and in oil reservoirs a mile underground
* Radiation, including viable bacteria recovered from the interior of an operating nuclear reactor. In comparison to space, each square meter on Earth is protected by about 10 tons of shielding atmosphere.
* Long preservation, including bacteria revived and cultured after some 25 million years of encapsulation in the guts of a resin-trapped bee. Microgravity Research and Astrobiology
NASA's mission is divided into five enterprises: Mission to Planet Earth, Aeronautics, Human Exploration and Development of Space, Space Science, and Space Technology. Marshall Space Flight Center is the designated lead center for microgravity research, under the Human Exploration and Development of Space (HEDS) enterprise in the 1998 NASA Strategic Plan. This directive answers two important scientific questions:
What is the fundamental role of gravity and cosmic radiation in vital biological, physical, and chemical systems in space, on other planetary bodies, and on Earth, and how do we apply this fundamental knowledge to the establishment of permanent human presence in space to improve life on Earth?
HEDS also plays an important role working with the other Enterprises to pursue answers to other fundamental questions, including: Does life exist elsewhere than on our planet?
While the concerns are real, the dangers suggested by some science fiction authors are completely speculative. Nonetheless, conservative sample return mission planning includes special handling and containment of extraterrestrial samples unless they are first shown to be harmless.
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The above story is based on materials provided by NASA/Marshall Space Flight Center--Space Sciences Laboratory.
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