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What is Astrobiology?
As defined in the NASA Strategic Plan, Astrobiology is the study of the living universe, providing a scientific foundation for the multidisciplinary investigation of the origin and distribution of life, including the role of physical forces, planetary atmospheres, and ecosystem interactions in the evolution of living systems.
What We Know about the Living Universe
- We have analyzed complex organic chemistry in interstellar clouds and have discovered more planets outside our solar system than in it.
- Life's habitable zone has expanded beyond the boiling point of water, below freezing, at extreme acid and base conditions, 4 km below the land surface, over 6 km below sea level, under extreme radiation conditions, for years unprotected in space. In addition, microbial life can remain dormant but viable for millions of years.
- Liquid water once flowed on the surface of Mars and may exist below its surface under conditions that some terrestrial organisms would find habitable.
- Liquid water probably exists today below the icy crust of Jupiter's moon Europa.
- Life on Earth has been traced back 3.8 billion years to the end of the heavy planetesimal bombardment period.
- We see both the fragility and robustness of life, as we investigate the history of environmental change and mass extinctions -- and compare it to the changes seen on Mars.
- Life from Earth survives in space, but experiences complex physiological and chemical changes induced by the space environment.
- Comets and asteroids strongly influence planetary evolution. Their effects range from bringing life-giving water and organics to developing worlds to periodically bombarding the life upon them to extinction.
- Natural processes such as comet and asteroid impacts can cause the transfer of material from one world to another sufficiently quickly and with sufficient gentleness to preserve the microbial life within it (if any).
- Humanity may be entering a new evolutionary territory -- space -- in a manner analogous to the first sea creature crawling out onto the land. This time, however, the environment and perhaps even some of the organisms can be engineered for evolutionary success. As a result, no biological or technological barrier to directed or undirected evolution beyond Earth has been identified to date.
The "habitable zone"
for terrestrial life is much broader than previously thought. Examples
of life at extreme
conditions include:
Hottest: 113°C--Pyrococcus furiosus (Vulcano Island, Italy)
Coldest: -15°C--Crypotendolithotrophs (Antarctica)
Deepest: 2 miles (land)--bacteria found in rocks underground
Most acidic: pH 0.0--unclassified organisms growing on gypsum in caves
Most basic: pH 11--Alkaliphilic bacteria
Highest radiation: 5 Mrads--Deinococcus radiodurans (ubiquitous)
Longest period in space: 6 years--Bacillus subtilis (Long Duration Exposure Facility)
Farthest: Moon--Humans, Streptococcus mitus from Surveyor III camera after 3 years unprotected on lunar surface
Longest dormancy: 20-40 million years--Bacillus revived from gut of bee in 20-40-million-year-old Dominican amber
Deepest and Highest pressure: 1200 atm--cold seep community at bottom of Marianas Trench
Saltiest: 30%--halophilic bacteria