Astrobiology is the study of the origin, evolution, distribution, and future of extraterrestrial life. This interdisciplinary field takes up the search for habitable environments in our Solar System and habitable planets outside our Solar System, the search for evidence of prebiotic chemistry, laboratory and field research into the origins and early evolution of life on Earth, and studies of the potential for life to adapt to challenges on Earth and in outer space. Astrobiology addresses the question of whether life exists beyond Earth, and how humans can detect it if it does.
Astrobiology makes use of physics, chemistry, astronomy, biology, molecular biology, ecology, planetary science, geography, and geology to investigate the possibility of life on other worlds and help recognize biospheres that might be different from the biosphere on Earth. Astrobiology concerns itself with interpretation of existing scientific data; given more detailed and reliable data from other parts of the universe, the roots of astrobiology itself—physics, chemistry and biology—may have their theoretical bases challenged. Although speculation is entertained to give context, astrobiology concerns itself primarily with hypotheses that fit firmly into existing scientific theories.
In planetary astronomy
, the Rare Earth hypothesis
argues that the emergence
of complex multicellular life
) on Earth
required an improbable combination of astrophysical
events and circumstances. The term "Rare Earth" comes from Rare Earth: Why Complex Life Is Uncommon in the Universe
(2000), a book by Peter Ward
, a geologist and paleontologist, and Donald E. Brownlee
, an astronomer and astrobiologist
The rare earth hypothesis is the contrary of the widely accepted principle of mediocrity (also called the Copernican principle), advocated by Carl Sagan and Frank Drake, among others. The principle of mediocrity concludes that the Earth is a typical rocky planet in a typical planetary system, located in a non-exceptional region of a common barred-spiral galaxy. Hence it is probable that the universe teems with complex life. Ward and Brownlee argue to the contrary: planets, planetary systems, and galactic regions that are as friendly to complex life as are the Earth, the solar system, and our region of the Milky Way are very rare.
By concluding that complex life is uncommon, the Rare Earth hypothesis is a possible solution to the Fermi paradox: "If extraterrestrial aliens are common, why aren't they obvious?"
Frank Donald Drake PhD
is an American astronomer
. He is most notable as one of the pioneers in the search for extraterrestrial intelligence, including the founding of SETI
, mounting the first observational attempts at detecting extraterrestrial communications in 1960 in Project Ozma
, developing the Drake equation
, and as the creator of the Arecibo Message,
a digital encoding of an astronomical and biological description of the Earth and its lifeforms for transmission into the cosmos.