The search for extraterrestrial life has been an inherent NASA mission since the earliest days of the space agency, although not part of its founding charter.

Searching for water-related evidence for life 220 million mi. from Earth, the Mars rover Opportunity images the tracks it used to drive into and out of the half-mile-wide Victoria crater.Credit: NASA/JPL/SPACE SCIENCES INSTITUTE

Now, 50 years after NASA's inception, the quest to find life beyond Earth has been elevated to one of the key justifications for the agency's existence.

This goal is increasingly the focal point for international cooperation. But as European, Japanese and especially Chinese space capabilities mature, new competition could arise.

The hunt is also spawning billions of dollars in robotic sensor and spacecraft development around the world. It's still true that "somewhere, something incredible is waiting to be known," as the late astronomer Carl Sagan said.

Now every day, scientists and engineers go to jobs - many at small, new high-tech companies - aimed at developing cutting-edge science and technology specifically geared toward finding evidence of alien life on other planets.

Aside from debate over demons and gods dreamed up by pre-historic cultures, the more serious question about the possibility of life in the cosmos was discussed at a scholarly level as far back as ancient Greece. And that was 2,000 years before Polish astronomer Copernicus found that the Earth and planets orbit the Sun.

The existence of billions of other galaxies with an infinite number of similar suns and planets was not even known until 1923. That's when Edwin Hubble used the then-new observatory at Mt. Wilson, Calif., that towers high above the Jet Propulsion Laboratory, which is now critical to many space missions.

But not until the creation of NASA could the search for life beyond Earth be placed into the arena where it could finally be tested empirically, according to NASA historian Steven J. Dick.

"From the early 1960s onward, NASA funded laboratory experiments on the origin of life, revived planetary science, sponsored theoretical and observational studies on planetary systems, and assembled the flagship program in the Search for Extraterrestrial Intelligence (SETI). These were all elements of the budding discipline that became exobiology,'" says Dick in a 50th anniversary-related study of the topic. Now exobiology has evolved into the broader discipline of "astrobiology" - a formal new branch that investigates the existence of living organisms on planets other than Earth.

"Astrobiology has a compelling driving force . . . to place Homo sapiens in a cosmic context' just as Charles Darwin placed them in a terrestrial context," says Dick.