There are no glowing fingers or Reese's Pieces in National Geographic's alien-filled 'Extraterrestrial,' but the message is clear: Earth is not that special when it comes to developing life.

The television special highlights two very different worlds from Earth, both teeming with life that astronomers believe could evolve if given the right set of conditions. Using computer models and armed with basic evolutionary theory, the scientists imagined not only what conditions might exist on their theoretical planets, but also how life may interact with the environment to form a thriving ecosystem.

"I've seen a lot of aliens on the silver screen and [television] screen that, while they may serve to be entertaining, are not very plausible," said Seth Shostak, senior astronomer for the SETI Institute scanning the skies for signs of intelligent life, in an interview. "Here was a plan to make aliens that make sense."

It was that concept that drew Shostak, a SPACE.com contributor, to appear in the two-hour program which airs May 30 (National Geographic, 9:00 - 11:00 p.m. ET/PT).

More than 130 extrasolar planets have been found by astronomers, many extremely massive and too close to their star parents to support life. The grand prize of planet hunters is the Earth-size planet in a comfortable orbit around its star.

The proposed Terrestrial Planet Finder, a two-telescope NASA project slated launch around 2014, could one day find those planets and peek into their atmosphere composition. But other space and ground-based telescopes will also join the hunt, including the Earth-size planet seeker Kepler slated for a 2008 launch and the Space Interferometry Mission to begin in 2011. Europe's Darwin and Eddington missions will also hunt for other planets from space, while astronomers continue to seek them out from terra firma.

Both of the planets visited in 'Extraterrestrial' are within about 50 light-years of Earth.

Aurelia, an Earth-sized planet tidally locked with its stellar parent, presents one fixed face toward a warm red dwarf and it is there - not the perpetually frozen waste that never sees sunlight - that life thrives. Meanwhile, Blue Moon, which orbits an enormous gas giant that is itself orbiting a binary star system, is covered in life-giving water and an atmosphere so dense that enormous winged Skywhales can take flight.

Gems such as the sheer oddity of Blue Moon's orbital geometry, or the hazards of Aurelian life due to constant bombardment from powerful solar flares thought to be a red dwarf star's signature, draw the attention but are too few in the beginning.

While slow to start, 'Extraterrestrial' presents an intriguing, if somewhat conventional, view of how life might evolve on an extrasolar planet. The researchers admit as much by focusing on water-bearing worlds and carbon-based life systems.

"It's conservative, in a sense, to focus on carbon-based life," Shostak said, but added that water may always be a good indicator of habitable planets. "NASA's mantra is follow the water, and I think that was sort of our mantra too."

NASA's Mars rovers Spirit and Opportunity, for example, were sent to two specific areas on the red planet to hunt for signs of water. Opportunity found evidence that its Meridiani Planum landing site was once drenched in water, while Spirit found signs this week pointing to a wet and violent past at Gusev Crater.

Unlike the Discovery Channel's 'Alien Planet,' which used the alien artwork of Wayne Barlowe to demonstrate the mechanics of how smart robotic probes might explore a distant world, 'Extraterrestrial' extrapolates otherworldly animals and plants using analogues found on Earth.

Eyes, for example, have evolved several times on Earth and are likely to pop up on other light-filled worlds, researchers said. Other sensory organs will likely always be near the brain for better information processing and even the appearance of 'Extraterrestrial' creatures, including an emu-like, two legged Aurelian beast dubbed a Gulphog, are based on rules fauna follow on Earth.

"That Gulphog looks like some cross between an ostrich and a dinosaur," Shostak said. "But these shapes are not completely random and [on Earth] nature has happened upon them over and over."

No matter what the form it takes, odds are humans will at least take more than a passing interest should alien life prove a reality.

A National Geographic-commissioned telephone survey of 1,000 Americans found that 60 percent believe life exists on other worlds. About 90 percent of those who believe in extraterrestrial life thought the Earth should respond to any communications emanating from an alien planet.

Just be sure to have your Reese's Pieces handy when they come calling.

National Geographic's 'Extraterrestrial' will appear on the National Geographic Channel from 9:00-11:00 p.m. ET/PT. (Check local listings).