CH A PTER ONE WHAT IS AN ALIEN he word alien is a popular word for an extra terrestrial life form or a being that originated beyond Earth No one knows if extraterrestrial life exists or ever existed but some scientists think that it is possible The branch of biology concerned with extra terrestrial life from microscopic organisms to intelligent beings is called exobiology or astrobiology Scientists in this field consider the conditions nec essary for life how it evolves how to detect alien life forms and the environments in
WHAT IS AN ALIEN which they might live whether in our own solar system or on any of the numerous planets orbiting other stars EXTRATERRESTRIAL LIFE The precise requirements for life are not known All liv ing things on Earth are based on the element carbon and need water for chemical reactions Hydrogen nitrogen phosphorous sulfur oxygen and other elements are also essential However if alien life forms exist they might be very different from any living thing on Earth Such life forms might be difficult to detect or even rec ognize as life At a basic level living things must be made of atoms that bond to form a variety of molecules at the tempera tures in their environment They probably require a liq uid water or perhaps ammonia hydrogen cyanide or liquid hydrocarbons for chemical reactions The envi ronment would have this liquid at or near the surface Life forms would also need sunlight or another energy source protection from ultraviolet radiation and proba bly an atmosphere Extraterrestrial intelligence is one step further than extraterrestrial life It means life from another world that is capable of thinking and working toward a Radio telescopes like this one in Virginia are capable of seeking out extraterrestrial signals from deep within outer space However nothing has been detected yet
INVESTIGATING UFOs AND ALIENS MOVE OVER LITTLE GREEN MEN Many people's concept of alien life is that of little green or gray beings with large heads and huge eyes These ideas Pulses of light for communication with other aliens Metallic surface for absorbing light Opening to scope chemicals from the atmosphere for growth and reproduction Lenses for detailed viewing of surroundings Orange underside for camouflage Body enlarges in sunlight AS Buoyancy sacks to maintain altitude deflate at lower altitude Just as Earth has life forms that have adapted to their differing environments in different ways alien life forms might have features that are better suited to different
WHAT IS AN ALIEN come from books and films and these aliens resemble life forms we know well people At least one scientist suggests that people are imagining extraterrestrial intelli gence all wrong Dr Maggie Aderin Pocock envisioned one way alien life could have adapted to a planet similar to Jupiter She hypothesized that silicon based aliens could look somewhat like floating jellyfish and survive on sunlight and chemicals They might not necessarily be intelligent enough to make contact with Earth though Aderin Pocock also reminds people that aliens on other worlds might have previously existed but became extinct before human life evolved purpose Work in the field of astrobiology has provided some evidence that evolution of other intelligent species in the Milky Way Galaxy is not impossible EXPLORATIONS Space exploration has been an important part of the search for extraterrestrial life Unmanned probes have visited every planet in the solar system plus many moons asteroids and comets Places in the solar system that seem most likely to 9
