The Milky Way galaxy is so big, that there's no doubt, statistically speaking, that ETs exist.

That's what several prominent scientists say on the month-long series "Are We Alone?," airing on the Science Channel.

But what do these otherworldly denizens look like? Are they smart or dumb? Will we ever come face to face with them?

On the first installment of "Aliens: The Definitive Guide," premiering tonight, famed theoretical physicist Michio Kaku is among those who take a strong stand on the biggest questions about the search for intelligent life in the universe.

"Some scientists say that perhaps we are the only life forms in the universe. Give me a break! I mean, how many stars are there out there in the universe, anyway? The Hubble Space Telescope can see about a hundred billion galaxies -- that's the visible universe," Kaku says on the alien TV special.

"Each galaxy consists of a hundred billion stars. Do the math. A hundred billion times a hundred billion is 10 sextillion. That's one with 22 zeros after it. There definitely are aliens in outer space -- they're out there!"

Recent planetary discoveries by NASA's Kepler Space Telescope confirm the existence of huge numbers of planets in our nearby galactic neighborhood, and the number of Earth-like worlds is on the increase, raising expectations that life has evolved on many of them.

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"There's an exotic zoo of planets out there. Many of them aren't anything like the kind of planets we find in our own solar system," according to astrobiologist Lewis Dartnell. "One kind of planet common in the galaxy is a water world -- a planet with a very deep ocean, perhaps hundreds of kilometers deep. The life in these water worlds might look pretty recognizable."

But while scientists still don't know exactly what life may look like on worlds hundreds of trillions of miles away (see illustration above), Dartnell theorizes about possible similarities found between Earth and conditions that may have developed on another planet.

"The propulsion mechanisms that are adapted and evolved by alien fish would be pretty similar to the propulsion mechanisms that you find on Earth simply because they're solving the same survival situation with the means available to them."

Because of the advances in our ability to locate other planets in the Milky Way galaxy, scientists now estimate there could be hundreds of billions of planets that may harbor life. But how intelligent might that life be?

"There are three basic ingredients to become an advanced civilization," says Kaku, one of the leading physicists in the world.

"First, you have to have stereo eyes -- eyes of a hunter -- because predators are smarter than prey. That's why we say 'sly fox' and 'dumb as a bunny.' If you are a predator, that means you have to have camouflage and stealth. You have to be able to outsmart the prey.

"Second, you have to have an opposable thumb, a hand, a claw, a tentacle -- something by which you can manipulate the environment to create machines and, eventually, starships.

"And third, language. You have to be able to accumulate knowledge between generations. The knowledge you get from this generation has to be handed down in order to create vast civilizations capable of taking you to the stars."

"Aliens: The Definitive Guide" premieres tonight on the Science Channel. Check your local listings for channel and time.

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  • NASA's Kepler Mission Discovers Planet

    In this handout illustration made available on December 5, 2011 by NASA, the Kepler-22b, a planet known to comfortably circle in the habitable zone of a sun-like star is digitally illustrated. For the first time NASA's Kepler mission has confirmed a planet to orbit in a star's habitable zone; the region around a star, where liquid water, a requirement for life on Earth, could persist. The planet is 2.4 times the size of Earth, making it the smallest yet found to orbit in the middle of the habit. Clouds could exist in this earth's atmosphere, as the artist's interpretive illustration depicts. (Photo Illustration by Ames/JPL-Caltech/NASA via Getty Images)

  • NASA's Kepler Mission Discovers Planet

    In this handout illustration made available on December 5, 2011 by NASA, a diagram compares our own solar system to Kepler-22, a star system containing the first 'habitable zone' planet discovered by NASA's Kepler mission. The habitable zone is the sweet spot around a star where temperatures are right for water to exist in its liquid form. Liquid water is essential for life on Earth. The diagram displays an artist's rendering of the planet comfortably orbiting within the habitable zone, similar to where Earth circles the sun. Kepler-22b has a yearly orbit of 289 days. The planet is the smallest known to orbit in the middle of the habitable zone of a sun-like star and is about 2.4 times the size of Earth. (Photo Illustration by Ames/JPL-Caltech/NASA via Getty Images)

  • Extrasolar Planet HD 209458 b, Osiris

    Artist's conception released by NASA of extrasolar planet HD 209458 b, also known as Osiris, orbiting its star in the constellation Pegasus, some 150 light years from Earth's solar system. Scientists have used an infrared spectrum -- the first ever obtained for an extrasolar planet -- to analyze Osiris' atmosphere, which is said to contain dust but no water. The planet's surface temperature is more than 700 Celsius (1330 Fahrenheit).'

  • Planet & Its Parent Star

    Picture released 04 October 2006 by the European Space Agency shows an artist's impression of a Jupiter-sized planet passing in front of its parent star. Such events are called transits. When the planet transits the star, the star's apparent brightness drops by a few percent for a short period. Through this technique, astronomers can use the Hubble Space Telescope to search for planets across the galaxy by measuring periodic changes in a star's luminosity. The first class of exoplanets found by this technique are the so-called 'hot Jupiters,' which are so close to their stars they complete an orbit within days, or even hours. A seam of stars at the centre of the Milky Way has shown astronomers that an entirely new class of planets closely orbiting distant suns is waiting to be explored, according to a paper published 04 October 2006. An international team of astronomers, using a camera aboard NASA's Hubble telescope, delved into a zone of the Milky Way known as the 'galactic bulge', thus called because it is rich in stars and in the gas and dust which go to make up stars and planets. The finding opens up a new area of investigation for space scientists probing extrasolar planets - planets that orbit stars other than our own. AFP PHOTO NASA/ESA/K. SAHU (STScI) AND THE SWEEPS SCIENCE TEAM

  • Hot Jupiter

    Picture released 04 October 2006 by the European Space Agency shows an artist's impression of a unique type of exoplanet discovered with the Hubble Space Telescope. This image presents a purely speculative view of what such a 'hot Jupiter' (word dedicated to planets so close to their stars with such short orbital periods) might look like. A seam of stars at the centre of the Milky Way has shown astronomers that an entirely new class of planets closely orbiting distant suns is waiting to be explored, according to a paper published 04 October 2006. An international team of astronomers, using a camera aboard NASA's Hubble telescope, delved into a zone of the Milky Way known as the 'galactic bulge', thus called because it is rich in stars and in the gas and dust which go to make up stars and planets. The finding opens up a new area of investigation for space scientists probing extrasolar planets - planets that orbit stars other than our own. AFP PHOTO NASA/ESA/K. SAHU (STScI) AND THE SWEEPS SCIENCE TEAM

  • The Goldilocks Planet: Glises 581 G

    Scientist have found a new potentially habitable planet.

  • Imagining Extrasolar Planets

    From the Spitzer Science Center. While astronomers have identified over 500 planets around other stars, they're all too small and distant to fill even a single pixel in our most powerful telescopes. That's why science must rely on art to help us imagine these strange new worlds. From Spitzer Space Telescope. Even without pictures of these exoplanets, astronomers have learned many things that can be illustrated in artwork. For instance, measurements of the temperatures of many "Hot Jupiters," massive worlds orbiting very close to their stars, hint that their atmospheres may be as dark as soot, glowing only from their own heat. While "Hot Jupiters" would be relatively dark in visible light, compared to their stars, their brightness is proportionally much greater in the infrared. Illustrating this dramatic contrast change helps explain why the infrared eye of NASA's Spitzer Space Telescope plays a key role in studying exoplanets. As our understanding evolves, so must the artwork. Astronomers found a blazing hot spot on the exoplanet Upsilon Andromedae b that at first, appeared to face towards its star. More data has revealed that the hottest area is actually strangely rotated almost 90 degrees away, near the day/night terminator. WASP 12b is as hot as the filament in a light bulb, and would be blazing bright to our eyes. Most interestingly, if it proves to have a strongly elliptical orbit, as first thought, calculations show it would be shedding some of its outer atmosphere <b>...</b>