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A crowded universe

Monday - 1/23/2012, 9:18am  ET

planet500.jpg
Artist's impression of exoplanets, (Courtesy of NASA)

Greg Redfern, wtop.com

WASHINGTON - For many years, astronomers thought it to be a good possibility that planets other than those in our own solar system existed around other stars. The problem was that they needed proof to confirm the theory and exoplanet ponderings. It took the decades-long technological evolution of our instruments, telescopes, computers and eventually spacecraft for astronomers to get into the realm of exoplanets.

Astronomers find new planets orbiting other stars in several ways, but all of them have one thing in common: monitoring the parent star's light and/or orbit to detect absolutely minuscule changes in either of these. This is where the telescopes and the instruments have had to evolve in order to obtain, discover and process these changes into a new planet discovery.

Astronomers are finding new exoplanet candidates almost daily using earth-bound telescopes and NASA's planet hunting Kepler spacecraft. Kepler has found 35 confirmed exoplanets, including exoplanets the size of Earth, smaller than Earth, larger than Jupiter, orbiting red dwarf stars and double star systems. Kepler, at last count, has over 2,300 exoplanet candidates and this number keeps growing. Scientists have yet to directly image one of these exoplanets, but can learn their size, mass and probable environmental conditions based on their orbit and the type of star they orbit.

Astronomers have developed the concept of "the habitable zone," the orbital area around a star that would allow liquid water to exist. If a star is big and bright and hot, or small, dim and cool, the habitable zone will vary accordingly. In our own solar system, we see the habitable zone only exists on Earth, as Mercury and Venus are too close to the sun, while Mars and beyond are too far out. We know water exists elsewhere in the solar system, but it is liquid on the surface of Earth only.

Very recently, there was a news announcement that got very little, if any, exposure in the media, but had major implications as to exoplanets and the very nature of our Milky Way galaxy. A team of astronomers monitoring the night sky for eight years to capture "microlensing events" announced that based on their findings, they calculated that at least one planet orbits every star in our Milky Way galaxy. That, dear reader, equates to at least 100 billion planets in our galaxy.

As explained in this news release, "The team's conclusions are gleaned from a planet search technique called microlensing. The technique takes advantage of the random motions of stars, which are generally too small to be noticed. If one star passes precisely in front of another star, the gravity of the foreground star bends the light from the background star."

"This means that the foreground star acts like a giant lens amplifying the light from the background star. A planetary companion around the foreground star can produce additional brightening of the background star. This additional brightening reveals the planet, which is otherwise too faint to be seen by telescopes."

"The higher the mass of the "lensing" star, the longer is the duration of the microlensing event. Typical microlensing events due to a star last about a month. But the extra brightening due to a planet typically lasts a few hours to a couple of days."

"Using the microlensing technique, astronomers can determine a planet's mass. This method, however, does not reveal any clues about the world's composition." For our galactic neighborhood, their study reports that within a mere 50 light years of Earth there are at least 1,500 planets. And, most of the planets in our galaxy should be smaller, Earth sized worlds instead of the larger Jupiter and Saturn variety.

What the study did not say -- because there is no proof -- but what can be said, is that what goes on in our galaxy must be going on in other galaxies. In other words, other galaxies must have the same ratio of at least one planet to every star. I say this because our galaxy is not unique, but is just one in billions upon billions of galaxies observed in the universe. The smallest galaxies are measured in terms of millions of stars while the largest have a trillion or more stars.

The sheer number of galaxies, their stars, and now their planets, is truly staggering. It is inconceivable that with such mind-numbing numbers present, life other than our planet has to exist. And let me add "intelligent, sentient life forms" to that last presumption. With such an incredible array of life on our own planet there will be planets in the habitable zone of their parent star that will have the time and the conditions for life forms to develop.

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