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The Solar Systems in the Milky Way Galaxy

The Milky Way is the popular name for our own galaxy. It consists of an estimated 200 billion stars that we see as a milky cloud stretching across the night sky. Our own solar system seems to be on one of the radiating arms, about 26,000 light years from the center. Are other solar systems like ours, of a sun and several planets, in the Milky Way? Scientists are just beginning to get some answers.

A Challenge of Detection
- Orbiting planets can cause their closest stars to "wobble."
  
  Scientists have long searched for other solar systems in the Milky Way. Even though modern telescopes can detect stars and glowing clouds of gas vast distances away, planets have been difficult to find because they don't generate any light. Instead, they reflect a small portion of the light of their nearest star. "Dr. Marc" of NASA's "SpacePlace" compares finding their faint light to detecting, "a firefly next to a brilliant searchlight miles away."
  
  In the 1990s, astronomers discovered that planets could be detected by the slight gravitational pull they exerted on their closest stars. Instruments could measure tiny "star wobble" as a planet completed its orbit. In this way, by 2002, about 70 suspected solar systems were identified.
Breakthrough
- Kepler's ultra sensitive camera can detect the weak light reflected by planets.
  
  On March 6, 2009, NASA launched Kepler, an advanced space telescope designed to detect Earth type planets. NASA scientists have dubbed the Kepler Mission, "The Search for Habitable Planets." After analysis, the NASA team identified 700 likely candidates within the first 43 days of Kepler data.
  
  Then, on August 26, 2010, NASA announced the breakthrough. A solar system had been discovered, made up of two planets orbiting the same star--or "transiting" it in NASA terminology. The discovery of Kepler-9b and 9c, as the planets are called, after their star, Kepler-9, came after analyzing seven months of observations of 156,000 stars. It was, according to NASA, "the first confirmed planetary system with more than one planet...transiting the same star."
How They Did It
- As in this artist's imaginary rendering, Kepler found two planets orbiting the same star.
  
  The planets were found using the "ultra-precise" measurements of Kepler's camera. As each of the planets crosses the face of the star, the light radiating from it dips very slightly. By measuring timing and variation of these "dips", the NASA team was able to detect the masses and orbits of two distinct planets.
  
  In addition to the Kepler measurements, observations from ground stations such as the W.M. Keck Observatory in Hawaii were used to refine the findings. They show that both planets have about the same mass as Saturn, though Kepler-9b is the larger of the two. Kepler-9b is closer to the star, with an orbit of about 19 days. Kepler-9c has an orbit of about 38 days.

Astronomy