On October 30, NASA decided to retire its first revolutionary planet-hunting spacecraft, the Kepler Space Telescope, after it ran out of fuel. During its mission of nine years, much longer than the 3.5 years it had been planned for, Kepler observed 5,30,506 stars and discovered 2,662 exoplanets (planets outside the solar system), many of which are potential places for life.
“When we started conceiving this mission 35 years ago, we didn’t know of a single planet outside our solar system,” said the Kepler mission’s founding principal investigator, William Borucki, now retired from NASA. “Now we know planets are everywhere.”
A recent analysis of data from Kepler indicates that 20-50 per cent of the stars visible in the night sky are likely to have small, possibly rocky, planets, similar in size to the earth and located within the habitable zone of their parent stars. Its discoveries have also shown that there are many planetary systems with such a high density of planets that the solar system looks sparse in comparison.
Named after the astronomer Johannes Kepler, the spacecraft was launched on March 6, 2009. It was originally positioned to stare continuously at 1,50,000 stars in one star-studded patch of the sky in the constellation Cygnus. Kepler used the “transit method”—observing the star’s dipping light as a planet transits in front—to discover exoplanets.
Four yea rs into the mission, after the primary mission objectives had been met, mechanical failures temporarily halted observations. The mission team was able to devise a fix, switching the spacecraft’s field of view roughly every three months. This enabled an extended mission for the spacecraft, renamed K2, which lasted as long as the first mission and increased the number of surveyed stars up to more than 5,00,000.
Before Kepler was retired, it was driven to its full potential. The enormous amount of data from Kepler is expected to serve the astronomical community a decade or more in its search for new planets.
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