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Study finds billions of Earth-like sites

WASHINGTON — Space is vast, but it may not be so lonely after all: A study finds the Milky Way is teeming with billions of planets that are about the size of Earth, are orbiting stars like our sun, and are not too hot and not too cold for life.

Astronomers using NASA data have calculated for the first time that in our galaxy alone, there are at least 8.8 billion stars with Earth-size planets in the habitable temperature zone.

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The study was published Monday in the journal Proceedings of the National Academy of Science.

For perspective, the study found more Earth-like planets than there are people on Earth.

As for what it says about the odds that there is life somewhere out there, it means ‘‘just in our Milky Way galaxy alone, that’s 8.8 billion throws of the biological dice,’’ said study coauthor Geoff Marcy, a longtime planet hunter from the University of California at Berkeley.

The next step, scientists say, is to look for atmospheres on these planets with powerful space telescopes that have yet to be launched. That would yield further clues to whether any of these planets do harbor life.

The findings also raise a blaring question, Marcy said: If we aren’t alone, why is ‘‘there a deafening silence in our Milky Way galaxy from advanced civilizations?’’

In the Milky Way, about 1 in 5 stars that are like our sun in size, color, and age have planets that are roughly Earth’s size and are in the habitable zone where life-crucial water can be liquid, according to intricate calculations based on four years of observations from NASA’s now-crippled Kepler telescope.

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