Planets: Where Are Our Many Fellow Blue-Green Planets?

Maybe--just maybe--the reason we don't see masses of other life-filled, maybe even blue-green, planets is because the great majority (92 percent) of those don't yet exist, a theoretical study recently noted. The work was based on analysis of data collected by Kepler space observatory and NASA's Hubble Space Telescope.

Study author Peter Behroozi, of the Space Telescope Science Institute (STScI) in Baltimore, said in a release, "Compared to all the planets that will ever form in the universe, the Earth is actually quite early."

The collected material from Hubble shows the star formation history of the universe. From this, the scientists noted that while the universe produced stars at a speedy rate 10 million years ago, only a small proportion of the universe's total hydrogen and helium gas was used. These days, star birth occurs at a slower rate, but the universe has a large reserve of leftover gas and will be able to produce planets and stars far into the future, the release noted.

"There is enough remaining material [after the big bang] to produce even more planets in the future, in the Milky Way and beyond," co-investigator Molly Peeples of STScI said in the release.

From the Kepler data, the researchers found that there ought to be 1 billion worlds the size of Earth in the Milky Way galaxy right now, many of them likely rocky. Also, considering the 100 billion other galaxies in the universe means many other Earth-like planets could show up in the future, according to the release.

The study results were published recently in Monthly Notices of the Royal Astronomical Society. 

More information about the Hubble Space Telescope is here.

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