Earth is an oddity, arriving early in the evolving Universe, a new theoretical study suggests.
Based on an assessment of data collected by NASA’s Hubble Space Telescope and the prolific planet-hunting Kepler space observatory, the study suggests that when our solar system was born 4.6 billion years ago only 8% of the potentially habitable planets that will ever form in the universe existed.
That means 92% are yet to form.
“Our main motivation was understanding the Earth’s place in the context of the rest of the universe,” said study author Peter Behroozi of the Space Telescope Science Institute (STScI) in Baltimore.
“Compared to all the planets that will ever form in the universe, the Earth is actually quite early.”
Looking far away and far back in time, Hubble has given astronomers a “family album” of galaxy observations that chronicle the universe’s star formation history as galaxies grew. The data show that the Universe was making stars at a fast rate 10 billion years ago, but the fraction of the Universe’s hydrogen and helium gas that was involved was very low. Today, star birth is happening at a much slower rate than long ago, but there is so much leftover gas available that the universe will keep cooking up stars and planets for a very long time to come.
“There is enough remaining material after the Big Bang to produce even more planets in the future, in the Milky Way and beyond,” said co-investigator Molly Peeples of STScI.
Kepler’s planet survey indicates that Earth-sized planets in a star’s habitable zone, the perfect distance that could allow water to pool on the surface, are ubiquitous in our galaxy. Based on the survey, scientists predict that there should be 1 billion Earth-sized worlds in the Milky Way galaxy at present, a good portion of them presumed to be rocky. That estimate skyrockets when you include the other 100 billion galaxies in the observable Universe.
The results will appear in the Monthly Notices of the Royal Astronomical Society.