According to a new study, 92% of Earth-like planets (those most likely to contain alien life) haven't been born yet.
Researchers Peter Behroozi and Molly S. Peeples used data from the Hubble telescope and the Kepler space observatory to conduct the theoretical study, which appears this week in the Monthly Notices of the Royal Astronomical Society.
Behroozi said in a statement that they undertook the research to figure out "the Earth's place in the context of the rest of the universe," concluding that "compared to all the planets that will ever form in the universe, the Earth is actually quite early."
Our solar system, NASA explains, was formed 4.6 billion years ago. Our planet is about 4.54 billion years old, and our sun will burn out in 6 billion years. The scientists' projections show that from the time our solar system started until now, roughly 8% of all Earth-like (or habitable planets) that will ever exist in the universe have been formed. That's because there's a lot more of the gas needed to make planets now than there was billions of years ago. Per NASA:
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.
In other words, the study suggests that if alien life exists it will be in the future. Behroozi and Peeples put it this way in their paper's abstract (emphasis mine):
However, if existing gas within virialized dark matter haloes continues to collapse and form stars and planets, the Universe will form over 10 times more planets than currently exist. We show that this would imply at least a 92 per cent chance that we are not the only civilization the Universe will ever have.
But they add that it's likely the bulk of new Earth-like planets will be born in galaxies outside of our Milky Way—which means that even if our descendants are able to somehow spot alien life, they likely won't be able to reach them. But we'll keep our fingers crossed.
Danielle Wiener-Bronner is a news reporter.