With NASA's Kepler mission still turning up cosmic wonders, and a slew of exoplanet-hunting scopes on deck, the chance of finding a second Earth has never seemed higher. And yet, time may be against us when it comes to meeting our squishy galactic brethren: according to a new theoretical study, 92% of Earth-like worlds haven't been born yet.
Using data collected by the Hubble Space Telescope and the Kepler mission, a team of astronomers at NASA's Space Telescope Science Institute has, for the first time, estimated when Earth-like worlds (small, rocky planets in the not-too-hot, not-too-cold habitable zone of their star) are likely to appear on the scene throughout the lifespan of the Universe. Apparently, this Blue Marble is early to the party.
When our solar system was born 4.6 billion years ago, only 8% of Earth-like planets existed. When our Sun winks out a couple eons down the road, many future Earths will have yet to coalesce.
How did the astronomers arrive at these conclusions? Basically, by staring off into really faraway space. Looking at distant galaxies is like peering back in time, and by collecting snapshots of the early Universe, we can reconstruct all sorts of interesting things, including rates of star formation.
Turns out, while galaxies were churning out stars very rapidly in the aftermath of the Big Bang, this early burst of productivity only used up a small fraction of the Universe's hydrogen and helium, the elements needed to create more complex forms of matter. The cosmic fuel tank is still nearly full, so to speak. That means new stars -- and new rocky plants -- will continue to form far into the future. In fact, the researchers estimate that most of the remaining 92% of planets will emerge between 100 billion years and 1 trillion years from now. We are the cosmic forerunner.
Of course, this doesn't mean we should all stick ourselves in a cryobank and time travel to a less lonely future. Thanks to the Kepler mission, astronomers now estimate that today, there are a billion Earth-like worlds in our galaxy alone. If we're lucky, one of them contains some slimy alien microbes, or at least an atmosphere we can terraform. Who knows, maybe there's even a giant alien megastructure or two somewhere winking at us from across the light years.
Still, I can't help but image that billions of years from now, archaeologists will convene to discuss the strange fragments of space junk found in the vicinity of the Sol system, and wonder who those ancient people were.
Top: Artist's depiction of a potentially habitable world orbiting the Sun-like star Gliese 581g. Image Credit: L. Calçada, ESO