There may be more Earth-like planets than grains of sand on all our beaches

New research contends that the Milky Way alone is flush with billions of potentially habitable planets -- and that's just one sliver of the universe.

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Eric Mack
3 min read

The potential number of Earth-like planets has suddenly exploded. Niels Bohr Institute / University of Copenhagen

The fascinating question of whether we are alone in the universe basically comes down to some intricate mathematical calculations.

A new study combines exoplanet data from the Kepler Space Telescope with a new version of a 250-year-old method for determining orbital periods and positions of planets. The research calculates that in our galaxy alone, there could be billions of planets hosting liquid water, habitable conditions and perhaps even life.

"We decided to use this method to calculate the potential planetary positions in 151 planetary systems, where the Kepler satellite had found between three and six planets...But we only made calculations for planets where there is a good chance that you can see them with the Kepler satellite," Steffen Kjær Jacobsen, co-author of the study published in the Monthly Notices of the Royal Astronomical Society journal, said Wednesday in a statement.

The team predicted a total of 228 planets in the 151 planetary systems and then made a priority list with 77 planets in 40 planetary systems that are likely the easiest to observe with Kepler.

"We have encouraged other researchers to look for these. If they are found, it is an indication that the theory stands up," said Jacobsen, a graduate student at the Niels Bohr Institute at the University of Copenhagen.

Digging deeper into the data, the researchers looked at how many planets were likely to be in the habitable zone where conditions to support liquid water and life might exist. They found an average of one to three planets in the habitable zone in each planetary system. Extrapolate those calculations further, and you arrive at the conclusion that if the math holds, there may be billions of habitable planets in the Milky Way, which is itself just one of billions of galaxies.

The 7 confirmed exoplanets most likely to host life (pictures)

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Should these calculations hold up -- and the researchers behind them encourage astronomers to check to see whether the planets they predict are actually there to help bolster their case -- it means that the chances of our planet being the universe's only potentially habitable rock that actually hosts life would be not one in a million, one in a billion or even one in a trillion -- but one in a sextillion. (In case this is your first time seeing that word, a sextillion is a one with 21 zeroes behind it.)

Actually, if the estimates of 40 billion Earth-sized planets in habitable zones of sun-like or red dwarf stars in the Milky Way and the estimate of the 100 billion to 200 billion galaxies in the universe are accurate -- and if the average galaxy has roughly the same number of Earth cousins as the Milky Way, then the chances that we are the only planet with life are more like one in 6 sextillion.

To offer a frame of reference for that number, consider the amount of sand on Earth's beaches.

Jason Marshall, aka "The Math Dude," has calculated that there are roughly 5 sextillion grains of sand on all our planet's beaches combined. So take every grain of sand on every beach on Earth and you can begin to be able to actually visualize how many planets we're talking about. Then you begin to wonder why we aren't overrun with aliens.

The apparent absence of aliens (depending who you ask) then is probably due to the whole problem of figuring out interstellar travel. To really understand the universe, you have to imagine a single beach containing all the sand from all our beaches, but then add the wrinkle that each grain of sand is separated from its nearest neighbor grain of sand on this beach by at least several trillions of miles.

While that's not a distance we can really comprehend, at least it's a number we've heard of. Maybe all this cosmic math isn't so boring after all. It's significant in its ability to quantify our comparative insignificance.