Astronomers have recently acknowledged what many scientists have long considered a possibility; that the Milky Way galaxy is home to billions of Earth-like planets.

And if only one of them has life developed on its surface, it would answer one of the longest-standing questions in human history; Are we alone in the universe?

The revelation may not come as such a big surprise to many. After all, the universe is a really big place. In fact, it is so freakishly large that despite our very best calculations and theories, we’ve not been able to fully understand its true size.

Nonetheless, astronomers assume that the proper distance—the distance as would be measured at a specific time, including the present—between our planet and what is considered the edge of the observable universe is 46 billion light-years (14 billion parsecs), which means that the diameter of the observable universe about 93 billion light-years (28 billion parsecs).

But compared to the size of the universe, the Milky Way is really small. It is estimated that our galaxy is home to around 400 Billion stars, although that number has been the subject for debate for years.

If that’s the case and there are 400 billion stars in the Milky Way, and each star had exactly one planet orbiting it, then it would mean there are 400 billion planets–exoplanets–out there.

The Milky way, on the other hand, is part of a massive intergalactic structure estimated to be around 500 million light-years across and is believed to be home to around 100,000,000,000,000,000 Suns extended through its 100,000 150,000 galaxies, called Laniakea.

Data from NASA’s planet-hunting telescope

To understand our place in the galaxy, we’ve relied on data gathered by NASA’s planet-hunting Kepler telescope. And after revising the data Kepler has gathered throughout the years, astronomers have estimated that our galaxy may very well be littered with warm, watery planets that are very similar to Earth.

According to scientists at Penn State University who combed through data from Kepler, the galaxy we live in might be a sweet spot for Earth-like planets.

According to the results of their research published in The Astronomical Journal, there are Earth-like planets orbiting one in every four sun-like stars.

Doing the Math it means there could be around 10 billion Earth-like planets in our galaxy alone.

This is a huge number in our efforts to find life on other planets. If there are exoplanets out there that are similar to Earth; have liquid water on their surface, an atmosphere that protects the surface from harmful cosmic radiation, and the surface temperature is just right, then we could have a lot of planets with similar characteristics to Earth that may be candidates for life.

This data is crucial for the Wide-Field Infrared Survey Telescope, which is expected to launch into space in the mid-2020s. The Wide-Field Infrared Survey Telescope will explore the galaxy hunting for signs of oxygen and water vapor in distant planets orbiting aline stars.

If we are to find alien life hiding somewhere in the cosmos, then it’s really handy if we have a guide that tells us where we should look.

As noted by Eric Ford, a professor of astrophysics and one of the co-authors of the new study, an Earth-like planet is defined as being anywhere from three quarters to one-and-a-half times the size of our planet, orbiting its host star every 237 to 500 days.

Those numbers aren’t random and represented an orbital period, which suggests the exoplanet is located with the star’s habitable zone, the “range of orbital distances at which the planets could support liquid water on their surfaces,” as Ford explained it in a press release.

This means that the new analysis of data gathered by the Kepler space telescope is an integral part of our search for Earth-like planets and consequently, alien life.

And precisely the data gathered by Kepler, a space telescope which launched in 2009, tells us there’s a lot of planets out there that are similar to Earth.

The Kepler space telescope used the so-called transit method to discover alien worlds in a distant solar system. During its mission, it observed more than 503,000 stars, looking for “dips in the star’s brightness,” a tell-tale sign that may indicate a planet passed in front of it.

The space telescope’s mission was a total success. Kepler identified more than 2,600 exoplanets revealing that there are more planets than stars in our galaxy, providing astronomers with unprecedented information about our cosmic neighborhood.

Although the Keppler space telescope was retired by NASA in 2018 after it ran out of fuel, it discovered that as much as 20 to 50 % of the stars visible in the night sky have Earth-like planets in the so-called goldilocks zone.

However, the recent estimates were not solely based on the number of exoplanets Kepler found, as the transit method identifies planets only orbiting close to their stars. What if there were planets still in the habitable zone, but further away from their stars?

In order to estimate the real number of alien worlds in our galaxy, the astronomers developed a computer simulation o hypothetical universes comprising stars and planets, based off of a combination of data gathered by Kepler, and the European Space Agency’s Gaia Spacecraft.

The researcher’s program observed the stars as the Kepler space telescope would have.

Then came the magic.

The simulation revealed a previously unseen universe of exoplanets that the Kepler space telescope would have detected, and the kinds of planets orbiting their respected stars.

They could then compare the data to what the real Kepler saw, and estimate the number of Earth-like planets in the habitable zone of their stars.

The results were surprising, as many as 10 billion exoplanets that are similar to our own planet exist in the Milky Way alone.

But even though a planet orbits its star in the habitable zone, it still needs an atmosphere like that of Earth to capture enough heat in order to sustain liquid water on the surface.

But researchers can measure the composition of an exoplanet by calculating the behavior of the star’s light as it passes in front of the exoplanet. We might not be able to observe it directly, but we can still learn a lot from it based on other measurements.

And it is precisely there where Ford’s study comes into play.

If worlds similar to our planet are abundant, then there might as well be enough of them close by for armors to study them with less sophisticated telescopes.

If these worlds are located extremely far away, then the only solution would be to study them with state-of-the-art telescopes.

“Knowing how often we should expect to find planets of a given size and orbital period is extremely helpful for optimizing surveys for exoplanets and the design of upcoming space missions to maximize their chance of success,” said Ford. “Penn State is a leader in bringing state-of-the-art statistical and computational methods to the analysis of astronomical observations to address these sorts of questions. Our Institute for CyberScience (ICS) and Center for Astrostatistics (CASt) provide infrastructure and support that makes these types of projects possible.”