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This is a difficult number to know for certain, since we can only see a fraction of the Universe, even with our most powerful instruments. The most current estimates guess that there are 100 to 200 billion galaxies in the Universe, each of which has hundreds of billions of stars. A recent German supercomputer simulation put that number even higher: 500 billion. In other words, there could be a galaxy out there for every star in the Milky Way.

"Astronomers have a mind-blowing new theory: that there are 17 billion Earth-sized planets in our galaxy. They don't yet know how many of these worlds are in habitable zones, but the implications of this discovery are amazing. So much that some claim the "quest for a twin Earth is heating up." Simply put: If there are 17 billion Earth-sized worlds in our galaxy, it's clear that the Universe is bubbling with life."

As you probably know, astronomers use the distance that light travels in a year as a standard measuring stick for calculating the largest distances in the Universe. The nearest star to Earth, Proxima Centauri, measures 4.22 light-years from Earth. The center of the Milky Way Galaxy is 26,000 light-years away. The nearest large galaxy, Andromeda, is 2.5 million light-years away.

A collection of Nat Geo photos of galaxies.

What does it mean for a galaxy to be the most distant galaxy disovered? The numbers are staggering. Here's what you need to know.

"The Hubble space telescope has captured an image of a "barred spiral" galaxy that could help us better understand our own Milky Way. Most of the known spiral galaxies fall into this "barred" category - which are defined by the pronounced bar structure across their centres. The presence of this structure may be an indication of a galaxy's age"

Just a week after NASA scientists announced their certainty of finding alien life within the next 20 years, a team of scientists say they've found no obvious signs of advanced extraterrestrial life after searching 100,000 galaxies.

A nice Nat Geo map showing the Milky Way Galaxy and our position inside of it.

"There could be many billions of planets not much bigger than Earth circling faint stars in our galaxy, says an international team of astronomers. The estimate for the number of "super-Earths" is based on detections already made and then extrapolated to include the Milky Way's population of so-called red dwarf stars."

"The Milky Way hosts at least 17 billion Earth-size alien planets, and probably many more, a new study reveals. Astronomers have determined that about 17% of stars in our galaxy harbor a roughly Earth-size exoplanet in a close orbit. Since there are 100 billion or so stars in the Milky Way, that works out to a minimum of 17 billion small, rocky alien worlds, or an Earth-size planet around one of every six stars. And there are probably many more such planets orbiting at greater distances from their stars, some of which may even be "alien Earths" capable of supporting life as we know it."

Venus may have once possessed strange oceans of carbon dioxide fluid that helped shape the planet's surface, researchers say.

PLAY VIDEO
60 Billion Planets Could Harbor Life
For years, we've believed that around 2 billion planets in the galaxy are able to support alien life. But what if we were wrong? Anthony discusses how new knowledge of the 'Goldilocks Zone' could mean life on up to 60 billion planets.
Venus is often described as Earth's twin planet because it is the world closest to Earth in size, mass, distance and chemical makeup. However, whereas Earth is a haven for life, Venusis typically described as hellish, with a crushing atmosphere and clouds of corrosive sulfuric acid floating over a rocky desert surface hot enough to melt lead.