NASA has found a 'second Earth' that's just like ours.
Otherwise known as 'Earth 2.0', Kepler-452b is the first small planet discovered within the habitable zone orbiting a sun that's almost identical to our own.
Jeff Coughlin, Kepler research scientist at SETI Institute in Mountain View, California said:
"This is the first step to find out the answer to see if we are alone. Yes we may not be able to travel to these planets but our children's children will do. It's a long-term exciting goal."
The discovery "hits right at the heart of what we're trying to do in science at NASA, our mission is to innovate, discover, explore and inspire." said John Grunsfeld, associate administrator for NASA's Science Mission Directorate in Washington.
Despite the sun being 20 per cent bigger, 20 per cent brighter, Kepler-452b has a radius that's 60 per cent larger than Earth's and has a surface that's likely very rocky.
It has a mass that's five times Earth's, with a gravity that's twice as strong. Don't panic though, you'll still be able to walk on the surface once you've 'lost a few pounds'.
John Jenkins, Kepler data analysis lead at NASA's Ames Research Center in Moffett Field, California, points out that while life would be tough at first, after a few generations, humans would actually adapt to conditions on the planet.
In terms of its geology Kepler-452b probably has an atmosphere of thick cloud and will likely be potholed with volcanoes.
Is There Alien Life On Kepler-452b?
What makes this planet so important is the amount of energy that it receives. Kepler-452b's size means that proportionately it receives the same amount of energy that Earth does needed to foster a habitable planet.
"If you travel to this star with an arkful of plants, we'd expect based on our understanding of planetary system formations there would be a lot of raw materials for you to use, but more importantly for plants the sunshine from this star is very similar to the sunshine from our star, so the plants would photosynthesise just like on Earth."
Kepler-452b's passage around the Sun is similar to that of Earth's, a year takes around 380 days compared to our 365.
With six billion years of life within the habitable zone NASA believes 452b has had "considerable time and opportunity for life to exist".
That's right, there's every chance that life existed on this planet.
Kepler-452b's story is something a sad one though, it has already spent billions of years potentially having life, that's nearly 2 billion years older than Earth itself.
The announcement was made during a live teleconference where authors of the paper spoke about the significance of the event.
Twitter reactions have understandably been positive:
Kepler's discoveries are unique in that much of the data has already been collected, scientists are now having to spend years trawling through all the data in the hopes of finding the right pieces.
Kepler: Searching For Earth 2.0
The Kepler Telescope mission began in 2009 and has already discovered thousands of planets but NASA, said today's announcement could unveil "something people have dreamed about for thousands of years."
Artist's impression of an Earth-like planet orbiting a star near the end of its life surrounded by a shell of expanding gas
So far, the search for alien planets has found 4,661 candidate planets and 1,028 planets.
Illustrations of the newfound exoplanets pictured next to Earth. Click on the image to enlarge
Last year, NASA announced the discovery of an "Earth-size planet orbiting a star in the "habitable zone" -- the range of distance from a star where liquid water might pool on the surface of an orbiting planet."
At the time, Elisa Quintana, research scientist at the SETI Institute said: "We know of just one planet where life exists -- Earth.
"When we search for life outside our solar system we focus on finding planets with characteristics that mimic that of Earth."
The process of discovering planets just like ours is painstakingly complex that require scientists to measure the change in the brightness of distant stars to determine "a planet's orbit, distance from its star and its size."
The journey so far has not been an easy one. In April 2013, just fours years after the Kepler mission began, NASA had to deal with a fault in the spacecraft's stabilising systems, which meant the telescope could not orientate itself to observe stars with sufficient accuracy.
Eight months later, NASA had to give up on fixing the troubled aircraft.
However, the setbacks don't appear to have stemmed the stream of planet-centric discoveries.
In January, another eight planets, including two very earth-like ones, were found.
By "small" astronomers mean planets with less than twice the Earth's diameter. "Most of these planets have a good chance of being rocky, like Earth," said lead scientist Dr Guillermo Torres, from the Harvard-Smithsonian Centre for Astrophysics in Cambridge, US.
The two most Earth-like planets, known as Kepler-438b and Kepler-442b, both orbit red dwarf stars that are smaller and cooler than the Sun. With a diameter just 12% bigger than Earth, Kepler-438b has a 70% chance of being rocky, the scientists have calculated. Kepler-442b is about one-third larger than Earth, and the likelihood of it being rocky is around 60%.
To be in the habitable zone, also known as the "Goldilocks zone", a planet must be not too hot or too cold and receive roughly as much sunlight as Earth. Too much heat from its star, and any water would boil away as steam. Too little, and the water would freeze solid.
"For our calculations we chose to adopt the broadest possible limits that can plausibly lead to suitable conditions for life," Dr Torres added. Kepler-438b receives about 40% more light than the Earth giving it a 70% probability of having a habitable zone orbit. In comparison, baking hot Venus has twice as much.