By Keerthi Chandrashekar / ( | First Posted: Dec 29, 2012 08:56 PM EST

(Photo : J. Pinfield for the RoPACS network at the University of Hertfordshire)

**Correction: The article below refers to exoplanets as planets outside of our solar system that lie in a star's habitable zone. An exoplanet is actually any planet outside of our solar system, inside or outside of a star's habitable zone.

Finding a planet like ours has been one of the cornerstones of space exploration ever since we first broke through our atmosphere. While a true Earth-like planet has yet to be found, experts are marking 2013 on their calendar as the year we finally stumble across one in the void of space.

Scientists have logged in plenty of possible entries, but none of them seem to share two key characteristics with Earth: size and surface temperature. With those two traits lined up, a planet would have a higher chance of containing liquid water and being hospitable for life as we know it.

Still, scientists are hopeful that with the ever-increasing rate of discoveries, a planet that is actually similar to ours can be found in the near future.

"I'm very positive that the first Earth twin will be discovered next year," said Abel Mendez, who runs the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo.

Much of the scientific effort to find an alien Earth has thus far been focused on identifying planets that lie in the habitable zone. The habitable zone is a specific range of distance that a planet must be from a star in order to not be too hot, or too cold, for liquid water to form.

Plenty of planets that lie in the habitable zone, known as exoplanets, have been found since the first one was discovered in 1995, but none have a size or surface temperature close enough to Earth to excite scientists. A large part of this has to do with the fact that many of these exoplanets haven't been studied in enough detail due to their distance from us, but scientists are hoping that will all change with new technologies.

One these technologies, the High Accuracy Radial velocity Planet Searcher HARPS, lets astronomers zero in on tiny gravitational fluctuations caused by a planet on its parent star.

"HARPS should be able to find the most interesting and closer Earth twins," Mendez wrote to in an email. "A combination of its sensitivity and long-term observations is now paying off."

Of course, even if a truly Earth-like planet is found, we won't have the technology to actually inhabit it for a very long time. Still, in the famous words of astronaut Neil Armstrong, it will be "one small step for man, one giant leap for mankind."

Watch a video on the 10 most amazing exoplanets:

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