What does it mean to us homo sapiens ?

Whenever the first Earth twin is confirmed, the discovery will likely have a profound effect on humanity.

"We humans will look up into the night sky, much as we gaze across a large ocean," Marcy told SPACE.com via email. "We will know that the cosmic ocean contains islands and continents by the billions, able to support both primitive life and entire civilizations."

Marcy hopes such a find will prod our species to take its first real steps beyond its native solar system.

"Humanity will close its collective eyes, and set sail for Alpha Centauri," Marcy said, referring to the closest star system to our own, where an Earth-size planet was discovered earlier this year.

"The small steps for humanity will be a giant leap for our species. Sending robotic probes to the nearest stars will constitute the greatest adventure we Homo sapiens have ever attempted," Marcy added. "This massive undertaking will require the cooperation and contribution from all major nations around world. In so doing, we will take our first tentative steps into the cosmic ocean and enhance our shared sense of purpose on this terrestrial shore