Thirty-six years ago, NASA launched two space probes to explore the planets in our solar system.

Now scientists say Voyager 1 has reached an historic frontier.

It is the first manmade spacecraft to leave the solar system and cross into interstellar space.

SOUNDBITE: ED STONE, VOYAGER PROJECT SCIENTIST SAYING:

"Now, what does it mean to reach interstellar space? Well first of all, we got there. I mean, this is something we all hoped when we started on this 40 years ago, that this would happen but none of us knew how big this bubble was, and none of us knew anything could last as long as the two Voyager spacecraft."

NASA scientists say the Voyager 1 is 12 billion miles from the sun.

SOUNDBITE: GARY STARK, VOYAGER PROJECT SCIENTIST SAYING:

"We've exited the material created by the sun and we're truly in an alien environment. The material in which Voyager finds itself is not created by the sun. It's created in fact by our neighboring stars, superno