astroengine writes "After a 35-year, 11-billion mile journey, NASA's Voyager 1 spacecraft left the solar system to become the first human-made object to reach interstellar space, new evidence from a team of scientists shows. 'It's kind of like landing on the moon. It's a milestone in history. Like all science, it's exploration. It's new knowledge,' long-time Voyager scientist Donald Gurnett, with the University of Iowa, told Discovery News. The first signs that the spacecraft had left the solar system's heliopause was a sudden drop in solar particles and a corresponding increase in cosmic rays in 2012, but this evidence alone wasn't conclusive. Through indirect means, scientist analyzing oscillations along the probe's 10-meter (33-foot) antennas were able to deduce that Voyager was traveling through a less dense medium — i.e. interstellar space." You can watch NASA's briefing on the probe's progress here.