Some readers may remember back in July that some scientists at NASA believed that the Voyager 1 probe had left the solar system, but there was still some debate about the issue. Now, just over two months later, there is more evidence that it not only is beyond the edge of our solar system, but that it may have left as early as August 2012. (The official news release can be found here.)

Unfortunately there is no clear delineation of the boundary between the solar system and interstellar space. However there are some indicators of the transition, in the form of the sun's magnetic field and its effects on particles from our own solar system and on interstellar particles and plasma. As such the best way to determine when Voyager left would be to use plasma detectors on the probe to measure density and other parameters. Unfortunately after 36 years of travelling through space, Voyager's plasma detectors are not working which limited engineers and scientists ability to determine the exact point when it left.

However our Sun gave the teams a little assistance, by ejecting a large solar flare in March 2012. It traveled for just over a year, and hit the Voyager probe in April 2013 causing the surrounding plasma to oscillate in response. This motion caused electromagnetic waves that could be detected by antennae on the probe, and by analyzing the signal scientists could deduce the plasma density. The density turned out to be nearly forty times greater than what astrophysicists predict would exist at the edge of the heliosphere, and is closer to the expected density in interstellar space.

Using this measurement, and a weaker signal from November 2012, NASA was able to interpolate the date of Voyager exiting the solar system to August 2012. Some readers may recall that August 25, 2012 saw the Voyager probe detect changes in the flux of particles which provided the first major evidence of entering interstellar space.

And so with these new results, it has become generally accepted that after 36 years of travel Voyager 1 is now officially the first man-made object to pass into interstellar space. It is quite an achievement for mankind and the spirit of exploration!