The big news from NASA is that their space exploration mission Voyager 1 has now passed into interstellar space. That means it has gone beyond the border of our own solar system… beyond the influence of our sun.
They have been anticipating this big event for about a year now, but they weren’t quite sure when it would happen, or even how they would know when it did. The area of space influenced by our sun is called the heliosphere. It’s sort of a cloud-like thing, with a lopsided shape and ill-defined edges, that is most notably measured by the reach of solar winds emanating from the nearest star. (our gassy sun) Not unlike how a person can “claim space” in a room by emitting gas.
The outer edge of this, the finish-line ribbon of the race to interstellar space, is called the heliopause. Why did they call it that? Helio if I know! The whole outer edge is defined by a conflict of winds; solar winds coming from the inside bumping into interstellar winds pushing through the no-mans-land of open space. The interstellar winds are travelling at approximately a million miles-per-hour, and slow to a quarter of that when they hit this border of ionized gas. It makes for a lot of turbulence, which is how researchers knew that Voyager was getting close.
It wasn’t until a fortunately-timed solar flare occurred, sending a strong burst of wind out towards Voyager, that they were able to conclude they had crossed the threshold. The strong wind created waves in the plasma surrounding Voyager, which had the proper instrument to measure, and it was the density of this plasma that suggested they were now sitting outside the heliosphere, beyond the domain of our sun.
This is all going on about 18.7 billion (with a B) kilometres from earth. (For comparison, Pluto is only about 6 billion km away) Voyager 1 has enough fuel to stay on its course until about 2020, at which point it will simply wander the stars at the whim of the cosmos.
- Source: NASA Voyager 1 mission update