Voyager 1

So, you've probably heard that recently the Voyager 1 space probe entered a new region of space. At first we were told that it had indeed left the solar system altogether and entered interstellar space, apparently this rumour got started by the American Geophysical Union (AGU). But NASA then sent out a press release saying that it was their opinion that the probe had in fact not yet left our system. I doubt it is very easy to determine where the boundary of our solar system is from data being sent back from a probe launched over 30 years ago, but it seems that there are a couple clues.



















1. Up until now the probes (I say probes because there is a Voyager 2, but it is some millions of kilometers behind V1 and going in a different direction) have been speeding through a stream of cosmic rays, a solar wind of particles of hydrogen and helium flung out from the Sun for billions of kilometers in all directions. Detecting changes in the hydrogen and helium offers one clue as to the location of the probe.

In the summer of 2012, the solar wind surrounding Voyager 1 came to a dead stop, a boundary known as the heliopause, and by some definitions that should have been it, the ship should have been out. And then, capriciously, it just started up again. NASA and the AGU agree that the end game will truly be upon us when the wind stops for good and Voyager punches through the so-called heliosheath, when outward-flowing energy drops to effectively zero and inward-flowing interstellar energy spikes. Those findings were confirmed by the study the AGU released yesterday, leading to the somewhat premature announcement. (link)

2. It was a "premature announcement" because the probe will have not truly left the solar system until it ceases to be influenced by the Sun's magnetic field and is rather more affected by interstellar magnetism. 

the magnetic field that surrounds the ship will have to change direction, indicating that solar magnetism is yielding to the deeper magnetism of space. Last December, the fields began interlocking and lining up — putting Voyager on what Stone calls the magnetic highway. But the ship hasn’t taken the exit ramp to deeper space yet. “A change in the direction of the magnetic field is the last critical indicator of reaching interstellar space and that change of direction has not yet been observed.”

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Pretty interesting stuff. Also interesting are the golden phonograph records carried by both probes. Each record has an assortment of goodies for any technologically advanced species to peruse should they happen upon the probe (which won't be for a long time yet as they are still very far from any other planetary system.)

There are directions for use, greetings in 55 languages, a variety of music and sounds, and a bunch of pictures - scenes from Earth.

For example, mathematical definitions: