Creeping Closer to the “Edge” of the Solar System
The two Voyager spacecraft have always occupied a soft spot in my heart because they were the first ones I ever reported on in my days as a science journalist. They opened up our eyes to what actually exists in the outer solar system around the planets Jupiter, Saturn, Uranus, and Neptune. For the first time, those gas and ice giants became recognizable worlds, with moons and rings and unusual weather patterns.
The Voyagers are on one-way trips out of the Solar System. Voyager 1 is literally pushing the envelope of the Sun’s influence, currently transiting through a region called the “magnetic highway”. To understand that term, think of the Sun as blowing a bubble of gas out to interstellar space. Like any bubble (or a balloon), it has a thin surface. The region inside the bubble is threaded with the Sun’s magnetic field lines.
Voyager 1 has been slowly exploring the outermost regions of the bubble. In 2004, it passed a shockwave known as the “termination shock”. This is where solar wind suddenly slows down and becomes more turbulent. In 2010, Voyager then passed into an area called the “stagnation region” where the outward velocity of the solar wind slowed to zero and sporadically reversed direction.
On Aug. 25, 2012, Voyager 1 entered the depletion region, where the magnetic field acts as a kind of magnetic highway that lets energetic ions from inside the heliosphere escape out, and cosmic rays from interstellar space zoom in. (To learn more about how this region acts as a magnetic highway, click here and read more here about today’s Voyager 1 announcement.)
As Voyager 1 zooms out on its endless journey, eventually it will cross the heliopause—the “skin” of the bubble blown out by the Sun. After that, it’s clear sailing to the next flyby of a celestial object, the star Gliese 445. However, that won’t happen for about 40,000 years. Chances are that Voyager 1 will be unable to tell us anything about it (provided we’re still around), since its systems are slowly deteriorating, and astronomers will begin shutting down most of its subsystems in the next few years. Still, it will send signals as long as its power holds out, as it transits interstellar space at the fastest speed relative to the Sun of any human-made object sent to space.
If you’ve never read about the Voyager missions to the outer solar system, they provide quite a tale and one well worth knowing. So, check here and here and here to learn more about these amazing spacecraft and the discoveries they helped planetary scientists make.