Voyager over the "heliocliff," but Solar System transition mysterious
It's left the solar wind behind, but we're not sure what region it's in.
Where does our Solar System end? If you define it in terms of the Sun's gravitational influence, then it's the edge of the Oort cloud, a collection icy bodies that stretches over two light years from the Sun. You could also place it at the orbit of the last dwarf planet that roams the Kuiper belt. But if you want to define it where the Sun's energy directly affects the environment, then you'd place it at the edge of the heliosheath, where the solar wind and the Sun's magnetic field fall off, and the environment is dominated by the energetic particles of the interstellar medium.
That boundary, called the heliopause, was approached by the most distant man-made object around: Voyager 1. In December, researchers held a press conference to announce that, rather than crossing a clean boundary, the probe had entered a region near this edge that nobody had predicted. Today, the paper describing these results was released, and thanks to some public relations confusion, many outlets reported that the probe had left the Solar System entirely.
The evidence of a boundary is very clear in the chart shown below, which maps the particles that Voyager has recorded in its environment over the last year. In blue are low-energy protons emitted by the Sun itself. These fluctuated for a few weeks before dropping off a cliff by over 99 percent. The authors of the paper have termed this transition the "heliocliff."
As Voyager 1 approached the cliff, high energy electrons (red) and protons (black) were rising; these come from the interstellar medium and are largely blocked by the force of the solar wind. Once the cliff is passed, however, these energetic particles reach new highs and stay here. By this measure, Voyager 1 has left a key area of solar influence and is now sampling the interstellar medium for the first time. The authors of the paper are so excited by this that they use the terms "extraordinary," "remarkable," and "holy grail" to describe the transition - that sort of terminology doesn't appear often in the scientific literature.
Enlarge / After several partial crossings, Voyager 1 is clearly experiencing the interstellar medium.Geophysical Research Letters
But has Voyager actually passed beyond the heliopause? The authors argue that it has: "If [these] intensities continue to remain at their present levels, then indeed this 'heliocliff' region displays many of the properties of a 'classical' heliopause, perhaps a much more impressive barrier to inward and outward transport of energetic particles than would have been anticipated." However, what's missing is a similar transition in the magnetic field lines from the Sun. Those were expected to change at the heliopause as well, and until they do, all we can say is that Voyager is passing through an unpredicted region at one of the edges of our Solar System.
Unfortunately, a press officer seems to have gotten a bit ahead of the data, as the initial announcement of the paper's release was entitled "Voyager 1 has left the solar system, sudden changes in cosmic rays indicate." That led to a predictable number of news stories that echoed this language. Since then, however, the American Geophysical Union has updated its release, which now says only that "Voyager 1 has entered a new region of space." Which is something we knew as far back as the press conference in December.
The paper at least puts the data in front of other scientists. And its acknowledgements contain a touching tribute to one of the original Voyager team members, which we'll quote in its entirety:
This article was conceived by our Voyager colleague, Frank McDonald, who is no longer with us. Frank, we have been working together for over 55 years to reach the goal of actually observing the interstellar spectra of cosmic rays, possibly now achieved almost on the day of your passing. You wanted so badly to be able to finish this article that you had already started. Together we did it. Bon Voyage!
Geophysical Research Letters, 2013. DOI: 10.1002/grl.50383 (About DOIs).
wesley96Ars Tribunus Militum
peppeddu wrote:35 years (and counting) without a reboot, computer freeze, hardware failure or software update.Try that today Actually, the twin craft Voyager 2 did have a glitch, so it received a software update.... in 2010. ... 2_999.htmlYeah. NASA guys remotely patched a then-33-year old craft 14 billion km away successfully.