steorra: Jupiter's moon Europa (europa)
[personal profile] steorra posting in [community profile] astronomy
I keep seeing articles about how Voyager 1 is leaving the solar system, or about to leave the solar system, or may just have left the solar system. An example is a science blog post titled More evidence that Voyager has exited the solar system.

These articles are talking about a real and interesting phenomenon, but I find the description of it as "leaving the solar system" misleading.

What they are primarily talking about is Voyager leaving the sun's heliosphere, the region of space affected by the charged particles of thesolar wind. Outside the heliosphere is the interstellar medium. Passing the heliopause between the heliosphere and the interstellar medium is crossing a significant boundary between a kind of space that is heavily influenced by the sun and one that isn't. So it is a significant event that Voyager 1 is passing this boundary, and in the process giving us evidence about the location of the boundary and what conditions are like at it and on either side of it.

Voyager 1 is currently about 122 astronomical units (au) from the sun, or 122 times earth's distance from the sun. That's a long ways away, but there are still many objects in the solar system whose orbits take them out that far; not only many comets, but also Sedna, which goes as far as 940 au from the sun at its most distant. And the Oort cloud, a hypothesized reservoir of comets that have never yet come close to the sun, is hypothesized to be between around 5000 and 50,000 au from the sun. All these orbits are still orbiting the sun, and thus still part of the solar system. It seems misleading to me to say that Voyager 1 is leaving the solar system when it's still well within the orbits of many things orbiting the sun.

But crossing the heliopause is still neat and noteworthy.
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