1189: Voyager 1
Voyager 1 is a U.S. space probe launched in 1977 to study the outer reaches of the Solar System and beyond. Popular press has on several occasions announced that it "has left the solar system" at each point when a boundary has been confirmed or a major event has taken place. This underscores the fact that there is no strictly defined and recognizable boundary of the solar system, or at least we haven't found one yet.
On the day of this comics release (2013-03-22) it was announced that Voyager 1 had entered a new region of space. At this point Voyager 1 had passed through the Heliopause and entered the Interstellar medium, although this latter was first confirmed about half a year later in September 2013.
The chart shows that Voyager 1 has left the Solar System 22 times, but in the title text only 16 are mentioned.
The title text lists several such possible boundaries, (and how many times Voyager 1 has passed them) together with fictive humorous ones:
 Real boundaries
- Three times:
- The termination shock—the point in the heliosphere where the solar wind slows down to subsonic speed (relative to the star) because of interactions with the local interstellar medium. When exactly Voyager 1 passed the Termination shock is not clear and on Wikipedia there is given dates of 2003, 2004 and 2005. The final estimate was that it happened late in 2004. (Thus fitting with three times).
- The heliopause—the theoretical boundary where the Sun's solar wind is stopped by the interstellar medium. It was first reported in 2012 that Voyager 1 had reached the Heliopause, but first on the day of this comics release was it officially announced that it had passed through to the interstellar medium. (Thus fitting with two times).
- Once only (Each):
- The heliosphere—a region of space dominated by Earth's Sun, a sort of bubble of charged particles in the space surrounding the Solar System—we live inside this region. At its boundary there are three named borders which are the real ones mentioned before and after this in the title text. From inside to out they are: The termination shock, the heliosheath and the heliopause. The reason the other two are mentioned first is that they have occurred more than once, and the list begins with those for that reason. As these other three borders are also part of the heliosphere, with the heliopause being the outer border of the heliosphere, then Voyager 1 will have left the heliosphere at the same time as it left the heliopause.
- The heliosheath—the region of the heliosphere beyond the termination shock. It was confirmed that Voyager 1 passed through this at the end of 2010, so this occurred two years before the Heliopause was reached. But since it only happened once, it is mentioned after the first two, and maybe after the heliosphere because it is inside this region?
 Fictional boundaries
- Heliodrome—yet another composition of helios "sun," here together with dromos "course". There is no astronomical object with this name, but it has been used variously in other contexts. One that became famous is a sports hall which was used as a concentration camp in the Bosnian war, see Heliodrom camp.
- Auroral discontinuity—another fictitious astronomic object, for auroral see Aurora (astronomy).
- Heaviside layer—a layer of ionized gas occurring between roughly 90–150 km (56–93 mi) above the ground in the Earth's atmosphere. Popularly recognized for its use as a reference to Heaven in the writings of T. S. Eliot adapted into Andrew Lloyd Webber's musical Cats.
- Trans-Neptunian panic zone—this fictional zone combines the word from two subjects: "Trans–Neptunian" is used in astronomy to describe stuff that occurs beyond the planet Neptune. In Outdoor education the "panic zone" is the opposite of the comfort zone when trying to learn new stuff.
- Magnetogap – part of an ignition system.
- US Census Bureau Solar System statistical boundary—a fictitious boundary supposedly defined by the United States Census Bureau, similarly to how it defines census areas for the purpose of processing statistical data about regions in the United States. In this case, the Bureau's boundary for determining the population of the solar system.
- Kuiper gauntlet—this is a play on the Kuiper belt, which is a region of the Solar System beyond the planets, extending from the orbit of Neptune (at 30 AU) to approximately 50 AU from the Sun, notable for being full of asteroids; replacing the word "belt" with "gauntlet (glove)" (often spelled 'gantlet') which is a protective glove as well as "gauntlet (punishment)" which is a medieval punishment where one would be forced to run through two lines of men who would hit the punishee.
- Oort void—refers to the Oort cloud, a gigantic "cloud" of materials (mainly composed of ice) which ends around a light-year from The Sun and is deemed the (current) "edge" of the solar system. The "void" may be pun on density of that "cloud" - the number of bodies in it may be huge, but given its size, it's mostly empty.
- Crystal sphere holding the fixed stars—this refers to historical ideas about the universe, particularly the Ptolemaic system, in which the stars were supposed to be fixed on a large crystal sphere around the Earth. It might also be referencing "The Crystal Spheres", a short story by David Brin, in which humanity's first interstellar ship shatters a previously undetected, protective barrier around the solar system. It may also be a reference to the Dungeons and Dragons setting "Spelljammer".
- Total count above reaches 16 exits from the solar system vs. 22 in the comic itself.
See also Voyager over the “heliocliff,” but Solar System transition mysterious on Ars Technica.
- [A heading at the top of a white panel, then a line and below this 22 tally marks in two rows, four times five (three of these at the top) and then two extra.]
- Number of times Voyager 1 has left the Solar System
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