Data From Voyager 2 Following Her Sister Into Interstellar Space

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There's a fair bit of information in the article, as well as a few videos. I only quoted the first intriguing fact. I've also constrained the size of the image--please open it in its own window if you'd like to see it full size.

"Voyager 2 Reaches Interstellar Space. Here's What the Spacecraft Finds." | LiveScience

Image Credit: NASA /JPL-Caltech

Humanity's second taste of interstellar space may have raised more questions than it answered.

NASA's Voyager 2 spacecraft popped free of the heliosphere — the huge bubble of charged particles that the sun blows around itself —  on Nov. 5, 2018, more than six years after the probe's pioneering twin, Voyager 1, did the same.

The mission team has now had some time to take stock of Voyager 2's exit, which occurred in the heliosphere's southern hemisphere (as opposed to Voyager 1, which departed in the northern hemisphere). In a series of five papers published online today (Nov. 4) in the journal Nature Astronomy, the researchers reported the measurements made by the probe as it entered interstellar space.

These data are full of surprises. For example, Voyager 2 traversed the heliopause — the boundary between the heliosphere and interstellar space — when the probe was 119 astronomical units (AU) from the sun. (One AU is the average Earth-sun distance, which is about 93 million miles, or 150 million kilometers.) Voyager 1 made the crossing at nearly the same distance, 121.6 AU.

This consistency is "very strange, in the sense that one [Voyager 2's crossing] occurred at the solar minimum, when the solar activity is the least, and the other one occurred at the solar maximum," Stamatios Krimigis, lead author of one of the new Voyager 2 papers, said during a teleconference with reporters last week, referring to the sun's 11-year activity cycle.

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Fascinating article.

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Checking the political news at The Hill, I came across a science story (a rare thing on that site). It referred to a study by scientists at the University of Iowa that the article above didn't describe. However, that article did quote Don Gurnett, the lead author of the Iowa study, and includes an access token link to the full paper describing the study (third paragraph from the bottom) if you care to check it out. The full paper is behind a paywall elsewhere.

The story at The Hill is short on actual science of course--it's mostly fluff. It did link to an article about the Iowa study, however.

"Voyager 2 reaches interstellar space: Scientists detect plasma density jump" | PhysOrg

In a new study, the researchers confirm Voyager 2's passage on Nov. 5, 2018, into the ISM by noting a definitive jump in plasma density detected by an Iowa-led plasma wave instrument on the spacecraft. The marked increase in plasma density is evidence of Voyager 2 journeying from the hot, lower-density plasma characteristic of the solar wind to the cool, higher-density plasma of interstellar space. It's also similar to the plasma density jump experienced by Voyager 1 when it crossed into interstellar space.

"In a historical sense, the old idea that the solar wind will just be gradually whittled away as you go further into interstellar space is simply not true," says Iowa's Don Gurnett, corresponding author on the study, published in the journal Nature Astronomy. "We show with Voyager 2—and previously with Voyager 1—that there's a distinct boundary out there. It's just astonishing how fluids, including plasmas, form boundaries."

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"Cool plasma" is a relative term. From the abstract of yet another paper on the Voyager 2 measurements of the interstellar plasma:

The VLISM [very local interstellar medium] is variable near the HP [heliopause] and hotter than expected. Voyager 2 observations show that the temperature is 30,000–50,000 K, whereas models and observations predicted a VLISM temperature of 15,000–30,000 K.

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Just goes to show that nature plays by its own rules, not our expectations.