Storygram: Andrew Grant’s “At last, Voyager 1 slips into interstellar space”

The Storygram series, in which professional writers annotate award-winning stories to illuminate what makes a great science story great, is a joint project of The Open Notebook and the Council for the Advancement of Science Writing. It is supported by a grant from the Gordon and Betty Moore Foundation. 

Andrew Grant is the online editor at Physics Today. His story below won the American Geophysical Union’s 2014 David Perlman Award for Excellence in Science Journalism. This annotation was done by Marguerite Holloway and students in the Columbia University Graduate School of Journalism’s M.A. Science Concentration: Tryggvi Adalbjornsson, Guia Baggi, Mariana Lenharo, Maya Miller, Greta Moran, Disha Shetty, and Elizabeth Whitman. It is co-published at The Open Notebook. 

Humankind has officially extended its reach to the space between the stars.In merely 12 words, Grant has managed not only to summarize the contents of the story—a classic notion of a good lede—but also to encapsulate the story’s significance. For millennia, the human race has been busy exploring its home planet. For decades, humans have explored the solar system. Now, a new age of exploration has begun—that of interstellar space. Also, look how beautifully this idea is framed within the structure of the sentence. By starting with the word “humankind” (relating immediately to us, the readers) and ending with “the stars” (denoting the ultimate frontier, of which we have dreamt since before the dawn of civilization), Grant emphasizes the story’s vast context. Voyager 1, this distant piece of metal, relates directly to one of the fundamental aspects of the human condition.

NASA’s Voyager 1 spacecraft exited the vast bubble of particlesThis vivid, familiar language helps the reader envision something not of our world. We may not know what’s out there at the edges of the solar system, but we know what a bubble looks like, and we can imagine one filled with some kind of particles. that encircles the sun and planets on August 25, 2012, mission scientists report September 12 in Science. At the time, Voyager was about 18.2 billion kilometers from the sun, or nearly 122 times as far from the sun as Earth.Numbers can easily halt the flow of a story, but we usually feel better when a number carries with it a familiar point of reference. Although none of us have traveled to the sun, we have at least a hazy hunch of how long it would take to get there. Grant’s comparison is essential to our understanding the distance Voyager 1 has traveled. Also, “122 times as far from the sun as Earth” is a translation of a technical and opaque unit of measurement, the astronomical unit—the mean distance between the center of the earth and the center of the sun. In a big favor to us, Grant gives the measurement in common language, sparing us from having to stop reading to make sense of what an astronomical unit is.

“This is the beginning of a new era of exploration for us,” says Edward Stone of Caltech, who has headed the Voyager mission since 1972. “For the first time, we are exploring interstellar space.”After giving us the basic facts, Grant wisely goes straight to the source to confirm and expand on what was implied in the very first sentence of the article. He’s given us an authoritative voice to back up the dramatic claim that’s at the center of the account. Now, he can go on and tell us the whole story.

Confirmation of Voyager’s interstellar exploits came after determining that the probe is surrounded by a relatively dense fog of galactic particles rather than a thin mist of solar ones.It’s a lovely image. Even if you can’t really understand the difference between solar and galactic particles, this sentence gives you the idea that it must be similar to passing from a thin mist to a dense fog, and that the fundamental nature of the surrounding matter has changed. It was a tricky measurement that required patience, clever detective work and a heavy dose of luck.This sentence is simultaneously informative and engaging, giving the reader a realistic sense of how painstaking scientific determinations can be, while also creating a sense of narrative tension by casting such determinations as a blend of detective work and sheer chance. (Later in the story, Grant deftly revives the detective theme.)

NASA launched Voyager 1 and 2 in 1977 to explore the outer planets, but from the beginning Stone’s team hoped the probes would survive long enough to investigate the region of space where our star’s dominance finally wanes. The sun unleashes a flood of hot, charged particles called plasma that jets out in all directions.It’s easy to picture this “flood.” Grant’s pithy description makes understandable something that would require a lengthy technical detour to explain fully. The plasma forms a bubble called the heliosphere that is tens of billions of kilometers in diameter. Over the last decade, the solar plasma around Voyager 1 has thinnedThe language immediately makes the reader recall the thin mist described above, creating a consistent lexicon that exemplifies the careful construction of the story and that builds on readers’ growing understanding. as the spacecraft hurtles toward the edge of the bubble at more than 60,000 kilometers per hour. Astronomers have been waiting for Voyager to cross this boundary — the heliopause, where solar particles give way to even speedier particles ejected by other stars — and enter interstellar space.This sentence widens the lens to look beyond Voyager 1, providing a touch of historical context and a larger sense of what else is going on out there.

The first evidence that Voyager had reached that boundary appeared on July 28, 2012, when the number of solar particles measured by Voyager plummeted. But the particle count rebounded a few days later. Three similar dips and recoveries occurred in the following weeks until August 25, when solar particles disappeared for good (SN Online: 6/27/13). The solar particle measurement, combined with a surge in higher-energy particles from other stars, suggested that Voyager had exited the heliosphere and reached the promised land. Several well-publicized studies made that claim.In the previous paragraph, Grant built up great expectations for his readers about whether Voyager 1 would be able to cross the boundary of the heliosphere and suggested how exciting that would be. In this paragraph, that expectation is fulfilled—Voyager may well have reached “the promised land”—but only after several false alarms. Recounting those false alarms adds drama to the story.

Stone and his colleagues resisted that conclusion.This is the opposite of what the reader would expect after the previous paragraph, which left the impression that the case was all but closed. Reversing the reader’s expectation triggers curiosity: Why in the world was Stone so skeptical, even when his colleagues were convinced? They lacked evidence of what they thought would be the key signature of interstellar space: a shift in the direction of the magnetic field. Solar plasma produces a distinctive magnetic field because it all comes from the same source; scientists expected that the field would shift in interstellar space, where particles flit around in all directions. Despite the particle evidence that Voyager had departed the heliosphere, the magnetic field direction remained constant. “We felt we did not have the smoking gun to say that we had left the solar bubble,” Stone says.This quote echoes the idea of the mystery introduced above and nicely illustrates that research is usually not as simple as a “smoking gun.”

What the Voyager team needed was another independent measurement to confirm the story implied by the particle data. One option was to prove that Voyager was surrounded by cold, dense plasma from interstellar space rather than hot, wispy plasma from the sun.The descriptive yet simple terminology allows the reader to engage with dense and complex material and to understand the major differences between these two environments. Such a measurement would have been straightforward except that Voyager 1’s plasma instrument stopped working somewhere near Saturn 33 years ago.This last sentence packs a surprise, heightening our appreciation of the challenges the researchers face: How will they solve the mystery if critical equipment is offline? By revealing this detail here, Grant maintains narrative tension, pulling us along.

Donald Gurnett, a Voyager scientist at the University of Iowa, found a way to get the measurement anyway. Poring over data from another instrument on the spacecraft, Gurnett discovered that in April 2013 a blast wave from the sun, the same kind that can cause solar storms on Earth, had reached Voyager’s neck of the woods and jostled electrons in the surrounding plasma. It was the first such energetic solar shock in nine years. “In that sense we were lucky,” Stone says.This paragraph explains the work that led to the discovery, but avoids getting into the weeds. For example, the phrase “jostled electrons” brings to mind a clear image so Grant doesn’t have to get into the technical details. In just three sentences, Grant tells us about the work and luck involved in reaching the conclusion about the Voyager’s location. The phrase “neck of the woods” helps us connect with and conceptualize a faraway place and makes it feel familiar, even though it’s light-years away.

Gurnett then used the frequency of the electron vibrations to calculate that plasma surrounding Voyager 1 was about 50 times as dense as scientists would expect inside the heliosphere, a sign that the spacecraft had entered interstellar space.This sentence is a clear, concise explanation of the science supporting the main finding. Grant distills what was almost certainly a complex set of calculations down to the most fundamental result: “50 times as dense.” And he elegantly weaves the finding into the narrative, letting us watch over Gurnett’s shoulder as he performs this key analysis.

“The study very definitively shows that we’re in the interstellar medium,” says Gary Zank, a space physicist at the University of Alabama in Huntsville who was not involved in the research. “There’s no way of producing a density of that size within the heliosphere.”

Not everyone agrees, including a few holdouts on the Voyager team.Balance. By shining light on disagreement in the scientific community, Grant demonstrates that he knows the subject matter well. The phrase “including a few holdouts on the Voyager team” shows that he did not just go to outside researchers, but is aware of the inner workings of the team. This adds important nuance to the story and makes the reader trust Grant’s authority even more. George Gloeckler and Lennard Fisk, both from the University of Michigan in Ann Arbor, have written a paper demonstrating how plasma could become dense enough within the heliosphere to produce Gurnett’s measurement. “Gurnett definitely measured the density correctly,” Gloeckler says. “But I don’t believe you can say that what he measured is the interstellar plasma.”This quote makes clear that while Gloeckler and Fisk disagree with Gurnett, it is a question not of fact but of interpretation—and the researchers’ differing interpretations keep us engaged. Grant has folded the debate into the story, using it to build momentum, instead of centering the story on “disagreement.” This allows him to keep his focus on the specifics of the science, on the nature of evidence.

Barring a change in the magnetic field, Gloeckler believes the team should wait another two or three years for Voyager 2, which has a working instrument to measure the density and temperature of plasma, to reach a similar position in space.)) “Voyager 2 will experimentally answer this question,” he says. [highlight]“Why rush to conclusions now?”This latter part of Gloeckler’s quote is in accessible, conversational language, in keeping with the approachable tone that Grant has established.

Zank and many other astrophysicists say the evidence is overwhelming that Voyager 1 has crossed the heliopause, but they acknowledge that they have to determine why the magnetic field direction didn’t shift. At the same time, scientists are combing through more than a year’s worth of data Voyager 1 has collected since entering interstellar space. NASA estimates that Voyager 1 has enough plutonium fuel to keep all its instruments powered for another seven years, giving the probe plenty of time to measure an environment littered with particles that originated in distant stars and violent supernovas. “All this will give us considerable insight into what’s happening in the far reaches of the galaxy,” Zank says.Here, Grant zooms out from the focus on the narrow, black-and-white question of whether Voyager has exited the heliosphere and toward the potential for other insights that the spacecraft can offer in its final years.

For now, Stone and other scientists are excited about the robotic explorer’s accomplishment on August 25, 2012 — the same date, coincidentally, that the world lost its most famous human space explorer, Neil Armstrong.The first part of this final paragraph is cheery, and it also serves to remind the reader of the big picture—that no matter how scientists resolve the debate Grant has just described, the Voyager 1 mission has still achieved a great deal. Mentioning Neil Armstrong and his passing in this final phrase of the story strikes an awkward chord. It might have been better to end on the high note of the second-to-last paragraph.

You may read this story in its original format at Science News. A Q&A with writer Andrew Grant is at The Open Notebook. It was conducted by Marguerite Holloway and students in the Columbia University Graduate School of Journalism’s M.A. Science Concentration: Tryggvi Adalbjornsson, Guia Baggi, Mariana Lenharo, Maya Miller, Greta Moran, Disha Shetty, and Elizabeth Whitman.