Chasing New Horizons: Inside the Epic First Mission to Pluto

Alan Stern and David Grinspoon. Picador, 2018. 295 pages. $28.00.

Shortlisted for the 2019 ΦBK Science Award

By Jay M. Pasachoff

One of the most astounding events in the history of the space program was the close flyby of Pluto and its moons by NASA’s New Horizons spacecraft on July 14, 2015. The incredible story of how this tremendous success was rescued from near disaster, and how the project even got started in the face of many doubters, is well told in this book.

Alan Stern, of the Southwest Research Institute in Boulder, Colorado, is the hero of the story, and we largely read the results of Stern’s dictating chapters to planetary astronomer and popular author David Grinspoon—though the chapters, we read, then went through many backs-and-forths between the two authors. Though written in the third person, we see Stern’s authoritative recollections and interpretations. Stern is the one who pushed through 6 mission concepts over 13 years to get New Horizons approved as “the first mission to the last planet.”

I was interested to see how young Alan Stern, at age 13, was inspired by an issue of National Geographic Magazine, with Saturn on the cover, to go into planetary exploration (though I wonder if he forgot, skipped over, or was partly inspired by my own article about my total solar eclipse expedition later in the issue.)

Reading this book during the next few months would put you in good shape to understand and rejoice in the next step for New Horizons: its flyby of a small object even farther out in the solar system than Pluto. On January 1, 2019, the spacecraft will fly by 2014 MU69, recently nicknamed Ultima Thule after a traditional name for an unreachable object far out in the north. I was fortunate to be one of about 60 scientists sent by NASA to Argentina and South Africa last year, with 24 new medium-sized portable telescopes and electronic detectors, to try to pinpoint the position of this further object. As a result of our efforts, New Horizons was even swerved slightly a few months ago to send it only 2000 miles above the surface of this 30-mile-across object that may, indeed, be a pair of objects in a close orbit or even stuck together.

In the book’s prologue, and then in more detail near the end, we readers hold our collective breath as we learn of the spacecraft’s apparent shutdown only days before its arrival at Pluto after a nine-year flight. Though the onboard computer ultimately restarted—it had merely been overloaded—we get a feeling for the dedication of Stern and of hundreds of others who had to accomplish major tasks in less time than previously thought possible, even getting the final mission sequences uploaded over again to the restarted computer—at that time so far away that the return travel time for a signal sent up was over 8 hours (compared with the Earth-Sun distance of only eight light-minutes). As the authors quote from a World War I phrase, the nine-year voyage was “months of boredom punctuated by moments of terror.”

The first half of the book, pre-2006-launch, describes the background of the mission, and how many tries Stern, especially, had made to move Pluto onto the front burner of NASA funding and mission selection. I chaired a session on the history of the Pluto mission at last year’s meeting of the American Astronomical Society’s Planetary Sciences Division, and it is wonderful to have so much of the history discussed in such an authoritative fashion.

One section of the book describes the International Astronomical Union’s reclassification—I call it a promotion—of Pluto to be the first to be discovered in a belt of over 1000 similar objects out beyond Neptune. As the book describes, only 4 percent of the membership of the IAU was still present for the voting on the last day of the two-week IAU General Assembly, and Stern ably speaks for the continued planethood of Pluto, with its surface details, its atmosphere, and its moons. (I myself was present, so I know that some details on the drafting of and voting for the new classification in the book under review weren’t quite as it happened, such as how the dynamical astronomers caused a last-minute change in the definition of a “dwarf planet,” which is Pluto’s current classification.) I was glad to learn that Stern chose that name in analogy to astronomers’ use of “dwarf star” for the most common type of star, including our Sun, though many people in the general public don’t realize the high-quality ranking of the term.

I remember clearly how exciting it was to be at Johns Hopkins University’s Applied Physics Laboratory in Laurel, Maryland, when the spacecraft flew by Pluto (we cheered a local countdown), though the spacecraft was over four light-hours away, meaning a signal took over four hours to reach us, and for the flyby the spacecraft was turned to take crucial close-up data rather than have its antenna pointed at Earth. From the earlier part of the book, we had read about the compromises and choices that had had to be made in order to get the mission approved within the strict financial caps that NASA required.

Near the book’s end, we get an excellent description of the feeling of the scientists involved as the images and other data came in—though we appreciated the nervousness that had led to a fail-safe set of images to be transmitted the day before, in case New Horizons died at closest approach by hitting a dust particle or other debris orbiting Pluto. A bonus is an extra list at the end of 10 major discoveries about Pluto and its largest moon, Charon, with paragraphs of explanation.

The book’s two color sections, each consisting of eight double-sided pages, begin by containing images of key mission personnel and, at the end of the second section, include an excellent selection of fantastic images sent back by New Horizons as it flew through the Pluto/Charon system.

I have my hotel reservations for attending the receipt of images from Ultima Thule. New Year’s Day should bring fantastic pictures of the farthest object ever to be imaged close up, and the worldwide coverage we expect (the Pluto flyby was on front pages all over the world) should excite us all. Alan Stern’s and David Grinspoon’s interesting Chasing New Horizons is preparing us for the best possible understanding of what will be going on, and will heighten our enthusiasm.

Astronomer and author Jay M. Pasachoff is the director of the Hopkins Observatory and Field Memorial Professor of Astronomy at Williams College. He is a Visitor in the Carnegie Observatories. Williams College is home to the Gamma of Massachusetts Chapter of Phi Beta Kappa.