A 211-year-old mystery has finally been solved by an astronomy historian, who's identified the person responsible for naming those rocky objects orbiting between Mars and Jupiter.
The first years of the 19th century were glorious ones for astronomy. In 1800 William Herschel, already famous for spotting Uranus in 1781, found that the Sun emits infrared energy. The next year Johann Ritter followed with the discovery of ultraviolet light.
Meanwhile, Europe's scientific circles were abuzz about the realization that not one but two planet-like objects were orbiting the Sun between Mars and Jupiter. Astronomers had suspected as much — after all, the numerical orbit spacings produced by the Titius-Bode Law had predicted that a planet should be lurking there.
In fact, a dozen astronomers, handpicked by Baron Franz Xaver von Zach and nicknamed the "Celestial Police," were readying to search for this undiscovered world when, on January 1, 1801, Giuseppe Piazzi spotted the long-sought interloper using a small refractor atop the royal palace in Palermo, Italy. At first, Piazzi thought he'd found a comet, but it later proved to be Ceres. A second body in that same region, Pallas was found on March 28, 1802.
But neither was truly a planet. Herschel used a special projection system to estimate that Ceres was only 162 miles (260 km) across and Pallas just 147 miles (237 km).
So what were they? Herschel has long been credited with coining the term asteroids, derived from a Greek word meaning "starlike," because he introduced the term at a meeting of London's Royal Society in May 1802 and later published it in the Society's Philosophical Transactions.
But according to astronomy historian Clifford Cunningham (National Astronomical Research Institute of Thailand), "Asteroid was Herschel's choice, but it was not his creation." Documents found by Cunningham in Yale's Beinecke Rare Book and Manuscript Library show that credit instead goes to a little-known Greek specialist named Charles Burney Jr.
As Cunningham learned, Herschel was casting about for a suitable name for the new bodies and had reached out to Dr. Charles Burney Sr, a close friend and colleague. Burney in turn quickly wrote to his son, who at the time was one of England's preeminent Greek scholars. The correspondence between them shows that the father had proffered suggestions like stellula (the diminutive of stella) before concluding, "It must not be a big name for so small a star."
The son's reply didn't turn up during Cunningham's research. What did, however, was a later letter from the senior Burney to Frances Crewe, discussing Herschel's just-published report about Ceres and Pallas in Philosophical Transactions. "They are not allowed by Herschel to be either Planets or Comets," Burney writes, "but asteroids, italick, a kind of star — a name [which] my son, the Grecian, furnished."
Herschel chose asteroid over other contenders (such as planetkin, planeret, and planetling), but he wasn't thrilled with it. At one point he asked his close friend Sir Joseph Banks, then president of the Society, to come up with a better word. Banks, in turn, contacted Stephen Weston, who came up with the word aorate. "Herschel rejected this as well," Cunningham explains, "accepting asteroid as the best of a bad lot of ideas."
One problem is that Herschel's colleagues still thought of Ceres and Pallas as planets, so a new moniker simply wasn't needed. "The abuse heaped on Herschel for introducing the word asteroid was unparalleled in the history of astronomy," Cunningham says. "It was not just a rejection — it was outrage, ridicule and contempt." Only Wilhelm Olbers, who'd found Pallas, embraced Herschel's choice. Piazzi preferred planetoid, but by then Herschel's Royal Society paper had been published.
"It has taken me 30 years of research into Herschel and the asteroids to uncover this," notes Cunningham. (You can follow some of that quest in his 2001 book, The First Asteroid.) Cunningham presented his findings three weeks ago at a meeting of the American Astronomical Society's Division for Planetary Sciences.
Meanwhile, come February 2015 we'll know whether planetoid would have been the better choice. That's when NASA's Dawn spacecraft finally reaches Ceres (actually about 600 miles across) and begins several months of intense scrutiny of the asteroid belt's largest member.