For 89 years, astronomers have played a cosmic version of Where’s Waldo? Now, the game is over.
Scientists have rediscovered a near-Earth asteroid called 719 Albert, observed several times in 1911 but not seen since. Its number indicates that Albert was the 719th asteroid to have its orbit determined, a bookkeeping convention that began in 1801 with Ceres, the first asteroid identified. With Albert’s rediscovery, scientists finally know the whereabouts of all 14,788 numbered asteroids.
Johann Palisa at the Imperial Observatory in Vienna spotted Albert on Oct. 3, 1911. He and other astronomers also imaged it the following night.
Astronomers soon realized that they had unwittingly photographed the rock in several sky images made a few weeks before and a week after the discovery image. The observations revealed that the asteroid was moving swiftly across the sky, passing within 32 million kilometers of Earth—only the second asteroid then known to have come so close. Scientists also calculated that the rock, named for the Imperial Observatory’s benefactor Baron Albert Freiherr von Rothschild, orbits the sun every 4.1 years.
Despite searches over the next few decades, Albert remained at large. By 1940, astronomers had also lost track of many other numbered asteroids, but by the 1970s, they had rediscovered all but 20, notes Brian G. Marsden, director of the International Astronomical Union’s (IAU’s) Minor Planet Center at the Smithsonian Astrophysical Observatory in Cambridge, Mass.
In 1991, the center’s Associate Director Gareth V. Williams, who had begun calculating asteroid orbits while a teenager, located 878 Mildred, leaving only Albert still missing.
On May 1, Jeffrey A. Larsen of the University of Arizona in Tucson spotted an extremely faint object with the Spacewatch Telescope atop Kitt Peak, Ariz., an instrument dedicated to surveying small bodies in the solar system. From the object’s motion, Larsen deduced it was a near-Earth asteroid, and he alerted his Spacewatch colleagues Robert S. McMillan and James V. Scotti, also of the University of Arizona. They, too, imaged the object, on May 3 and May 6, confirming that it was approaching Earth.
Suspecting they had found a new asteroid, the astronomers notified the Minor Planet Center, which initially designated the body 2000 JW8. On May 9, Michael D. Hicks of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and Ronald A. Fevig of the University of Arizona observed the asteroid with another telescope on Kitt Peak.
Later that day, while compiling the information on 2000 JW8, Williams realized the object orbits the sun in the same plane as Albert. Linking the new observations with those of Albert in 1911, he found a close match. The newfound object is in fact Albert, he reports in a May 9 IAU circular. The asteroid’s orbital period is actually 4.28 years, not 4.1, a discrepancy partly responsible for Albert’s elusiveness.
At Kitt Peak, Scotti heard the news from Hicks. “We did a high-five,” says Scotti. “We had no idea we had found Albert. It is a milestone.”
Surprisingly, Spacewatch had picked up Albert at its faintest. It was then at the most distant point in its orbit, some 416 million km from Earth and about 530 million km from the sun. Barely detectable, the asteroid was less than one-millionth as bright as the faintest object visible to the naked eye on a clear night, Scotti estimates.
Researchers found Albert just in time to plan observations next year, when it will pass much closer to Earth. Coming within 43 million km of our planet on Sept. 5, 2001, the asteroid should appear much brighter. Astronomers hope that Albert, no longer an object of mystery, will give up more of its secrets, such as rotation period and size.