When I was an astronomy student at Leiden Observatory in the Netherlands, pioneer asteroid hunters Ingrid van Houten-Groeneveld and her husband Kees van Houten were about to retire, after very fruitful careers. Their legacy was the discovery of over 2000 asteroids, of which some 1800 yielded orbits, in collaboration with Prof. Tom Gehrels of the Lunar and Planetary Laboratory at Tucson, Arizona. In 1960, Gehrels made a sky survey using the large 48-inch Schmidt Telescope at the famed Palomar Observatory, long before modern asteroid reconnaisances, and shipped the photographic plates to the van Houtens at Leiden Observatory. They used a large optical bench, equipped with a binocular and flip mirror, to compare each set of two large photographic plates and find the faint dots of light moving among the stars, a technique called blinking. This task is now routinely done by fast computers, or by us watching avi movies of asteroids.

In the mid-eighties, this asteroid searching was pooh-poohed by some. Why find more, if you already have thousands? Yet, among all those asteroids, Ingrid and Kees discovered two objects in peculiarly elongated orbits, 6344 P-L and 6743 P-L, on plates taken the very same nights of Sept. 24 - 28, 1960. The original designation of P-L stands for the Palomar-Leiden Asteroid Survey. 

Most asteroids move in near-circular orbits in the main asteroid belt between Mars and Jupiter, but 6344 P-L and 6743 P-L's elongated orbits bring them occasionally to within 0.05 AU from Earth's orbit. These are Potentially Hazardous Asteroids (PHA), we now know, of the type that killed off the dinosaurs. When that role of asteroids became established in the late eighties and early nineties, the search for asteroids became suddenly important insurance for our very existence. Only when an asteroid's orbit is precisely determined can we be certain it will not impact Earth in the foreseeable future.

6743 P-L, was soon recovered and has since been renamed 5011 Ptah. On the other hand, 6344 P-L remained the oldest lost Potentially Hazardous Asteroid out there. We knew it existed, it had a roughly determined orbit, but we did not know where to point the telescope.  

On the afternoon of October 3, 2007, I scanned the list of newly discovered PHA's to search for potential parent bodies of our meteor showers. In October of 2003, I found that an object called 2003 EH1 moves among the meteoroids of our most intense annual shower, the Quadrantids, and many other asteroids have been unmasked as dormant comets since. From our meteor observations, we find that these objects appear to erupt on occasion by breaking off significant chunks of matter that fall into the small dust we see on Earth as meteor showers some centuries later. The Quadrantids are suspected to have formed as recently as 1490 AD, when Chinese astronomers noticed a comet that moved in the same plane as the meteoroids.

In 1819, another such dormant comet breakup resulted in a brief comet called "Blanpain." In 2004, I found a fragment of this breakup, now called 2003 WY25, which is still moving among the meteoroids, and responsible for the December Phoenicid shower. In collaboration with Finnish astronomer Esko Lyytinen, we were able to trace an outburst of Phoenicids in 1956 to this very 1819-breakup dust.

I am sure that there are many more dormant comets out there that have not yet been identified as parent bodies of our meteoroid streams, because many streams move in low inclined orbits and their parent bodies hide among the 896 (and counting) other known PHA's. In a paper that was just accepted for publication in Icarus, I have identified 42 such candidate parent bodies, many of which need confirmation from better observations of the object and of the associated meteor shower.

So, I was content to find that newly discovered 2007 RR9 was also a possible parent body, now for an obscure shower called the gamma Piscids (#236 of the IAU shower list), which is active in mid-October and early November. 2007 RR9 had been discovered by the Catalina Sky Survey four weeks earlier on September 10. Interestingly, I already had identified a possible parent body for this shower, namely 6344 P-L, the long-lost asteroid.

When I compared the orbits of both objects, I noticed that they were very similar. So much so that they could well be the same object. I wrote Brian Marsden of the Minor Planet Center of the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, the clearing house for such identifications: "If warranted, you can probably check if this could be the same object."

The next morning, I learned the good news via an electronic circular (MPEC 2007-T13), issued by the Minor Planet Center on October 4. It was titled "6344 P-L = 2007 RR9." Instantly, the orbital accuracy for 6344 P-L improved from lousy to phenomenal, now having been observed for over 47 years, instead of only four days. Later that day, 6344 P-L was swiftly removed from the list of asteroids that could pose an immediate impact danger.

A designation as Potentially Hazardous Asteroid means that 6344 P-L is a known asteroid bigger than 150 m (500 ft) in diameter that comes to within 0.05 astronomical units of Earth's orbit (roughly 7,480,000 km or 4,650,000 miles). The size is estimated on the basis of the object's observed brightness and an assumed reflectance of 13 percent.