Long-lost ‘Potentially Hazardous Asteroid' re-located

Washington, Oct 5 : Astronomers have found that the recently discovered Earth threatening asteroid 2007 RR9 is in fact the long lost object 6344 P-L observed nearly half a century ago.

Astronomers at the Minor Planet Center of the Smithsonian Astrophysical Observatory in Cambridge, MA have confirmed work by SETI Institute astronomer Peter Jenniskens that the recently discovered asteroid 2007 RR9 is in fact the long lost 6344 P-L.

The object was last seen in 1960, and ever since has had the peculiar distinction of being the only Potentially Hazardous Asteroid (PHA) without a formal designation.

“The object was long recognized to be dangerous, but we didn’t know where it was. Now it is no longer just out there,” said Jenniskens.

A designation as Potentially Hazardous means that 2007 RR9 is one of the 886, and not 887 known asteroids bigger than 150 m (500 ft) in diameter, which come 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.

Jenniskens said the object might not be even an asteroid.

“This is a now-dormant comet nucleus, a fragment of a bigger object that, after breaking up in the not-so-distant past, may have caused the gamma Piscid shower of slow meteors (IAU #236) that is active in mid-October and early November,” Jenniskens said.

“2007 RR9 moves in a 4.70-year orbit, nearly all the way out to the distance of Jupiter, and because of this elongated orbit, it has a Tisserand parameter of T = 2.94, which defines it dynamically as a Jupiter Family Comet (T = 2.0 - 3.0), not an asteroid (T > 3.0).

“So far, this object has not yet been seen to be even weakly active, but the now dormant comet is still moving closer to the Sun. It is sliding rapidly toward visibility in the southern hemisphere, and is expected to brighten to magnitude +18.5 in mid-October,” he said.

Gareth V. Williams of the Minor Planet Center said 2007 RR9 would pass Earth around November 6 at 0.07 AU, when the minor planet is at high latitudes in southern skies.

The original designation of P-L stands for “Palomar-Leiden,” the juxtaposition of two observatory names that reflect what was a very fruitful collaboration by the trio of pioneer asteroid searchers Tom Gehrels of the University of Arizona, and Ingrid van Houten-Groeneveld and her husband Cornelis Johannes van Houten of the Netherlands.

Gehrels made a sky survey using the 48-inch Schmidt Telescope at the famed Palomar Observatory, long before modern asteroid reconnaissance, and shipped the photographic plates to the van Houtens at Leiden Observatory in the Netherlands.

There, Ingrid discovered 6344 P-L on four plates taken on September 24-28, 1960.

The trio are jointly credited with several thousand asteroid discoveries, but only 6344 P-L is potentially dangerous to Earth. (ANI)




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