From a blot post from Remanzacco Observatory:
This minor planet, belonging to the "Apollo" class, is also flagged as a "Potentially Hazardous Asteroid", an object that, because of its orbital parameters, might represent a possible threat of impact for planet Earth (http://neo.jpl.nasa.gov/neo/
It has beeen discovered serendipitously by the Spanish amateur astronomer J. M. Bosch Santa Maria de Montmagastrell, MPC#B74 on 2009, Sept. 16.2, ay magnitude about 17. At that time it was posted on the NEO-CP webpage of the Minor Planet Center as "jmbo11"; after a couple of days it was withdrawn, because it was not confirmed by any further observations.
On 2009, Sept. 22, the LINEAR sky survey picked-up a fast moving object, that was posted in the NEO-Cp as "BQ24981". After some follow-up observations from various sites, on 2009 Sept. 23 the MPC published M.P.E.C. 2009-S72 (http://tinyurl.com/yer5xmr), informing that the two objects mentioned before were actually the same celestial body.
We performed some follow-up of this object on 2009, Sept.23.1, remotely from the Mayhill Station (NM) of the GRAS network. You can see our image here:
According to the NEODyS webpage this object. about 0.5-Km in diameter, made a close pass to Earth on 1980, Oct. 4, at a minimum possible distance of about 0.009 AU (nominal distance of about 0.04 AU).
Congratulations to J. M. Bosch for his find.
E. Guido, G. Sostero, P. Camilleri, M. Jaeger, E. Prosperi, W. Vollmann
Link: Remanzacco Observatory Blog Post on 2009 ST19
From an article in the Barcelona Reporter:
After six days of monitoring by the Minor Planet Centre at the University of Harvard, it has been termed, asteroid 2009 ST19.
Lieida professor spots large asteroid over 1 kilometre in diameter, 645,000 miles from Earth.
Professor Josep Maria Bosc from the Field Learning Observation Centre of the Universe, discovered the asteroid on September 16 from his observatory, on Montmagastrell Santa Maria (Lleida) , which in real terms means the asteroid came the closest to Earth than any other in the past.
After six days of monitoring by the Minor Planet Centre at the University of Harvard, it has been termed, asteroid 2009 ST19. This is classed as an Apollo, a potentially dangerous kind to the planet because its orbit overlaps with that of Earth. The asteroid is also the largest, at more than a kilometre in diameter, that has come close to Earth. At the time of its closest approach it passed 645,000 miles abve the Earth.
The last similar incident dates back to 1937, when the asteroid Hermes passed 750,000 miles over the Earth.
Link: Barcelona Reporter Article
Link: Minor Planet Center Circular for 2009 ST19