M.P.E.C. 2012-Q72, issued on 2012 Aug. 28, reports the discovery of the PHA asteroid 2012 QG42 (discovery magnitude 16.8) by Catalina Sky Survey on images taken on August 26.3 with a 0.68-m Schmidt + CCD.
2012 QG42 has an estimated size of 200 m - 500 m (H=20.4) and it will have a close approach with Earth at about 7.43 LD (Lunar Distances) or 0.019 AU at 0510 UT on 14 Sept. 2012. This asteroid will reach an average magnitude of 13.6 around September 10-12. 2012 QG42 is a current radar target for ground based radio telescopes. Astronomers at Goldstone and Arecibo will try to observe it on September as "this object should be a really strong delay-Doppler imaging target".
It was classified as a PHA ((Potentially Hazardous Asteroid). PHA are asteroids larger than approximately 100m that can come closer to Earth than 0.05 AU. None of the known PHAs is on a collision course with our planet, although astronomers are finding new ones all the time.
We performed some follow-up measurements of this object, remotely from the Siding Spring-Faulkes Telescope South on 2012, September 04.5, through a 2.0-m f/10.0 Ritchey-Chretien + CCD. Below you can see our image, stack of 4x10-second exposures, taken with the asteroid at magnitude ~15.2 and moving at 4.35"/min. At the moment of the close approach on 14 September, 2012 QG42 will move at ~ 49"/min.
Below you can see a short animation showing the movement of 2012 QG42 (each frame is a 10-second exposure). Click on the thumbnail for a bigger version:
UPDATE - September 14, 2012
On mpml mailing list, Brian Warner presented the first lightcurve obtained using data provided by different amateur astronomers all around the world:
"Critter is still observable but the phase angle is now around 70° whereas most of the data are from < 20°. The amplitude and shape of the curve may be evolving and so it becomes more and more difficult to merge all the data into a single set. Ideally, a data set taken over the next 24 hours from stations widely-separated in longitude would be treated as "stand alone" and would help with modeling - LOTS!"
Below you can see the plot of the current photometry for 2012 QG42. It reveals this PHA rotates once every 24.278 hours, or 24 hours, 16 minutes, 40.8 seconds. (click on the image for a bigger version).
In the meantime the radar team announced on mpml mailing list that radar echoes from 2012 QG42 have been successfully detected at Goldstone on September 13:
"We spent most of our time during the track improving the orbit by estimating Doppler and ranging corrections to the ephemerides. The radar data are consistent with a slow rotation period as inferred from the lightcurves reported by Brian Warner. We have one more track scheduled at Goldstone on Sep. 15 and four tracks at Arecibo on Sep. 14-17."
by Ernesto Guido, Nick Howes & Giovanni Sostero