18 Apr. 2011

 

2011 GP59, a blinking asteroid

 

On the night between the 8th and 9th of April this year, a near-Earth asteroid was discovered at the Observatorio Astronomico de Mallorca in Andalucia, Spain. Preliminary calculations determined that it would have reached a minimum distance of 533,000 km, (1.4 times the mean Earth-Moon distance) on 15th April at 19:09 UTC.
All in all nothing exceptional, given that objects have passed closer and been larger. Nonetheless, the new asteroid, 2011 GP59, with a diameter of 50 metres, would still cause quite some damage were it to enter the Earth's atmosphere.
The strange thing about this asteroid is its shape, the 50 metres in fact refers to its length rather than its "diameter", as its other axes must be much smaller. This conclusion has been reached because during its close passage the light reflected from the object was seen to blink on and off, as well demonstrated in several videos made by both professional an amateur astronomers; see for example: www.youtube.com/watch?v=O7wsAZNr56E.
According to Don Yeomans, a world expert on minor solar system bodies and manager of NASA's Near-Earth Object Program Office (at Jet Propulsion Laboratory in Pasadena, California), better known as "Spaceguard", the elongated shape of 2011 GP59 and its rotational period of about 7.5 minutes, explain why the asteroid is seen to disappear every 4 minutes or so. When oriented so that the minimum surface area reflects sunlight towards us the object dims significantly.
A projection of the orbit of 2011 GP59 into the future indicates that this Near-Earth Object does not represent a threat to Earth.

 

by Michele Ferrara & Marcel Clemens

credit: Near-Earth Object Program Office/JPL