Herschel.s first observation of a potentially hazardous object: 2005 YU55

We propose to observe the Apollo and Ctype asteroid 2005 YU55, which is on a MarsEarthVenus crossing orbit, during its upcoming exceptional Earth approach. In November 2011 it will pass within 0.85 lunar distances (0.85 LD) of the Earth, during which it will have a brief (less than one OD) observing window for Herschel. No asteroid of that size has ever been observed to pass inside 1 LD (and it will not happen again before 2028) although, according to recent orbit simulations, it does not pose any risk of an impact with Earth for the next 100 years.The proposed 0.3 hours of HerschelPACS observations will allow us to characterize the object.s size and its albedo. In combination with the foreseen radar measurements we will also be able to derive thermal surface properties which are strongly influencing nongravitational forces, considered as one of the reasons for the large uncertainties in longterm orbit studies. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]