We examine the development of the active asteroid 311P/PANSTARRS ( formerly , 2013 P5 ) in the period from 2013 September to 2014 February using high resolution images from the Hubble Space Telescope .
This multi-tailed object is characterized by a single , reddish nucleus of absolute magnitude H \geq 18.98 \pm 0.10 , corresponding to an equal-area sphere of radius \leq 200 \pm 20 m ( for assumed geometric albedo 0.29 \pm 0.09 ) .
We set an upper limit to the radii of possible companion nuclei at \sim 10 m. The nucleus ejected debris in nine discrete episodes , spread irregularly over a nine month interval , each time forming a distinct tail .
Particles in the tails range from about 10 \mu m to at least 80 mm in radius , and were ejected at speeds < 1 m s ^ { -1 } .
The ratio of the total ejected dust mass to the nucleus mass is \sim 3 \times 10 ^ { -5 } , corresponding to a global surface layer \sim 2 mm thick , or to a deeper layer covering a smaller fraction of the surface .
The observations are incompatible with an origin of the activity by impact or by the sublimation of entrapped ice .
This object appears to be shedding its regolith by rotational ( presumably YORP-driven ) instability .
Long-term fading of the photometry ( months ) is attributed to gradual dissipation of near-nucleus dust .
Photometric variations on short timescales ( < 0.7 hr ) are probably caused by fast rotation of the nucleus .
However , because of limited time coverage and dilution of the nucleus signal by near-nucleus dust , we have not been able to determine the rotation period .