  P/2011 S1 (Gibbs) is an outer solar system comet or active Centaur with a
similar orbit to that of the famous 29P/Schwassmann-Wachmann 1. P/2011 S1
(Gibbs) has been observed by the Pan-STARRS 1 (PS1) sky survey from 2010 to
2012. The resulting data allow us to perform multi-color studies of the nucleus
and coma of the comet. Analysis of PS1 images reveals that P/2011 S1 (Gibbs)
has a small nucleus $< 4$ km radius, with colors $g_{P1}-r_{P1} = 0.5 \pm
0.02$, $r_{P1}-i_{P1} = 0.12 \pm 0.02$ and $i_{P1}-z_{P1} = 0.46 \pm 0.03$. The
comet remained active from 2010 to 2012, with a model-dependent mass-loss rate
of $\sim100$ kg s$^{-1}$. The mass-loss rate per unit surface area of P/2011 S1
(Gibbs) is as high as that of 29P/Schwassmann-Wachmann 1, making it one of the
most active Centaurs. The mass-loss rate also varies with time from $\sim 40$
kg s$^{-1}$ to 150 kg s$^{-1}$. Due to its rather circular orbit, we propose
that P/2011 S1 (Gibbs) has 29P/Schwassmann-Wachmann 1-like outbursts that
control the outgassing rate. The results indicate that it may have a similar
surface composition to that of 29P/Schwassmann-Wachmann 1.
  Our numerical simulations show that the future orbital evolution of P/2011 S1
(Gibbs) is more similar to that of the main population of Centaurs than to that
of 29P/Schwassmann-Wachmann 1. The results also demonstrate that P/2011 S1
(Gibbs) is dynamically unstable and can only remain near its current orbit for
roughly a thousand years.
