Observations of PSO J318.5-22 in the infrared reveal the presence of variability in its luminosity. The first observation was on 9 October 2014 in the J band (1.1 to 1.4 μm) over 5 hours and a variability of 10 ± 1.3 percent was measured. The second observation was on 9 November 2014 in the J band and a variability of 7 ± 1 percent was measured. The third observation was on 11 November 2014 in the K band (2.0 to 2.4 μm) and a variability of up to 3 percent was measured.
Although variability is common for cool brown dwarfs, this is the first time variability has been observed for such a planetary mass object. The most likely cause for the variability is inhomogeneous cloud cover on PSO J318.5-22, which makes this the first detection of weather on a free-floating planetary mass object. The observed variability also indicates that PSO J318.5-22 is a fast rotator, with a rotation period of several hours.
Biller et al. (2015), “Variability in a Young, L/T Transition Planetary-Mass Object”, arXiv:1510.07625 [astro-ph.EP]