Detection of Weather on a Young Planetary Mass Object

PSO J318.5-22 is a young free-floating planetary mass object with roughly 8.3 times the mass of Jupiter, an effective temperature of about 1160 K and a relatively young age of only 23 ± 3 million years. This planetary mass object is still glowing hot from heat acquired during its formation and it is in the process of cooling down, contracting in size as it cools. PSO J318.5-22 is a good candidate for high precision characterisation because it is free-floating, and unlike exoplanets, it is not “lost” in the glare of a host star.

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.

Reference:
Biller et al. (2015), “Variability in a Young, L/T Transition Planetary-Mass Object”, arXiv:1510.07625 [astro-ph.EP]