Comparison of WASP-121b Stratosphere with Brown Dwarf Atmosphere

This diagram presents evidence for the existence of a stratosphere on a planet orbiting another star. As on Earth, the stratosphere increases in temperature with altitude. The water emissions from the Jupiter-sized planet's upper atmosphere show this. The results are in marked contrast to the spectrum of a failed star, a brown dwarf, which shows water absorption because the atmosphere is cooling with altitude increase.