The discovery data. The spectrum of carbon monoxide around Pluto is shaded in red. The surrounding signals are random "noise". The brightness of the signal (on the vertical axis) is given in units of degrees that are equivalent to a temperature of the source. This is much less than the 50° above absolute zero (50 Kelvin) estimated for the atmosphere, because Pluto fills only a tiny fraction of the sky-area seen by the telescope.
J.S. Greaves/Joint Astronomy Center