Methane Ice

Explanation: Photographs of condensed methane in a 1.5-cm test cell in a laboratory ice facility at Northern Arizona University. The temperature in the cell on the left is about 91 K (-182 degrees Celsius, -296 degrees Fahrenheit), with methane gas on top, liquid in the middle, and methane ice on the bottom. The image on the right shows the methane in the test cell completely frozen, at about 80 K (which looks no different from Pluto's temperature of about 40 K). At this spatial scale, methane looks perfectly clear to the human eye, but a much thicker slab would look blue, because there are some very weak absorption bands at the red end of the wavelength range of human vision.

Pluto

Image credit: Will Grundy.