ISOPHOT detection of Pluto/Charon at 60 and 100 µ
Credit: ESA/ISO, PHT, E. Lellouch et al.
[High-Resolution image: Postscript]

Detection of Pluto/Charon at 60 and 100 micron obtained by ISOPHOT on March 17, 1997. The level of flow is approximately 0.40 Jansky at 60 micron and 0.53 Jansky at 100 micron.

Pluto along with its satellite Charon is the outermost planet of the Solar System, at a mean distance from the Sun of 5900 million kilometres. The two bodies, of similar sizes (respective diametres 2320 and 1180 km), form a unique system: they orbit around their common centre of gravity with a 6.4 day period, a time interval that also corresponds to the rotation of each body about its polar axis; therefore, Pluto and Charon permanently show the same side to each other.

This observation has been discussed in details in the ESA Science Web Note: "[ISO measures temperature variations of the surface of Pluto]".