"Internal heat can be produced in several ways:
*From the sun. But Pluto is too far away (about 6 billion km) to receive any significant heat from the sun.
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Pluto compared to the size of the United States |
*From tidal heating due to interaction with its largest moon, Charon. This may play some role in generating the internal heat of, for example, Jupiter’s moon, Io. But Jupiter is massive—over 1 million times more massive than Charon. Even though Charon is closer to Pluto than Io is to Jupiter, the tidal forces are still about 100 times smaller. That is, way too small to play a significant part.
*From internal heat present at its formation. This seems the only remaining possibility.
And that is where the dilemma is for long-agers. If Pluto were 4.5 billion years old, its internal heat would have vanished billions of years ago."
CMI