March 31, 2007 | David F. Coppedge

The Hot Moon Epidemic Spreads to the Suburbs

A planetary symptom we might call “Enceladus fever” is apparently an epidemic.  Now, we’ve found that it infects some of the Kuiper Belt Objects (KBOs) beyond the orbit of Neptune.  More and more small bodies are being found with internal heat that has broken out onto the surface.  This is a big surprise.  Small bodies should have frozen solid in billions of years.
    Richard Kerr reported for Science today about discussions at the Lunar and Planetary Sciences conference held March 12-16 in Texas.1  Here’s the surprise in a nutshell:

What would erupting volcanoes, even icy ones, be doing on the coldest bodies in the solar system?  Temperatures hover around 50 kelvin [-370° F] on Kuiper belt objects (KBOs), which circle on the frigid dark fringes of the solar system for eons on end.  But astronomers recently have seen signs that fresh ice has formed on KBOs in the geologically recent past.  Now, researchers have calculated how a KBO, at least a larger one, might husband its primordial allotment of heat until the present day….
    Somehow, relatively warm crystalline ice has formed of late on the largest KBOs, but scientists have had trouble explaining where the necessary heat came from.  KBOs have been cooling inside for billions of years, and unlike satellites such as Io or Enceladus, they do not orbit a huge planet that can spare a trickle of tidal energy to heat the smaller body’s interior.

Scientists committed to the consensus age of the solar system (4.5 billion years) cannot endure any thought of revising that number down, so the challenge is to model how a small body could retain its primordial heat for 4.5 billion years.  Here’s the explanation in brief.  If the body began with enough fast-burning radioactive fuel, like potassium-40, it might get hot enough inside to differentiate into layers.  A molten core would form, surrounded by an insulating rocky shell.  A liquid ocean might form above the rock layer.  As ice expands, it might crack, propagating channels to the surface.  If there is ammonia in the mix, it might lower the melting point to permit slurries of ammonia-water “magma” to spread on the surface.
    Nevertheless, a veteran planetary scientist commented, “I’m surprised it stays so hot.”  If this phenomenon is common to KBOs, maybe one of the largest – the Pluto-Charon system – could be observed up close in 2015 when the New Horizons spacecraft pays a visit.


1Richard A. Kerr, “Cold, Cold Bodies, Warm Hearts,” Science, 30 March 2007: Vol. 315. no. 5820, p. 1789, DOI: 10.1126/science.315.5820.1789a.

The moyboys* of the Lyell Theater seem to be on the defensive these days.  The planets and moons are not following the script.  It’s supposed to be Act MMMMDVI of King Liar but they’re playing as if it’s Act CCM of a different play.  Is this a super condensed version of the show, or are we in the wrong playhouse?  The audience of the little hamlet stirs.  This is not just much ado about nothing; it’s becoming a tempest, or, as you like it, Lyell’s labors lost.  Measure for measure, all’s well that ends well, but this is looking more like a comedy of errors.  If the moyboys in desperation start singing For he’s a jolly othello,” the audience may just get up and walk out.  The timing of the crew couldn’t be worse.  Across the street, there’s a blockbuster oratorio drawing in huge crowds: The Creation.
*Believers in “millions of years, billions of years.”

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Categories: Solar System

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