Some symmetry - the last flows as easily as the first, even in its original version. It's in perfect Italian sonnet form.

So my editing was largely just increasing alliteration, one of my favourite tools, and adding an internal rhyme. Replacing "bathed" with "soaked" and "reigns" for "cloaks" (lines 3 & 4) does double duty - it rhymes in an odd place in those lines, while adding an pleasing set of sounds in the phrase "blackness cloaks" - the click of the "c"s and the "k"s, the sibilant "S" sounds that end both words, the "l"s in both words that each into "eternally"(technically "called the “alveolar lateral approximant,” which means that you put your tongue against your upper teeth and push the air around the sides of your mouth.) The matched rhyming line 8 also has a plethora of related sound words "bleak darkness leaves bright". All this comes from paying more attention to my original words. 

And then I put it up on AllPoetry, and rethought my changes. Some I sent back to the original, as they seemed to be better after a rethink than the first changes, and others I had left looked slightly tired. Who knows - I may re-edit again in 10 years time. 

To me this is the work of a poet. A master carpenter will not leave a splintered, unfinished piece. They will carve and plane and sand and varnish a piece of wood, so a utilitarian piece of furniture becomes an objet d'art. I was happy with the original, as someone who had written for 3-4 years while working and living. Coming back 40+ years back, I have learned to use my tools better, I hope.

Poor old Pluto - it was only discovered in 1930, and was originally thought to be about the same size as Mercury. When they discovered its moon Charon, they could actually get a better idea of its size and mass (considerably smaller), so in 2006, at the age of 74, it was downgraded to "dwarf planet" - as if Micky's dog had wandered into the story of Snow White.

Originally, I thought the frozen sea I put on Pluto would never exist, or if it did, might be frozen methane or similar. As it turns out, there may indeed be a liquid water ocean underneath a deep frozen surface. Lucky guess! As for the feeble light of earth, you would never see it without a significant telescope.