Regarding the universe; life, death, neutrons, stars; everything

Question

My brother Yzarc recently returned from his summer road trip, so I went to visit him.
He seemed unusually quiet, sitting pensive in a chair and watching the clouds. This was unusual, since typically he is rambling and trying to be clever. I asked if he was still suffering from his recent injury. He said no, he was just thinking.
"About what?" I asked.
"You know, the universe; life, death, neutrons, stars; everything," he replied.
"And what are your thoughts?"
"Well, there's a lot I could say..."
I looked at my watch. "Maybe you sum it up in one word?"
Yzarc gave me a long, thoughtful look, and answered:
"Nature's jaunty, purer music ruptures man, returns heaven."
"Beautiful. But that's not one word," I said.
"I haven't gotten there yet," he said. "The word is on this piece of paper."
I switched the paper to my side of the table and inspected it. It read:
'SsARrMRrrrVRrrEeeMESU'
"But that's-".
I was about to say 'But that's not a real word', when I realized it was just him trying to be clever. Which meant my brother was back to his old self, which in the end, made me happy.
What was Yzarc's single thought regarding the universe? How did you know?

Note: Like all of my puzzles, the solution will be simple* and self-evident - once it is solved. No specialized knowledge or tricky computer searches required (in fact discouraged).

*simple as in 'can be explained to a third grader', not simple as in so obvious that it is not a puzzle. I hope you know what I mean.

Hint:

Step one is to unscramble the 8 word anagram. There are a few clues scattered throughout the story as to its result.

Answer 1

The answer is that Yzarc thinks that the universe is:

UNFATHOMABLE

As pointed out in the Hint, the first step to solving this puzzle is to 'unscramble the 8 word anagram'. The 8 words in question are 'Nature's jaunty, purer music ruptures man, returns heaven' and these anagram to:

MERCURY, VENUS, EARTH, MARS, JUPITER, SATURN, URANUS, NEPTUNE (i.e. the names of the 8 planets of The Solar System)

This solve came about indirectly by noticing that many of the letters in Yzarc's second message are the starting letters of the planets, and then spotting the other clues scattered about. Most notably the title's connotations to space, and Yzarc's "watching the clouds". This hunch then proved correct when working it out!

Next, turn our attention to the ciphertext: SsARrMRrrrVRrrEeeMESU. The way we need to interpret this is firstly to...

...split it up into runs of the same letter:

Ss A Rr M Rrrr V Rrr Eee M E S U

Each of these represents a single letter of the alphabet in the final message. How? Well...

Write out the letters of the alphabet in order. Then write out the names of the planets in a single line directly beneath it (in fact, we need only write out the first 26 letters of this concatenated string):

ABCDEFGHIJKLMNOPQRSTUVWXYZ
MERCURYVENUSEARTHMARSJUPIT

What we have here is a key! Now we need to translate...

...each run of the same character of length n as implying we should find the n^th occurrence of this character in the planet string, and then replace it with the letter of the alphabet to which it corresponds in the key.

For instance, 'Ss' (n=2) means the second instance of the letter 'S' in the string. This is the 'S' at the end of 'MARS' (the first is at the end of 'VENUS') and corresponds to the letter 'U'. Next, 'A' (n=1) means the first occurrence of the letter 'A' in the string, which is the 'A' in 'EARTH' and corresponds to 'N'.

This looks promising, and it is likely then that by continuing this process we will produce a 12-letter word beginning with 'UN...'. See it through to completion and the final answer is:

UNFATHOMABLE!