How to fix this punctuation

[wendyroo]

My 9 year old wrote the following sentence about Einstein:

In one of his most famous thought experiments there were two twins, one traveled in a rocket at almost the speed of light to a star four light years away, while his brother stayed on earth, when he got back he had only aged eight years, but his brother had aged 29 years.

That is actually two or three sentences run together, right?

My first thought was to change it to something like,  "In one of his most famous thought experiments there were two twins, one who traveled in a rocket at almost the speed of light to a star four light years away and his brother who stayed on earth.  When the space traveling brother got back he had only aged eight years, but his brother on Earth had aged 29 years."

But I'm trying to follow Andrew Pudewa's advice to correct a child's writing as little as possible to make it grammatically "legal".  Is there a less intrusive way to fix the run-on while also leaving the construction fundamentally the same?

Thanks.

[forty-two]

In one of his most famous thought experiments there were two twins.  One traveled in a rocket at almost the speed of light to a star four light years away, while his brother stayed on earth.  When he got back he had only aged eight years, but his brother on Earth had aged 29 years.

This is the most unobtrusive way to fix it I can think of: breaking up the sentence into three sentences, and adding in "on Earth" for clarity.

[Storygirl]

10 minutes ago, forty-two said:

In one of his most famous thought experiments there were two twins.  One traveled in a rocket at almost the speed of light to a star four light years away, while his brother stayed on earth.  When he got back he had only aged eight years, but his brother on Earth had aged 29 years.

This is the most unobtrusive way to fix it I can think of: breaking up the sentence into three sentences, and adding in "on Earth" for clarity.

I agree.

[RootAnn]

1 hour ago, forty-two said:

In one of his most famous thought experiments, there were two twins.  One traveled in a rocket at almost the speed of light to a star four light years away, while his brother stayed on earth.  When he got back, he had only aged eight years, but his brother had aged 29 years.

I agree with this but added a comma after experiments in the first sentence and after "he got back" in the last sentence. And, I don't think the "on earth" part is necessary as it is clear he only has one brother.

So, only some commas, periods, and capitalization needed!

[KrissiK]

20 hours ago, forty-two said:

In one of his most famous thought experiments there were two twins.  One traveled in a rocket at almost the speed of light to a star four light years away, while his brother stayed on earth.  When he got back he had only aged eight years, but his brother on Earth had aged 29 years.

This is the most unobtrusive way to fix it I can think of: breaking up the sentence into three sentences, and adding in "on Earth" for clarity.

I agree with this fix.