I read this in the mid-'90s; the book was from my father's collection and was showing its age. The main characters had to leave Earth for some reason, and wouldn't be pursued because of Earth attitudes toward space travel (or maybe atomic energy). They ended up visiting a lot of the planets, or their moons (in the case of the gas giants) and on each planet met some sort of weird alien.

Early on, one alien that was what we'd now call a xenomorph taught them telepathy (which teaching caused a headache); one of the worlds had a nuisance vermin (rabbit equivalent) that could become invisible and make other things invisible by having enough of them sitting between the viewer and the object; one world the aliens were centaur-like; one world built their civilization with almost no metal, and the main characters escaped imprisonment by convincing their jailers to provide them with materials that (unknown to them) would embrittle the walls so that they would crumble at a kick; and there were other fantastic portrayals of that sort.

I don't remember the author's name, except that I remembered seeing it as a not-an-author.

I'm fairly sure it was one side of an Ace Double, but I have no recollection of the 'flip'.

  • When you say "not-an-author" do you mean it was a name you recognized for some reason other than being an author (like, say, Carl Sagan) or it was just a no-name author you'd never heard of?
    – DavidW
    Jan 7, 2022 at 20:16
  • 1
    The first - I recognized the name, but the context that I recognized the name from was not that he was an author. Jan 7, 2022 at 20:18
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    What about the early alien would lead us to call it a xenomorph? Can you give us details of the description given that leads to that comparison?
    – Harabeck
    Jan 7, 2022 at 20:19
  • I just remember that the main characters had problems on that world because the aliens were shape-changers. Jan 7, 2022 at 20:20
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    And here is a link to a question about one of the stories scifi.stackexchange.com/questions/231436/… Jan 18, 2022 at 6:11

1 Answer 1


Rewritten as requested.

Sounds like the Penton and Blake stories by John Campbell, better known as "The Planeteers".

The eponymous characters are a duo of grifters who live a few adventures in the solar system: there are centaurs, telepathy, shapeshifting aliens and everything else you might remember.

A few themes from Tv Tropes

A blog post

These stories, collected, were published as an Ace Double with "The Ultimate Weapon", also by Campbell, which instead has one Aarn Munro as the protagonist but shares some of the same themes as the Planeteers'. There are a few more Aarn Munro stories if you might be interested.

Isfdb page on the issue

Another blog post

  • This was definitely it; I found my copy (actually, my dad's copy that I inherited). The "flip" was The Ultimate Weapon rather than The Mightiest Machine, but I haven't read it yet to determine whether it's the "same" story. Jan 11, 2022 at 18:31
  • My fault! You know, sometimes you think one thing and write another: that happened to me when I wrote the flip side title. Anyhow, I've corrected it based on your correction! Glad you find what you were looking for!
    – Zab Zonk
    Jan 11, 2022 at 22:52
  • Nitpick: "Ultimate Weapon" isn't an Aarn Munro story, though it's very similar. Jan 18, 2022 at 16:19

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