I found SPACE PONIES on an asteroid called Spahr??? on a the "Fire and Ice" medium map "AFTER" I had wiped out all  3 of the other AI players on Hard and was just trying to use up extra credits in preparation for beating the Pirate Base to test out something for myself.  I am relatively new at this and had beaten all of the small maps and had just been working through the mediums one at a time.  This was AFTER it said I won and gave me the option to keep playing.  When I finally quit the game and looked up what it was exacty online, I went back to check achievements and it is not there....Sooooo, it may be something you may have to find during normal play while there are still other players in the game before you win.  At least that's my observation so far and possibly the reason why some people aren't finding it as an achievement.  As far as I know, it gives no bonus to speak of except halving the cooldown time of all anti-matter weapons including the novalith cannon...uh yeah, I wish!!!   It does nothing I am aware of but did manage to beat the pirates on my second attempt.

--If you look for Space Ponies AFTER you win a map by searching every available planet, it MAY not register as an achievement even if you find it!!!

Side note:  the reason I decided to "time" destroying the pirate base was to see if doing so would eliminate/"make disappear" the roaming pirate raiders attacking me elsewhere.  It doesn't and they kept attacking me elsewehere, so I would assume the same would be true if playing AI during the game--sic the pirates on someone else then wipe out the pirate base and the pirates will still attack the intended enemy AI player!!!

P.S.  I have managed to paralyze a roaming pirate raid when I managed to destroy the enemy AI planet they were going to attack before they even phased towards it...I was kinda hoping they would redirect towards another closeby planet that was just as close and only one phase jump away, but they just waited a few minutes and headed home....that SUCKED, but was a learning experience.  I suppose as soon as the raid is announced, the pirates are "dedicated" towards their target and if it no longer exists, they give up, stand around motionless for a few minutes and return home