The vampire secret space program was too rushed to fully erase Transylvania-born rocket pioneer Hermann Oberth from the history books, but they were able to disguise their Moon-bound launches in the chaos of WWII Eastern Europe. So strong were Von Braun's oaths of silence (or so deep his fear of what had been left behind) that it took the Apollo program a handful of missions, and the sanity of more than one astronaut, before they accepted the message: the Moon was not for the living.
So, after pausing human exploration for a few decades to give themselves time to erase all evidence, NASA set their sights on Mars.
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The first human on Mars never got the chance to use the sure-to-be-historical phrase the government's memetic engineers had carefully crafted. A second before leaving the Ray Bradbury Mars lander a voice spoke on her ear, neither through her radio nor on her mind, but sideways to both, explaining that although there was no life on Mars, that didn't mean it was uninhabited. Life was just a phase, short and not particularly interesting, and she was welcome to stay on planet's terms or otherwise not at all.
The first human on Mars, whose dreams had been of red sands since her earliest memory, died of a previously unknown medical condition as she was descending the craft, reported NASA. It was never satisfactorily explained why her co-pilot did not leave the lander, and the PR fiasco put a pause on all further trips.
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When The Ones Who Condescended to Approach Suns (to use their preferred name) descended on the third planet they were already expecting the bizarre. The fourth planet had been normal enough, a common post-biological rocky planet haunted by kind and thoughtful beings, but the freakishly large moon around the third one had been occupied (tainted? The Ones Who Condescended to Approach Suns tried to keep themselves from passing judgment on such things, difficult as it was) by a group of unliving but still physical entities who spent the long nights engaged on quaint forms of astronomy, and the long days on vast underground tombs dreaming of red seas.
Yet even this anomaly did not prepare them from what they found on the planet below. That there was life on it was not on itself unheard of -- if a planet was in the right orbit biology could endure for long periods of time before the fragile chemistry of carbon had to give place to hardier forms of existence -- but the sentient beings were an entirely different, deeply unsettling matter. The Ones Who Condescended to Approach Suns, as much as they loved novelty, left the planet as soon as they could, unnerved by a superstitious but universal fear of insanity. The third planet's sentient inhabitants still believed themselves alive, and, unable to cope with reality, had retreated into fantasies of their own past, coming up with all sorts of delusions to justify why they were stuck in the compulsive repetitions of the unhappy dead, haunting mirages of long-deserted cities and sometimes individual homes.