The Black Blight of Mars

At the colony's darkest point, they killed their brightest hope and buried her shroudless in the cold Martian soil.

Like any other nightmare, the investigation, trial, and execution were both long and feverishly rushed, everybody pretending with blank-faced desperation the outcome had not been preordained. The Mars-adapted crops had been struggling for months, putting the long-term viability of the colony at risk. And when crops fail the bones-encoded heuristic response is usually the burning of a local witch. The local witch also being the local genius bioengineer was not a factor in the deeper algebra of ritual sacrifice. There were no stakes and no mentions of the devil, but plenty otherwise would have been familiar on another planet at another time.

At first the crops did better, or so the colonists told themselves. Then the Black Blight came

What had struggled died. Fears about the long term shriveled to terror about tomorrow, and projected scarcity snarled into immediate chaos. Pleas for rescue were so stark that their Earth sponsors ran the mathematics that passed in their corporate souls for ethics and decided the expense of a rescue would be less onerous to their plans than the potential cultural trauma of a horrifying collapse.

Most colonists went back to Earth, carrying with them a few hastily grabbed samples of crops and soils, less out of scientific discipline than as symbolic coins to pay the return ferry across the Stygian orbital gap. That's how Earth scientists discovered the Black Blight was an organism, not a bioengineering failure - one brilliantly adapted to Mars, but its Earthly design clear enough in its vicious aggressiveness  to any biological cousin.

The suicide note of one of the former colonists told the Earth sponsors about the tomb. This was not made public. They just sent a research mission with spades and explosives, but by the time they sterilized the location, the blight had expanded far beyond, self-mutation engines creating millions of versions ready for whatever Earth might send.

The next, careful colony failed elegantly enough that a third attempt was deemed reasonable. When the Black Blight started killing the colonists themselves, not two in the same way, not one with dignity or without excruciating pain, they were left to die there for the safety of Earth, and Mars colonization was put on indefinite hold.