Hacker News Reader

1) it would be a visceral demonstration of the fragility of life on Earth

2) overnight, it would shift our estimate of the likelihood of life forming into "terrifyingly likely". Terrifying, because if life forms on any planet even roughly like Earth, the idea of aliens showing up one day and killing us all is suddenly horribly plausible.

Although, life on Mars could have a common origin with life on earth. There are after all meteorites on Earth that are believed to be of Martian origin. If microbes from Mars seeded Earth or vice versa, then finding life in both places doesn't mean the odds of it arising are higher than we thought.

Dreadful, if you take the Dark Forest theory to heart (see Liu Cixin's second book in the Three Body Problem trilogy).

In any case, what I said stands for the relatively more likely scenario of "signs of past life now gone"

One "dreadful"consequence could be quarantine lest we violate the prime directive