system
Given the following post, respond as if you're commenting on Reddit:
human
[John Carter of Mars] What's going on in 2019?

Is there still life on Mars today? Green Martians, Red Martians, etc? Evidence of their society? 

If so, Earth must know about them by now. How is that going?
gpt
A running theme of the John Carter books is that Mars is a dying world. In the first story (iirc) Carter saves Mars from loosing its atmosphere by sacrificing himself to repair the atmosphere factory. While Burroughs wrote plenty more books in the series after that, it is reasonable to assume that eventually Carter eventually failed to save Martian life from annihilation, resulting in a total extinction event that rendered the planet a cold, barren desert like it is today.

Sandstorms came to covert the lost cities of Martian civilization in the century following life's extinction, leaving the planet appearing, from orbit, to be nothing more than a lifeless rock. Our probes failed to land in the right spots, or dig deep enough, to uncover the planet's history. However, once humanity puts its boots on Mars and gets digging, her secret history and the adventures of one Earthling will come to light once more.