Sad but true: the Phoenix Mars Lander officially died on Monday as mission planners stopped listening for a heartbeat. Phoenix has been silent for about a week now as dust accumulation and waning hours of daylight conspired to starve the Lander’s solar panels of light. But as project manager Barry Goldstein said yesterday, the team is “declaring an end to mission operations at this point.”

That said, the mission was, if not Earth-shattering, certainly a success. Its 5-month lifespan was 2 months longer than scheduled (though usually target timeframes are low-balled in order to lower expectations), and our knowledge of the planet’s geochemistry deepened with several important finds. With Mars exploration, it seems that the more we know, the more we know we don’t know. Pre-Mars Exploration Rovers, scientists had assumed that the planet had ancient oceans and lots of carbon dioxide, leading to the deposition of carbonates, which on Earth are particularly good at preserving evidence of life.

Chemical evidence from Opportunity turned all of this upside-down. The rover extrapolated a very acidic water chemistry that would have precluded carbonate precipitation. Around the same time, hyperspectral orbiters started finding sulfate deposits that tended to confirm the high-acidity, carbonate-free interpretation of Mars’ watery past.

And then came Phoenix. While the most flashy discovery was its detection of water ice, more unexpected data came from soil analysis: not only was the soil more alkaline than the MERs had led us to believe, but Phoenix also detected calcium carbonate – the first encounter with the long-awaited carbonate deposits of Mars.

And so, the plot thickens. Perhaps the most important take-away is that Mars was and is a complicated place. Just like on Earth, different places at different times produce very different conditions: we now see that it was quite possible to have acidic water producing sulfates at one location and more alkaline water precipitating carbonates elsewhere. To me, this is encouraging as we delve deeper into the search for life. If one potentially habitable micro-environment comes up empty, there are probably several other very different niches to examine.

Meanwhile, the Mars Exploration Rovers live on…