There is a small but importantly not insignificant chance that Mars once hosted microbial life, or still does today. For that reason, there are certain areas of the Red Planet that may be off limits to future explorers, robotic or human. These are the Special Regions.
Once thought to be cold and lifeless, Mars now looks like it could have been habitable. If we want to find out in the future, though, we'll need to make sure we don't contaminate it with Earth microbes. Thankfully, most of Mars is deadly to Earth life, but there could be some regions where microbes hitching a ride on a spacecraft could lead to a false detection of Mars life in the future.
Thus, scientists drew up the idea of Special Regions. As defined by the Committee on Space Research (COSPAR) in their 2008 Planetary Protection Policy, there are regions “within which terrestrial organisms are likely to propagate or a region that is interpreted to have a high potential for the existence of extant martian life forms.”
In 2016, this definition was updated slightly to be more specific. A Special Region now is one that has a water activity rating of 0.5 to 1. Water activity is a measure of how suitable it is for life, dependent on how easily life could use it for food.
The other main feature of a Special Region is that it has a temperature warm enough to support terrestrial organisms. This is defined as being -25°C (-13°F) and higher. There has also been a recommendation to include methane in the definition, which may support biological life, but that has not yet been included.
Here’s the kicker, though. We haven’t found a single Special Region on Mars yet. Zip. Nada.
“There are no Special Regions identified on Mars today,” John Rummel from the East Carolina University, the lead author on the paper that redefined Special Regions, told IFLSLcience. “We’ve defined them, but we haven’t found them.”
So what’s the issue? Well, while we haven’t found any such regions yet, we may well do in the future. And if we do, that could pose some problems.