How NASA defines "Special Regions" for Mars missions

Here’s something interesting I came across last year while writing the article “How NASA decides where to land on Mars”. NASA had some restrictions in place for selecting the region its Perseverance rover will land on and explore. From its landing site selection page:

The Mars 2020 Science Definition Team (SDT) report concluded that the primary mission objective of exploring an ancient environment does not require the mission to access Special Regions. A Special Region is defined as a location where the temperature could exceed -28° Celsius and water activity is at least 0.5. Water is key to life as we know it, and water activity considers the availability of water and water vapor as a potential support for life processes. The Mars 2020 mission is restricted from landing in, entering, or creating, a Special Region on Mars.

The Mars 2020 mission relies on engineering systems that are based on NASA’s Mars Science Laboratory mission, and these engineering systems do not readily support sterilization requirements that apply to missions accessing Special Regions.

The Mars 2020 mission carries a radioisotope thermoelectric generator, which naturally produces heat. The heat produced could raise temperatures, melt ice, and provide an environment where microbial life could reproduce. Thus, the Mars 2020 mission is also restricted from landing in sites where scientists suspect water, brine, or water ice could be present, or could be induced, within 5 meters (about 16.4 feet) of the surface. In the event of an unsuccessful landing, engineers estimate that an impacting spacecraft would not go below a 5-meter depth.

I get why planetary protection demands such a restriction but for a flagship mission specifically being sent to determine “Are we alone?”, this landing site criteria could very well prevent Perseverance from addressing that question.

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