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Martian Diaries

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Where to Draw the Lines? A Mapping Project
By Jeffrey Marlow

As Curiosity hurtles toward its landing site at Gale Crater, the Entry, Descent, and Landing team has taken center stage. But once the roving begins, Curiosity will come face to face with the rocks and soil that, hopefully, will tell the story of Gale Crater's watery past.

With the impending surface operations phase in mind, the science team has used the eerie calm before the storm to take a closer look at the landing site terrain. It has been an exercise in scientist crowd-sourcing, as Mars Science Laboratory Project Scientist John Grotzinger tasked the Mapping Working Group with developing a detailed map of the final landing ellipse.

Context of Curiosity Landing Site in Gale Crater, with Ellipse
This oblique, southward-looking view of Gale crater shows the landing site and the mound of layered rocks that NASA's Mars Science Laboratory will investigate.

Localization scientists Tim Parker and Fred Calef solicited input from over 30 members of the science team. The instructions went something like this: take a 2.25 square kilometer region, study every last grainy pixel until you go cross-eyed, and categorize the distinct units. Surface units that look different from orbit - with smoother surfaces, more fracture lines, or more craters, for example - likely point to different geological processes that may warrant follow-up investigation by Curiosity's on-board instruments.

It fell to Calef and a dedicated mapping team to bring the pieces together, an unenviable exercise in cat-herding and computerized cartography. For hours, the group debated: "Does it make sense to draw the line here or not?" says Calef by way of an example. "Does it make sense to connect these units or keep them separate?"

Now, Calef and Mars Science Laboratory science team members Lauren Edgar, Abigail Fraeman, and Katie Stack are synthesizing the results, doing battle with the powerful but somewhat unwieldy mapping program. The changes in surface features are gradual, and "there's no right answer of where exactly to draw the lines, which is part of the reason it's so hard," notes Fraeman.

The resulting high-resolution unit map is endlessly debatable, but it's also an important product that will influence Curiosity's roving plans in the coming days. "These maps will be used to help guide the drives directly," says Grotzinger. Understanding where geologically distinct patches are located can help the rover sample a greater diversity of environments and contextualize its measurements, making for a more efficient first few weeks on the Martian surface.