This image provided by NASA and taken from NASA's Curiosity rover shows what appear to be blue rocks on the Martian surface. The rocks appear blue as a result of a filter that makes the surface appear as it would under Earth’s sunlight. (NASA/JPL-Caltech/MSSS)

The latest images from the Mars Curiosity rover and the HiRise camera aboard the Mars Reconnaissance orbiter have left some Earthlings scratching their heads and wondering: What are those blue rocks?

Well, according to NASA, they’re not blue so much as gray. In a photo released yesterday taken by HiRise, the dunes between Curiosity and Mount Sharp are shown as dark blue waves, appearing like an ocean bed on the more tan martian surface.

But why change the colors?

The answer has to do with sunlight, and the fact that daylight on Earth is, of course, different from daylight on Mars. In order to compensate, images from Curiosity are put through a filter that makes the images appear as if they were taken in Earth’s daylight. The filtering process is called “white balancing.” It’s useful for geologists who, as Earthlings, are accustomed to observing rock formations under Earth’s sunlight. Here, for example, is the image above without the “white balancing” filter:


And here’s another, showing a close-up of a rock formation near the rover that was exposed during the landing:

An area excavated by the blast of the Mars Science Laboratory’s descent stage rocket engines. (NASA/JPL-Caltech/MSSS)

And now, without the filter:

The filter isn’t absolutely necessary, as the Atlantic’s Alexis Madrigal writes, but it is certainly helpful. And, of course, it’s pretty cool to see Mars through Earth-colored lenses.

It’s worth noting that Madrigal’s take is well worth a read, particularly his observation on “the contingency of our own visual systems.”

But before you head over there, here are the dunes mentioned earlier.

This color-enhanced view — taken by the High Resolution Imaging Science Experiment (HiRise) on NASA's Mars Reconnaissance Orbiter as the satellite flew overhead — shows the terrain around the rover's landing site within Gale Crater on Mars. Colors were enhanced to bring out subtle differences, showing that the landing region is not as colorful as regions to the south, closer to Mount Sharp, where Curiosity will eventually explore. In reality, the blues are more gray. (NASA/JPL-Caltech/University of Arizona )

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