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What is this blue streak found on Mars?

Credits: NASA

The image captured of a sand dune on Mars shows the presence of an incredible blue colour. However, it is indeed on the red planet! So how is this possible?

The news was reported by CNN in an article published on the 27th June 2018. It refers to images captured by the Mars Renaissance Orbiter probe, a NASA space mission orbiting around Mars, that was launched in 2005. More precisely, the images were obtained using the High Resolution Imaging Science Experiment (HiRISE), a 65 kg camera on board the probe, and which is none other than the “most powerful camera ever sent to another planet”. 

One image in particular attracted attention, as it shows a blue coloured sand dune. In reality, the dune is not blue, but grey, which can be explained. Contrary to rovers, orbiters don’t touch the ground, and they survey the planet from an area outside its atmosphere. The camera captures many details, but despite its power, it cannot see everything clearly, due to the abundance of dust. (However, without this camera, the human eye would see only the equivalent of a grey mist.)

This is why three photos were taken of the same area, and adjusted individually with red, blue and green filters, via infrared. When the contrast was introduced into this mysterious photo, the dune appeared blue because it is made of a finer material and/or has a different composition from the environment in which it finds itself, according to Alfred McEwen, director of the Planetary Image Research Laboratory in the University of Arizona (US).

Thus, there is no big mystery about the red planet, but this new information can teach us a little more about how the HiRISE camera works, and the way in which the images are treated.

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