ESA - Light and dark in the Phoenix Lake

Phoenicis Lacus has an area of 8100 sq km (59.5 x 136 km), which corresponds to the size of Corsica.

This image was obtained on 31 July 2010 using the High-Resolution Stereo Camera (HRSC) on ESA’s Mars Express spacecraft.

Credits: ESA/DLR/FU Berlin (G. Neukum)

They say you can’t judge a book by its cover but, with planets, first impressions do count. New images show where complex fault lines in Mars’ Phoenicis Lacus region have resulted in terrain with a distinctly contrasting appearance.

Nineteenth-century astronomers were the first to see Phoenicis Lacus on Mars. They identified it as a dark spot, and thought that it resembled a sea.

Now we know that it is not a body of water but the southwestern extension of the complex Noctis Labyrinthus system, which stretches away from the giant volcanoes of Mars’s Tharsis region.

The brightness of a surface feature is still the first thing planetary astronomers notice. It is known as the albedo and is partly determined by the composition of the surface material.

For example, ice is more reflective than rock. The texture of the surface also plays a part, with rough surfaces reflecting less sunlight and so appearing darker than smooth surfaces. 

On 31 July 2010 the High-Resolution Stereo Camera (HRSC) on the ESA spacecraft Mars Express obtained images of Phoenicis Lacus at approximately 13°S/249°E. 

The data were acquired during orbit 8417 with a ground resolution of approximately 17 m per pixel.

Credits: NASA MGS MOLA Science Team

Phoenicis Lacus was formed by the uplift of the Tharsis volcanic plateau. 

The continual episodes of strong volcanic activity in Tharsis not only lifted the plateau, but also deformed Phoenicis Lacus, creating uplifted blocks and multiple fault lines at different orientations.

A prominent collapse feature in Phoenicis Lacus sinks to a depth of about 3 km below the surrounding terrain. 

This image was created using a Digital Terrain Model (DTM) obtained from the High-Resolution Stereo Camera on ESA’s Mars Express spacecraft. 

Elevation data from the DTM are colour-coded: purple indicates the lowest-lying regions, and grey the highest elevations. The scale is in metres.

Credits: ESA/DLR/FU Berlin (G. Neukum)

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