X Marks the Spot

Credit: NASA/JPL/University of Arizona

“X” marks the spot in this image of wind-blown dunes in Argyre Plani­tia from NASA’s HiRISE camera.

Explore the hills and dune fields of this plain within the huge Argyre impact basin. What shapes and sto­ries does your imag­i­na­tion cre­ate? Share your sto­ries below. Wind, sand and dust play a huge role in shap­ing the sur­face in the Mar­t­ian high­lands. Broad expanses of sand dunes, dri­ven by pre­vail­ing winds blow­ing in a north­west­erly direc­tion, dom­i­nate the shal­low val­leys in this image. These types of sand dunes are called trans­verse dunes. They are dri­ven by con­stant winds blow­ing con­sis­tently from a cer­tain direc­tion. The most promi­nent fea­ture in this image is the “X” along the large dune in the mid­dle of the image. This dune is a bit dif­fer­ent than oth­ers in the image. It is long and nar­row, flow­ing with the direc­tion of the wind. Sci­en­tists call these lon­gi­tu­di­nal dunes.

The “X” and other dark marks espe­cially near the top of the image show the paths of dust dev­ils. Dust dev­ils occur on Earth too. These strong, well-formed whirl­winds are like mini-tornadoes. They are ver­ti­cally rotat­ing columns of air formed when warm air at the sur­face punches through cooler air above. The col­umn of air may begin to rotate. When it does, more warm air is sucked in from the sur­round­ing area giv­ing it more power. The sur­round­ing cooler air con­tains the spin­ning col­umn of warm. On Mars, spin­ning dust dev­ils pick up the fine dust leav­ing darker sand behind show­ing the swirling paths. Sand and dust also fill in craters and other shal­low areas through­out this image.

Argyre Plani­tia is a plain located within the huge impact basin in the south­ern high­lands of Mars. The basin is about 1,120 miles across (1,800 km) and is believed to be the sec­ond largest impact basin on Mars. The cen­ter of Argyre drops 3.2 miles (5.2 km) below the sur­round­ing plains. The basin is vis­i­ble from Earth and was first mapped by Gio­vanni Schi­a­par­elli in 1877. He named the fea­ture after the myth­i­cal island of sil­ver in Greek mythology.