A ground-penetrating radar instrument that NASA helped develop for the European Space Agency's Mars Express orbiter has completed a five-month campaign of observing subsurface layering in the north polar ice cap of Mars. The campaign is a highlight of the orbiter's extended mission. The Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) made observations from altitudes as low as about 233 miles (375 kilometers) during several hundred passes over the pole. The MARSIS team is analyzing the data and plans to publish findings. For more information, see http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=49771 .