ESA has released new images captured by its Mars Express space probe’s High Resolution Stereo Camera (HRSC) showing Nirgal Vallis on the planet Mars. It’s a river valley that extends for over 700 kilometers, so vast that it crosses the Coprates and Margaritifer Sinus quadrangles. A few billion years ago, when the rivers were filled with liquid water, they probably filled Holden Crater, making it a lake with a diameter of about 150 kilometers and a depth of up to about 250 meters.