Wikipedia
Baltisk Crater is a crater in the Argyre quadrangle of Mars. It is located at 42.7° South and 54.7° West, is 52 km in diameter, and was named after a town in Russia.
Impact craters generally have a rim with ejecta around them, in contrast volcanic craters usually do not have a rim or ejecta deposits. As craters get larger (greater than 10 km in diameter) they usually have a central peak. The peak is caused by a rebound of the crater floor following the impact.
Image:Wikibaltisk.jpg|Baltisk Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter). Dark areas are dunes. Fans are visible in the lower right. Image:Wikibaltiskdunes.jpg|Dunes in Baltisk Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter). Note: this is an enlargement of a previous image. Image:Wikibaltiskfan.jpg|Fans in Baltisk Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter). Note: this is an enlargement of a previous image. Arrows point to layered parts of the fans.
Many craters once contained lakes. Because some crater floors show deltas, we know that water had to be present for some time. Dozens of deltas have been spotted on Mars. Deltas form when sediment is washed in from a stream entering a quiet body of water. It takes a bit of time to form a delta, so the presence of a delta is exciting; it means water was there for a time, maybe for many years. Primitive organisms may have developed in such lakes; hence, some craters may be prime targets for the search for evidence of life on the Red Planet.