Argyre Planitia

Argyre Planitia is a plain located in the Argyre impact basin in the southern highlands of Mars. Its name comes from a map produced by Giovanni Schiaparelli in 1877; it refers to Argyre, a mythical island of silver in Greek mythology.

Argyre is centered at 49°42′S 316°00′E / 49.7°S 316.0°E / -49.7; 316.0 and lies between 35° and 61° S and 27° and 62° W. The basin is approximately 1,800 km (1,100 mi) wide, believed to be the second-largest impact basin on Mars after Hellas Planitia, and drops 5.2 km (17,000 ft) below the surrounding plains.

The basin was possibly formed by a giant impact during the Late Heavy Bombardment of the early Solar System, approximately 3.9 billion years ago, and may be one of the best preserved ancient impact basins from that period. Argyre is surrounded by rugged massifs which form concentric and radial patterns around the basin. Several mountain ranges are present, including Charitum and Nereidum Montes.

Four large Noachian epoch channels lie radial to the basin. Three of these channels (Surius Valles, Dzígai Valles, and Palacopas Valles) flowed into Argyre from the south and east through the rim mountains. The fourth, Uzboi Vallis, appears to have flowed out from the basin's north rim to the Chryse region and may have drained a lake of melting ice within the basin. A smaller outflow channel named Nia Valles is relatively fresh-looking, and probably formed during the early Amazonian after the major fluvial and lacustrine episodes had finished.

The original basin floor is buried with friable, partially deflated layered material that may be lake sediment. No inner rings are visible; however, isolated massifs within the basin may be remnants of an inner ring.

The crater Galle, located on the east rim of Argyre at 51°S 31°W / 51°S 31°W / -51; -31, strongly resembles a smiley face.