Isidis Planitia is a plain located inside a giant impact basin on Mars, centered at ; Isidis Planitia is partly in the Syrtis Major quadrangle and partly in the Amenthes quadrangle. It is the third biggest obvious impact structure on the planet after the Hellas and Argyrebasins – it is about in diameter. Isidis was likely the last major basin to be formed on Mars, having formed approximately 3.9 billion years ago during the Noachian Period. Due to dust coverage, it typically appears bright in telescopic views, and was mapped as a classical albedo feature, Isidis Regio, visible by telescope in the pre-spacecraft era. A study reported in Icarus described the complex geologic history of parts of Isidis, especially areas near the Deuteronilus contact. This contact is the supposed edge of a vast Martian ocean. The researchers found evidence of a Late Hesperian/Early Amazonian Sea in the area. The sea would have quickly frozen over. Eskers formed under the ice. Just to the west of Isidis is Syrtis Major Planum, a low-relief shield volcano that is a prominent dark albedo feature of Mars, which formed after the basin. The westernmost extent s bounded by a subregion, Northeast Syrtis with diverse geology. Around the Isidis basin magnesium carbonate was found by MRO. This mineral indicates that water was present and that it was not acidic, pH conditions more favorable for the evolution of life. The name "Isidis Planitia" follows the earlier name Isidis Regio. Isis is the Egyptian goddess of heaven and fertility.
The Beagle 2 lander was about to land in the eastern part of Isidis Planitia in December 2003, when contact with the craft was lost. In January 2015, NASA reported the Beagle 2 had been found on the surface in Isidis Planitia. High-resolution images captured by the Mars Reconnaissance Orbiter identified the lost probe, which appears to be intact.
In 2018 the Jezero_ in the north west rim of the Isidis basin was selected as a landing site for the Mars 2020 mission, including the Perseverance rover.
