Acidalia Planitia

The plain is named after a corresponding albedo feature on a map by Giovanni Schiaparelli, which was in turn named after the mythological fountain of Acidalia. Some places in Acidalia Planitia show cones, which some researchers have suggested are mud volcanoes. The scientific community is divided over whether an ancient ocean existed on the plain and other parts of the northern lowlands.

Geological history

There are several hypotheses regarding the geological history of Acidalia Planitia based on evidence from satellite data.

Springs and steam vents

Acidalia Planitia was once covered by ancient crust. Its surface eroded into knobs of iron/magnesium phyllosilicates during the Amazonian. Sediments filled the empty plain, leaving the phyllosilicate knobs as protrusions through the surface. The spatial density of these knobs is consistent with the ancient crust that was once above Acidalia Planitia.

Hydrated silica materials surround the phyllosilicate knobs and the sides of rocky slopes. Rather than covering the entire surface, these features are localized. This indicates that the plain was once home to springs and steam vents not extensive bodies of water such as oceans or glaciers.

Oceans

Utopia Planitia is a similar plain at the same latitude as Acidalia Planitia. Etched flows in its terrain suggest that mud flowed into Utopia Planitia creating a large reservoir of water and mud in the deepest part of the basin, about 1000 km across. This may have been the remnants of a more extensive ocean that covered all of the northern lowlands including Acidalia Planitia. The Vastitas Borealis Formation (VBF) stretched across both Utopia and Acidalia Planitiae and delineated the threshold for an ancient ocean. The two segments of the VBF at Utopia and Acidalia have congruent ages, reliefs, crater frequencies, albedos, thermal properties, and superpositions of geological features. This suggests that the Acidalia Planitia may have once been covered by a large Martian ocean.

Glaciers

Craters on Acidalia Planitia are asymmetrical. Mars Orbital Laser Altimeter (MOLA) data revealed that the slopes of the pole-facing crater walls are shallower than the equator-facing slopes. Other studies show the opposite asymmetry to be true. The two theories indicate either biased glacial deposition during the Amazonian era or long-term creep of hundreds of meters of ice-rich regolith beneath the surface, respectively.