Elysium Planitia is a vast, flat plain in Mars’s eastern hemisphere, a region of considerable scientific interest. It is the second-largest volcanic region on the planet, surpassed only by the Tharsis region. Its unique geological characteristics and potential for past or present water activity make it a compelling subject for planetary exploration.
Geological Landscape
Elysium Planitia is a volcanic province with extensive lava flows that smoothed its terrain. This region hosts three shield volcanoes: Elysium Mons, Hecates Tholus, and Albor Tholus. Elysium Mons, the largest, rises approximately 13 kilometers above the surrounding plains and has a summit caldera around 14.1 kilometers in diameter.
Hecates Tholus, about 160 by 175 kilometers, features an 11.3 by 9.1-kilometer caldera complex. Albor Tholus is about 160 by 150 kilometers with a 35 by 30-kilometer summit caldera, its flanks partially covered by lava from Elysium Mons. These volcanoes and their surrounding plains, composed of basaltic lava, reflect a long history of volcanic activity shaping the Martian surface.
Evidence of Water and Ice
The landscape of Elysium Planitia reveals evidence of past water activity and buried ice. A series of long fissures known as Cerberus Fossae are thought to have released large volumes of underground water. This outflow carved the Athabasca Valles, one of Mars’s youngest river valleys, demonstrating fluvial processes.
Further observations suggest a large frozen sea may lie beneath the dusty surface of the plain, similar in size and depth to Earth’s North Sea. This frozen body, roughly 800 by 900 kilometers and 45 meters deep, would be protected by volcanic ash. Plate-like features from Mars Express resemble pack ice, supporting the idea of a buried ice reservoir.
The InSight Mission’s Landing Site
Elysium Planitia was chosen as the landing site for NASA’s InSight mission, which stands for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport. Its primary objective was to study Mars’s deep interior, not its surface features. This required a landing site with specific conditions for instrument deployment.
Its flat, stable, and relatively rock-free terrain made it ideal for InSight’s seismometer and heat flow probe. Engineers needed a low elevation for atmospheric braking and a near-equator location for consistent solar power. Elysium Planitia offered the “perfectly boring” environment needed for geophysical investigations of the planet’s internal structure.
Key Discoveries from InSight
The InSight mission provided significant insights into Mars’s interior. It detected “marsquakes,” recording over 1,300 seismic events. Data from these marsquakes allowed scientists to map the planet’s internal layers, the first direct seismic exploration of another terrestrial planet’s interior.
Mars’s crust beneath the landing site is thinner than anticipated, measuring 25 to 40 kilometers thick, and comprises three distinct layers. InSight’s observations revealed Mars possesses a surprisingly large, liquid iron core with a radius of about 1,800 kilometers. This core is less dense than previously modeled, indicating a mixture of lighter elements with molten iron.