New Insights into Mars's Polar Geology: A Study of the Basal Unit (BU) in Planum Boreum

 

Figure 1 - (a) Mappa di elevazione MOLA di Planum Boreum con posizioni geografiche annotate. (b) Mappa di elevazione MOLA e SHARAD combinata dell'unità basale (BU) e delle pianure circostanti ottenuta in questo studio. La mappatura della riflessione superficiale della BU nei profili SHARAD attraverso Planum Boreum ci ha permesso di integrare la topografia delle porzioni esposte della BU misurate da MOLA per creare questa mappa. Il reticolo in entrambi i pannelli ha passi di 1° di latitudine e passi di 30° di longitudine. (c) Rappresentazione schematica delle relazioni stratigrafiche tra le unità geologiche di Planum Boreum, modificata da Tanaka et al. (2008).

This article is a summary of this scientific publication: Nerozzi, Stefano, Maya R. Ortiz, and John W. Holt. "The north polar basal unit of Mars: An Amazonian record of surface processes and climate events." Icarus 373 (2022): 114716.

This scientific study focuses on the basal unit (BU), a significant geological formation located within the Planum Boreum region of Mars. Situated in the planet's north polar region, the BU holds valuable insights into Mars's surface processes and climatic shifts that occurred during the Amazonian Period, spanning the last three billion years.

The study uses data collected by the Shallow Radar (SHARAD) instrument aboard the Mars Reconnaissance Orbiter (MRO), along with high-resolution imagery from HiRISE and CTX cameras, to examine the BU's structure, composition, and evolution.

The BU comprises two distinct subunits: the rupēs unit and the cavi unit. The rupēs unit, older and situated beneath the cavi unit, consists of layered deposits of water ice and fine-grained rock particles. Scientists believe the rupēs unit formed through vertical accumulation of windblown dust and ice particles. This unit exhibits evidence of past erosion, resulting in the formation of characteristic scarps and mesas.

The cavi unit, younger and overlaying the rupēs unit, is composed of layers of windblown sand and ice. Its composition indicates that the cavi unit formed during cyclical periods of ice deposition during colder epochs interspersed with sand accumulation during warmer periods.

Through meticulous analysis of radar profiles and imagery, researchers have revised the understanding of the BU's size. They have determined that the BU covers a larger area than previously thought, with the cavi unit being particularly more extensive. This discovery emphasizes the crucial role of wind-driven processes in shaping the Martian polar landscape over an extended period.

The study also sheds light on the age of the BU and its subunits. By examining the distribution of impact craters on exposed surfaces, scientists have estimated the age of the rupēs unit to be between the Late Hesperian and Early Amazonian periods, approximately 2.1 to 2.9 billion years old. The cavi unit, younger than the rupēs unit, likely started forming in the Middle to Late Amazonian period and continued accumulating until recent times, potentially even in the present day.

One of the study's key findings is the identification of a previously undetected lobe of the cavi unit. This discovery adds a significant volume to the BU and extends its reach further than previously mapped. The presence of this lobe highlights the dynamic nature of Martian polar geology and the substantial influence of aeolian processes on the region's evolution.

Another remarkable observation is the presence of a large, roughly circular depression in the cavi unit, interpreted as an impact crater. This crater, estimated to be 15-20 km in diameter, provides evidence of a significant impact event that affected the Martian north polar region. The presence of this crater emphasizes the role of impact cratering in shaping the Martian landscape.

By combining radar data with high-resolution imagery, researchers were able to reconstruct a detailed chronological evolution of the BU. This reconstruction outlines the formation of the rupēs unit, a period of erosion, the subsequent deposition of the cavi unit, and ongoing surface modifications driven by wind, ice, and impacts.

The study raises several intriguing questions that require further investigation. Researchers are eager to understand the precise composition of the rupēs unit, the source of its materials, and the factors contributing to the transition from the rupēs unit's formation to the cavi unit's accumulation. Understanding these aspects will provide valuable insights into the interplay of geological and climatic forces that shaped the Martian polar regions.

The study highlights the importance of combining different types of remote sensing data to investigate Martian geology. By integrating radar profiles with high-resolution imagery, researchers were able to gain a more comprehensive understanding of the BU's structure, composition, and evolution. This approach can be applied to other regions on Mars to unravel their geological history and gain further insights into the planet's past.

The findings of this study contribute significantly to our understanding of Martian polar geology and the planet's overall evolution. The BU stands as a testament to the dynamic nature of Mars's surface and the interplay of various geological processes over billions of years. Future research endeavors will undoubtedly uncover further secrets hidden within this fascinating geological formation.