MARSIS

MARSIS. The Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) is a low-frequency, pulse-limited radar sounder and altimeter. It is a primary scientific instrument aboard the European Space Agency's Mars Express orbiter, designed to probe the Martian surface and subsurface to depths of several kilometers. Its primary objectives are to search for evidence of subsurface water in the form of ice or liquid reservoirs and to study the structure of the planet's ionosphere.

Overview

Developed through a collaboration between the Italian Space Agency and NASA's Jet Propulsion Laboratory, MARSIS represents a landmark in planetary remote sensing. The instrument operates by emitting low-frequency radio pulses between 1.3 and 5.5 MHz, which penetrate the Martian crust and are reflected back by subsurface layers with differing electrical properties. This technique, analogous to ground-penetrating radar used on Earth, allows scientists to create detailed cross-sectional images of the subsurface. The data from MARSIS has fundamentally altered our understanding of Mars's aqueous history and current cryosphere.

Instrument Design and Operation

The instrument consists of a main electronics assembly and a unique 40-meter long dipole antenna, deployed in two 20-meter fiberglass booms, complemented by a 7-meter monopole antenna oriented perpendicularly. This configuration allows MARSIS to operate in different modes: subsurface sounding, active ionospheric sounding, and altimetry. For subsurface investigation, it uses frequency bands centered at 1.8, 3.0, 4.0, and 5.0 MHz, with lower frequencies providing greater penetration at the cost of resolution. The radar pulses are transmitted and the returning echoes are analyzed to determine the time delay and strength, revealing the depth and nature of reflecting interfaces. Operations are carefully planned around the orbit of Mars Express to optimize coverage of key regions like the south polar layered deposits.

Scientific Discoveries

MARSIS has produced a series of groundbreaking discoveries since it began operations. Its most significant finding was the detection of a persistent, bright subsurface radar reflector approximately 1.5 km below the surface of the south polar cap, interpreted as evidence for a stable body of liquid water, likely a subglacial lake laden with perchlorate salts. The instrument has also mapped vast deposits of nearly pure water ice buried beneath the Medusae Fossae region and within the Utopia Planitia basin. Furthermore, its data has been crucial for characterizing the layered composition of the polar layered deposits, revealing climate cycles recorded in the ice, and for estimating the global properties of the Martian ionosphere and its interaction with the solar wind.

Mission History and Deployment

MARSIS was launched from the Baikonur Cosmodrome aboard a Soyuz-FG rocket with a Fregat upper stage on 2 June 2003, as part of the Mars Express mission. The deployment of its long antenna booms, initially delayed due to concerns about potential damage to the spacecraft, was successfully completed on 4 May 2005 after extensive simulations at the European Space Operations Centre. The instrument began its nominal science operations in July 2005. The mission, initially planned for one Martian year, has been repeatedly extended due to its exceptional scientific return, with MARSIS continuing to operate and collect data well into the 2020s, far exceeding its design lifetime.

Technical Specifications

The instrument has a mass of approximately 12.6 kg. It requires an average power of about 60 watts during active sounding operations. The dipole antenna is 40 meters tip-to-tip, and the monopole is 7 meters long. The radar transmitter operates with a peak output power of 10 watts. It achieves a range resolution of about 150 meters in free space (improved to tens of meters in subsurface processing) and can penetrate to theoretical depths of up to 5 kilometers in icy regions, depending on the material's conductivity. Data is processed on-board and transmitted to Earth via the spacecraft's high-gain antenna for further analysis by teams at the University of Rome Tor Vergata and other partner institutions.

Category:Spacecraft instruments Category:Mars Express Category:Radar