A new study using data from the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) instrument on ESA’s Mars Express spacecraft has found clear signs of the Martian atmosphere acting as a single system, with processes occurring at low and mid levels significantly affecting those seen higher up. The findings appear in the Journal of Geophysical Research: Planets.
Mosaic of the Valles Marineris hemisphere of Mars projected into point perspective, a view similar to that which one would see from a spacecraft. The distance is 1,550 miles (2,500 km) from the surface of the planet. The mosaic is composed of 102 Viking Orbiter images of Mars. The center of the scene shows the entire Valles Marineris canyon system, over 1,240 miles (2,000 km) long and up to 5 miles (8 km) deep, extending form Noctis Labyrinthus, the arcuate system of graben to the west, to the chaotic terrain to the east. Many huge ancient river channels begin from the chaotic terrain from north-central canyons and run north. The three Tharsis volcanoes (dark red spots), each about 15.5 miles (25 km) high, are visible to the west. South of Valles Marineris is very ancient terrain covered by many impact craters. Image credit: NASA / JPL-Caltech.
Understanding the atmosphere of Mars is a key topic in planetary science, from its current status to its past history.
The Martian atmosphere continuously leaks out to space, and is a crucial factor in the planet’s past, present, and future habitability — or lack of it.
The planet has lost the majority of its once much denser and wetter atmosphere, causing it to evolve into the dry, arid world we see today.
However, the tenuous atmosphere Mars has retained remains complex, and scientists are working to understand if and how the processes within it are connected over space and time.
The new study, led by University of Leicester researcher Beatriz Sánchez-Cano, now offers clear evidence of a sought-after link between the upper and lower atmospheres of the planet.
“The lower and middle levels of Mars’ atmosphere appear to be coupled to the upper levels: there’s a clear link between them throughout the Martian year,” Dr. Sánchez-Cano said.
“We found this link by tracking the amount of electrons in the upper atmosphere — a property that has been measured by the MARSIS radar for over a decade across different seasons, areas of Mars, times of day, and more — and correlating it with the atmospheric parameters measured by other instruments on Mars Express.”
The Martian atmosphere behaves as a single system. Image credit: ESA / Mars Express / MARSIS / B. Sánchez-Cano et al.
The amount of charged particles in Mars’ upper atmosphere is known to change with season and local time, driven by changes in solar illumination and activity, and, crucially for this study, the varying composition and density of the atmosphere itself.
But Dr. Sánchez-Cano and colleagues found more changes than they were expecting.
“We discovered a surprising and significant increase in the amount of charged particles in the upper atmosphere during springtime in the Northern hemisphere, which is when the mass in the lower atmosphere is growing as ice sublimates from the northern polar cap,” she said.
Mars’ polar caps are made up of a mix of water ice and frozen carbon dioxide. Each winter, up to a third of the mass in the Martian atmosphere condenses to form an icy layer at each of the planet’s poles. Every spring, some of the mass within these caps sublimates to rejoin the atmosphere, and the caps visibly shrink as a result.
“This sublimation process was thought to mostly only affect the lower atmosphere — we didn’t expect to see its effects clearly propagating upwards to higher levels. It’s very interesting to find a connection like this,” said co-author Dr. Olivier Witasse, of the European Space Agency.
The finding suggests that the atmosphere of Mars behaves as a single system.
This could potentially help planetary researchers to understand how the planet’s atmosphere evolves over time — not only with respect to external disturbances such as space weather and the activity of the Sun, but also with respect to Mars’ own strong internal variability and surface processes.
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Beatriz Sánchez-Cano et al. Spatial, Seasonal, and Solar Cycle Variations of the Martian Total Electron Content (TEC): Is the TEC a Good Tracer for Atmospheric Cycles? Journal of Geophysical Research: Planets, published online May 31, 2018; doi: 10.1029/2018JE005626
