Paris , Nov 17: Results from the MARSIS (Mars Advanced Radar for Subsurface and Ionospheric Sounding) experiment have shed new details about the ionsophere of Mars.

MARSIS is one of the seven instruments of the ESA (European Space Agency) Mars Express Mission.

Although the main task of MARSIS is to probe beneath the planet's surface in search of unseen geological materials and structures, the radar is also a valuable tool for learning about the ionosphere. This is because the radio waves from MARSIS are reflected and modified as they pass through the ionised layer.

Earth's ionosphere has been studied intensively and is invaluable as a reflector of radio waves, but, until recently, little was known about the Martian ionosphere.

Previous measurements indicated that Mars' ionosphere generally lies about 110 to 130 km above the planet. In this region, high-energy solar radiation and particles in the solar wind split the atoms and molecules in the upper atmosphere, releasing free electrons.

Now, after 2 years of research work, an international team of scientists has been able to analyse more than 750 000 echoes from MARSIS in order to make the first direct measurement of the global distribution of electrons in the Martian ionosphere, or the total electron content (TEC).

The distribution of the TEC has been determined by using a novel transmission-mode's technique to sound the ionosphere, instead of the more common reflection mode.

In the transmission mode, the radar transmits a pulse that travels through the ionosphere twice, once on the way down to the surface and again on the way back. The received echoes are weakened, delayed and dispersed, depending on the electron density in the ionosphere directly below the spacecraft.

In the process of correcting the radar signal, the team has been able to estimate the TEC and its global distribution with an unprecedented spatial resolution of about 5 km.

"We have been able to analyse the MARSIS data to obtain the first large-scale coverage of the ionosphere above the planet's night side," said Ali Safaeinili of NASA's Jet Propulsion Laboratory, lead author on a scientific paper presenting the new results. "The ionosphere on the night side of Mars has never been mapped before," he added.

The mapping of the geographical variations in the night side TEC data reveals an intricate web of regions with high electron density. One of the most interesting discoveries has been the close correlation between the number of electrons in the night-side ionosphere and the direction of the local Martian magnetic field.

"We confirmed that the regions of high electron density are associated with strongly magnetised areas, especially south of the equator, near places where the magnetic field lines are perpendicular to the surface," said Wlodek Kofman, a co-author on the paper. "On Earth, this situation is only found at the two magnetic poles," he added.

In the coming years, as the low point of the spacecraft's orbit drifts further into the night side, MARSIS is expected to provide an even more precise map of the ionosphere and the regions where the solar wind connects to the Martian magnetic field.

MARSIS was developed jointly by the Italian Space Agency and NASA. (ANI)