3D radiogram of Mars’ north pole reveals a ‘hidden canyon’

Mars is the only known planet outside of Earth to have polar ice caps, but unlike Earth, Martian ice is mostly of the “dry” carbon dioxide variety. Naturally, there is great interest in better understanding the polar regions of Mars. A new analysis of Mars using data from NASA’s Mars Reconnaissance Orbiter (MRO) has revealed previously hidden structures beneath the north ice — as seen above by the Mars Global Surveyor. Researchers encountered undulating landscapes, impact craters and even a large canyon all buried beneath the ice.

The Mars Reconnaissance Orbiter has been observing the Red Planet from above since 2006. Its instruments include a special type of penetrating radar called Shallow Subsurface Radar (SHARAD). It emits radar waves between 15 and 25 MHz, which can travel up to 4 kilometers through material before returning to the orbiter. Its depth is about 15 meters. The instrument has been returning data on Mars’ ice caps and other regions for years, but the team at the Planetary Science Institute (PSI) has done something new with it.

Sharad was incorporated into MRO to complement the MARSIS radar on the Mars Express orbiter. MARSIS can bounce its radar waves deep into the planet, but SHARAD’s resolution is much higher. And with clever data processing, the PSI team maximizes effective resolution. The team processed years of 2D scans from SHARAD using advanced 3D imaging methods to remove noise and interference. The result is a sharp 3D image of the planet’s structure beneath layers of frozen carbon dioxide. This 3D “radargram” makes it possible to detect objects that are otherwise difficult or impossible to see.

The research is published in the journal Planetary Science. The image above is a composite, showing a single horizontal slice through the North Pole ice cap (known as the Planum Borium) below. Other sections are vertical slices. The dark area near the middle is a 300-km region that cannot be seen from MRO’s orbit. The data reveals surface details such as the right-hand shaft and the impact pit at the bottom of the horizontal slice.

The team believes this same technique can be used to create 3D representations of structures in other regions of the planet. Next, they plan to scour the planum borium data for more compressed impact craters and structures.

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