The interior of the Martian north polar cap can now be seen in much greater detail thanks to a newly enhanced 3D radar image. A team led by Planetary Science Institute Senior Scientist Nathaniel Putzig used data from NASA’s Mars Reconnaissance Orbiter’s Shallow Radar (SHARAD) instrument to create and study the 3D radargram image.
“In creating 3D radargrams, we assemble all the data from many 2D profiles across the region of interest and apply advanced 3D imaging methods to unravel all of the interferences present in the 2D profiles, placing the reflected signals at their points of origin to produce a geometrically corrected 3D image of the subsurface,”
said lead author Putzig.
Perspective view of the interior of Planum Boreum.
This cut-away view shows one horizontal slice (at bottom) and two opposing vertical slices through the north polar cap of Mars as seen by the MRO radar sounder.
The black circle in the middle is centered on the north pole with a diameter of 300 kilometers and represents an area that the radar does not see from MRO’s orbit.
Scales vary in this view, which shows the upper 2 kilometers of the 1200-kilometer-wide Planum Boreum at a vertical exaggeration of 150:1.
Credit: PSI/ASI/JPL/NASA.
Many Mars features that were previously difficult or impossible to map due to incomplete imaging of inherently 3D features with a collection of 2D profiles are brought into sharp relief by the new 3D radargram.
“So far, we have only scratched the surface of understanding what the new data volume is telling us about the history of Martian polar processes and climate, and there is a lot more detailed mapping work to be done,”
Putzig said.
Shallow Radar, Deep Scan
With a desired depth resolution of roughly 15 meters, the Shallow Radar instrument scans the subsurface up to 4 kilometers deep by emitting radar waves in the 15 to 25 megahertz frequency range. The SHARAD antenna picks up the returned radar waves, which are sensitive to changes in the electrical properties of any rock, sand, or water ice that may be present on the surface or below.
Comparison of features in 2D and 3D radargrams.
(a) US RDR 2D radargram for observation 5777-02.
(b) Incoherently summed 2D radargram along the track of observation 5777-02.
(c) Profile excerpted from the PB3Dv1 radargram along the track of observation 5777-02.
(d) Profile excerpted from the PB3Dv2 radargram along the track of observation 5777-02. For each panel, the power is displayed in grayscale such that the highest powers are white and lowest powers are black.
The vertical axes are in two-way travel time. Red arrows point to examples of clutter in the 2D radargrams that are cleared up in the 3D radargrams. Y
ellow boxes draw attention to zones of differences in resolution and geometric distortion between the panels.
The inset in panel (d) shows the location of the 2D radargram track along A–A’ across Planum Boreum in MOLA shaded relief.
Credit: Nathaniel E. Putzig et al CC-BY
Changes in the reflection characteristics of the subsurface are also visible, caused by layers deposited by geological processes in Mars’ ancient history.
By offering a sharper view of subsurface features, the 3D imaging results aid in our knowledge of Mars and can be used to support geologic interpretations of the origins of the polar deposits and their implications for the history of the Martian climate.
“The details of the subsurface layering geometry can be used to infer the processes involved in the deposition and erosion of the layers over time,”
Putzig said.
The permanent ice cap of Planum Boreum, the northern polar plain of Mars, is primarily made of water ice (with a 1 m thick carbon dioxide ice veneer during the winter). that encompasses an area roughly 1.5 times the size of Texas.
Reference: Nathaniel E. Putzig et al, New Views of the Internal Structure of Planum Boreum from Enhanced 3D Imaging of Mars Reconnaissance Orbiter Shallow Radar Data. The Planetary Science Journal 3 259DOI 10.3847/PSJ/ac9d3b
