New Mars Orbiter Manuever Challenges Theory: That May Not Be an Underground Lake on Mars

In 2018 researchers claimed evidence of a lake beneath the surface of Mars, detected by the Mars Advanced Radar for Subsurface and Ionosphere Sounding instrument (or Marsis for short).

But new Mars observations 'are not consistent with the presence of liquid water in this location and an alternative explanation, such as very smooth basal materials, is needed.' Phys.org explains

Aboard the Mars Reconnaissance Orbiter, the Shallow Radar (SHARAD) uses higher frequencies than MARSIS. Until recently, though, SHARAD's signals couldn't reach deep enough into Mars to bounce off the base layer of the ice where the potential water lies — meaning its results couldn't be compared with those from MARSIS. However, the Mars Reconnaissance Orbiter team recently tested a new maneuver that rolls the spacecraft on its flight axis by 120 degrees — whereas it previously could roll only up to 28 degrees. The new maneuver, termed a 'very large roll,' or VLR, can increase SHARAD's signal strength and penetration depth, allowing researchers to examine the base of the ice in the enigmatic high-reflectivity zone. Gareth Morgan and colleagues, for their article published in Geophysical Research Letters, examined 91 SHARAD observations that crossed the high-reflectivity zone.

Only when using the VLR maneuver was a SHARAD basal echo detected at the site. In contrast to the MARSIS detection, the SHARAD detection was very weak, meaning it is unlikely that liquid water is present in the high-reflectivity zone.

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