https://phys.org/news/2025-11-liquid-mars.html
Ancient Mars boasted abundant water, but the cold and dry conditions of today make liquid water on the Red Planet seem far less probable. However, the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) detected strong radar reflections from a 20-kilometer-wide area over the base of Mars's southern polar ice cap, hinting at the possibility of liquid water below the icy surface. Such a finding would have major implications for the planet's possible habitability.
But sustaining liquid water underneath the ice might not be feasible without very salty brines or localized volcanic heat. Scientists have deliberated about other possible "dry" explanations for the bright reflections detected by MARSIS, such as layers of carbon dioxide and water ices or salty ice and clay causing elevated radar reflectivity.
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°—whereas it previously could roll only up to 28°. 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.
The researchers suggest that the faint detection returned by SHARAD under this portion of the ice cap is likely due to a localized region of smooth ground beneath the ice. They add that further research is needed to reconcile the differences between the MARSIS and SHARAD findings.
More information: Gareth A. Morgan et al, High Frequency Radar Perspective of Putative Subglacial Liquid Water on Mars, Geophysical Research Letters (2025). DOI: 10.1029/2025gl118537
(Score: 1) by anubi on Monday November 24, @06:41AM
For what it's worth, my interest was piqued and I asked Chat GPT. Here is my prompt and reply:
From Chat GPT:
Drop your image here
Chats
New
I understand Earth gravity is insufficient to retain helium. Once it released, it goes up until the solar wind blows it away .
Is Mars gravity sufficient to retain water vapor?
.
GPT-4o mini
Mars Gravity and Water Vapor Retention
Mars has a surface gravity that is about 37.6% that of Earth. While this lower gravity does present challenges for retaining atmospheric components, it is still possible for Mars to hold some water vapor.
Water Vapor on Mars
Mars does have a very thin atmosphere, primarily composed of carbon dioxide. However, this atmosphere does contain some water vapor, albeit in small amounts. The retention of water vapor on Mars is influenced by several factors:
Temperature: Mars is much colder than Earth, with surface temperatures often dropping below freezing, which can lead to condensation and frost formation.
Atmospheric Pressure: The thin Martian atmosphere exerts less pressure than Earth's, making it more difficult to hold vapor in gaseous form.
Solar Wind and Radiation: Mars lacks a significant magnetic field, making its atmosphere susceptible to erosion by solar wind and cosmic radiation. This can further limit its ability to retain water vapor.
Conclusion
While Mars retains some water vapor due to its gravity and atmospheric conditions, the challenges posed by its thin atmosphere and lack of magnetic protection mean that it cannot hold large quantities of water vapor over long periods. Any water vapor released can eventually escape
"Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]