One of the most difficult things to reconcile in science is when new data either complicates or refutes previous knowledge. It is even more difficult when these results have been widely disseminated and made known in the community. But that’s how science works – the theories have to match the data. When a team at JPL analyzed Mars Express data on Mars’ South Pole, they found that the results published in 2018 on underground lakes on Mars may have been more difficult than they originally thought.
This original discovery was announced after scientists found particularly bright spots in radar signals below the surface, which were interpreted as being from liquid water. Located in the region known as the “South Polar Stratified Deposits”, layers of water, dry ice, and dust have mixed for millions of years as the axial tilt of Mars changed. In the lower layers, the temperatures were high enough that sufficient salty water could potentially be liquid.
UT video about the possibility of life (and water) on Mars.
Looking through the data for the entire South Pole of Mars, the JPL scientists noticed the same highly reflective surface in dozens of other places below the surface. Some appeared to be within 1 mile of the surface. Unfortunately, this also means the temperature would be a cool -63 C (-81 F). Even with an enormous amount of perchlorates (a special type of salt found on Mars), water would still freeze at these temperatures.
First, investigators, Jeffrey Plaut and Aditya Khuller from JPL (Khuller is now with ASU) tried to think about other potential sources of heat that could raise the temperature in the areas where they saw the highly reflective features. An obvious candidate would be volcanism, which may be responsible for submarine oceans on other worlds in the solar system. However, there is no other evidence of active volcanism at the South Pole, so the researchers ruled it out as a heat source.
Visualization from the original 2018 study showing the reflected radar signals interpreted as lakes.
Credit Context Card: NASA / Viking; THEMIS Background: NASA / JPL-Caltech / Arizona State University; MARSIS data: ESA / NASA / JPL / ASI / Univ. Rome; R. Orosei et al. 2018
Also, since there is a lack of heat to create liquid water, the researchers have no idea what these highly reflective surfaces could possibly be causing. Could it be lakes caused by heat from an unknown source? Is there any other material that is as reflective to radar as liquid water beneath the surface of Mars? The details of a future manned mission to the Red Planet could literally depend on the answer to these questions. But at the moment there is no satisfactory answer.
Put simply, either there are dozens of underground lakes on Mars that are heated by an as-yet-unknown source, or there could be an unknown material that reflects radar waves as effectively as liquid water, which led scientists to believe that there was liquid water there is available. Or it could be a combination of the two, with liquid water in some warmer pockets while the unknown material is in colder regions. According to other research just reported by UT, there are several possibilities in between.
Points on this map of Mars’ South Pole show where radar reflections were recorded by the MARSIS instrument used by JPL scientists.
Credit – ESA / NASA / JPL-Caltech
Given the importance of water to the success of any human presence on Mars, researchers will want to know where on this spectrum the truth lies. And the only way to find out is to collect even more data. Let’s hope the data we have gathered will answer more questions than it raises next time.
Learn more –
JPL study examines Mars’ underground water signals in more detail
UT – Unfortunately, there are other workable explanations for the underground lakes on Mars
Phys.org – “Lakes” under the South Pole of Mars: A cloudy picture?
Geophysical Research Letters – Characteristics of the Basal Interface of the Mars-South Polar Layer Deposits
Mission statement –
Ice cap at the south pole of Mars, which contains frozen water as well as dry ice.
Credit – ESA / DLR / FU Berlin / Bill Dunford