Is there an underwater lake on Mars? Different researchers are coming to different conclusions. Some say that the Mars Express has shown liquid water in an underground lake. Some researchers say clays or minerals explain the data better.
Who is right? Maybe none of them.
A new study says volcanic rock can explain the Mars Express data.
A team of researchers published a paper about the data from the MARSIS instrument on the Mars Express. The data showed that the surface was very reflective. The Mars lake hypothesis gathered steam after the researchers concluded that water was responsible for the signal.
Other researchers gave different explanations for the signal, showing how clays and minerals might be involved. Scientists interpreted the data from MARSIS to show more reflective areas. The authors of the paper that started it all published a research letter re-affirming their original interpretation of the data and refuting research that reached different conclusions.
A group of scientists published a paper saying the other researchers are wrong. The MARSIS signal was caused by volcanic rock.
The lead author of the paper is Cyril Grima, a planetary scientist at the University.
There is a hypothesis that there is water under the SPLD. The temperature can be too low if the water is briny. There is more detail than that involved. That is the essence of it. Different materials have different permittivity at different temperatures. Scientists don't know what the temperature is.
Some of the concerns are set aside by this paper.
Cyril Grima is the lead author of the book, "For water to be sustained this close to the surface, you need both a very salty environment and a strong, locally generated heat source, but that doesn't match what we know of this region."
This new research suggests that a type of volcanic rock that is relatively common on Mars is responsible for the MARSIS data. If some of the volcanic rock was buried under the ice, it would look like water.
Grima and his co-authors used computer models to create a global sheet of ice. The researchers were able to compare features all across Mars with those under the real ice at the south pole. The team duplicated 10% of the SPLD in their simulation ice.
The result?
The team found bright reflections under different latitudes. The locations of volcanic rock were matched by many of them. The MARSIS signal could be produced by between 3% and 2% of the surface of Mars. The bright terrains the team detected are gathered within volcanic constructs.
Some volcanic terrains on Mars produce the same signal. A broad region of strong reflections is identified East of the Uranius Tholus, which is believed to be a shield volcano.
There is a fascinating scientific debate going on over the potential water under the SPLD. It draws attention to the fact that the bright terrains across the planet would produce echoes with a radiometric character in the range of the bright ones observed at the SPLD.
The paper says that the radiometric similarity is indicative of the likelihood for a non-wet generic material currently available at Mars to be responsible for the bright SPLD reflection. The iron-rich volcanic rock is common on Earth.
What do scientists on the other side of the issue think?
Dr. David Stillman works at the Southwest Research Institute. He is a co-author of papers that support the liquid water hypothesis.
The Grima paper is very good, according to Dr. Stillman. If we can point them out, he identifies some potential discrepancies.
The paper assumes that surface MARSIS amplitudes can be compared even though they were processed onboard Mars Express. The Italian group didn't process the data so that it could be compared when Mars was different. Scientists have to work with assumptions about the temperature under the SPLD. The MARSIS signal is affected by the temperature.
Grima and his co-authors used a figure to present some of their findings. It shows how volcanic rock can account for the signal on the surface of Mars, as well as four areas that show high reflectivity under the ice sheet.
The fact that the four regions are spread across the same location is a strength of the results.
There is another possibility for those signals, according to Dr. Stillman.
If you look at the paper, you will see that the northern plains of Mars have high surface reflection due to artifacts from onboard processing.
The majority of the artifacts are in what we believe to be sediments and could not have high dielectric values or reflectivity, according to Stillman.
This won't be the end of the debate, but it does show how complex the problem is.
The issue is important to many in the community. Even though Martian polar scientists form a fairly small, tightly-knitted community, it gets a lot of attention and commentary from other researchers on the internet.
Smith is not involved in any of the studies. Smith explained in a press release that the highly reflective signal could be explained by a type of clay dissolved in water. This phenomenon can be seen on Earth and could be on Mars.
Smith points out that if Grima is correct about the reflective signal, it's not bad for the larger issue of Martian water.
I think the beauty of Grima's finding is that it gives us precise places to look for evidence of ancient lakes, even though it knocks down the idea of liquid water under the planet's south pole today.
We are in a position between competing hypotheses. We are not stuck. This is how science works.
Smith said that science isn't perfect on the first try.
Dr. Stillman points out that everyone is forced to make assumptions when it comes to Mars.
He told Universe Today that he doesn't know which assumptions are correct because we are studying a planet so far away.
There are no papers that prove there is water or that there isn't. We are inching our way toward knowing for sure.
We need another mission to Mars because we need better data.
That is never a bad thing.
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