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Mars might not be in the news as often as Earth, but our planetary neighbour is having a big October. 

NASA announced last week that analysis of light spectra from streaks observed by the Mars Reconnaissance Orbiter suggest the briny residue of water. This is not the discovery of life, but it shortens the speculative leap. 

Meanwhile, the 3D movie The Martian had a $55-million opening weekend. And Canadian-American entrepreneur Elon Musk has generated headlines with a fanciful proposal to detonate fusion bombs in the Martian atmosphere.

The real science on the Red Planet, however, is more likely to last. �Թϱ��� spoke with Professor Rebecca Ghent of the department of Earth sciences, who is part of a team that will send a ground-penetrating radar instrument to Mars on the next rover, which is slated for launch in 2020.

Were you surprised by the spectrometry results? 

The features that the authors examined are called recurring slope lineae, or RSL, and people have been looking closely at them for some time. The briny water hypothesis has been the leading idea for their origin at least since 2012, and so the announcement of the detection of the brine signature was not wholly unexpected. The transient nature of the RSL has always suggested that a volatile substance was involved, either directly (i.e., the RSL consist of flows of that volatile [substance], such as water, mixed with regolith or other materials) or as a mobilizing agent (e.g., water or some other volatile flowing in the subsurface acted to dislodge fine granular materials, freeing them to flow downslope). 

Do you think this team has interpreted the data correctly?

I haven't looked at the spectrometry data myself, nor am I a spectroscopist, and so can’t personally say whether or not the team’s interpretation is correct. However, it is certainly the case that many other teams are and will be looking at those data and continuing to collect new data in order to verify or dispute these findings. I'm sure that we’ll hear more about this at the American Geophysical Union meeting in December and the Lunar and Planetary Science conference in March.

The paper concludes that the results “strongly support the hypothesis that seasonal warm slopes are forming liquid water on contemporary Mars.” Is this conclusion justified?

The idea that the liquid water, or brine, is contemporary comes from the fact that the RSL appear and disappear in images. This is a clear indication that the mechanism responsible for their formation is operating right now, and is something transient, as evaporation of water would be.

Are there rival explanations for the RSL?

Yes, there are, but the transient nature of the RSL ultimately indicates the involvement of some volatile. This could be water, as proposed in the recent article, or CO2, which is the main component of the thin Martian atmosphere. Recent results support the former hypothesis, but other researchers will continue to examine the data and their interpretation critically.

We read reports that very briny water is toxic to the touch. How can this be consistent with its role in the support of life?

Brines have often been proposed as possible habitats for Martian microbial life, if it exists. This is because the salt in the water depresses the freezing point and would allow water to be liquid at shallow depths below the surface on Mars, where fresh water would freeze and possibly sublimate. On Earth, specialized communities of microbes live in briny conditions, and the idea here is that similarly specialized species could be present on Mars. Certainly, at this point, the existence of some form of microbial life on Mars cannot be ruled out – but we have yet to make a positive detection of any kind of biological activity.

As a planetary scientist you focus on geology. Is there too much stress on the life question? Does the exploration of Mars result in other sorts of knowledge?

The exploration of Mars has led, independently of the search for Martian life, to a complete revolution in our ideas about how the planet works.  I’ll just cite a few examples here.  Using sounding radar, we have discovered that despite the enormous weight of ice on the Martian polar caps, the lithosphere [the rigid shell of a planet including the crust and upper mantle] beneath them does not flex. This either means that the lithosphere is very thick and rigid, or that the polar caps are very young, so the lithosphere hasn’t had a chance to respond, as Earth’s lithosphere did beneath the continental glaciers during the last ice age. (It’s still rebounding in Canada following removal of the ice.) Radar results have also showed that the polar caps are largely composed of water ice, with a thin layer of CO2 [dry ice] frost.

Are Martian discoveries relevant to Earth science?

Radar observations of non-polar cap regions have revealed buried channels, invisible from the surface, indicating a rich geological history. There are literally thousands of new results like these, from pictures, spectral results, radar, thermal infrared data, gamma ray spectrometer results, etc. Together, they are continuing to lead to a deeper understanding of the way that Mars works as a planet, inside and out.  The similarities and differences between Mars and Earth, and the other terrestrial planets, continue to help us put Earth’s processes in perspective.

Do you support further Mars research or do we have all the data we need?

I definitely support further Mars research. The ground-penetrating radar instrument on the next rover, slated for launch in 2020, will provide the first ground-based subsurface imaging for Mars. We’ll work closely with the other rover instrument teams to relate those subsurface measurements to the pictures, spectra, and other measurements made at the surface. In terrestrial geology, we depend on that critical vertical dimension to reveal the processes that have led to the current state. This experiment will give us the opportunity to do the same thing on Mars in a completely new way.

Which other Martian missions should we look forward to?

I’m very excited about the InSight, the robotic lander whose launch is scheduled for March 2016. That mission will send a suite of geophysical instruments that will provide much-needed new information about fundamental whole-planet processes, by measuring seismic activity, crustal heat flow and characteristics of Mars’s rotation. Understanding the planets of our solar system is a continuing process, one that’s extremely exciting, and goes far beyond the search for microbial life. We’ve barely scratched the surface, and each new discovery gives us a new understanding of the fundamental processes that drive our solar system, including Earth.