Scientists have developed a new model to better understand whether Mars once hosted water — and maybe even life.
The Martian surface is an inhospitable place: It is too cold for humans to live comfortably on it, and it lacks liquid water. But it was not always so. Some 4 billion years ago, the Red Planet was a very different place. It may even have hosted oceans. So what happened to make Mars lose its water, and, in turn, potentially its surface life?
At the time Mars is thought to have had liquid water on its surface, uit would have been very far from the Sun, and the Sun would have been dimmer than it is now (70 to 80 percent as bright as it is today). So something else must have been making Mars warm, and hospitable.
“The evidence for that comes in many forms," Timothy Lyons, professor of Biogeochemistry at University of California, Riverside tells Inverse.
"In particular, geomorphic features that clearly show that there was water that laid deposits like deltas and coastlines for these lakes and ocean margins and so forth. But it has been really, really hard to understand how that could be.”
"Mars must have had a lot of some gas, probably carbon dioxide in its atmosphere.”
In a new study, Lyons and his team suggest the answer may have to do with the carbon dioxide in Mars' atmosphere, and how much of a greenhouse effect it could have caused.
“Greenhouse gases keep planets warm by trapping heat near the planetary surface,” Lyons tells Inverse. “And so you almost universally come to the conclusion that Mars must have had a lot of some gas, probably carbon dioxide in its atmosphere.”
By closely analyzing the alkalinity, acidity, and nitrogen in Martian geology, scientists may finally paint a more precise picture of the Red Planet's environment — and reveal what really happened to Mars' water.
The model is detailed in a study published Wednesday in Science Advances.
The way the model works is this: The researchers can take a sample of surface material, and then trace its elemental composition. From there, they can work out the ratio of nitrogen isotopes. These "tell you a lot about what is going on," Christopher Tino, graduate student the University of California, Riverside and NASA Fellow, tells Inverse.
For example, by looking into the nitrogen isotopes of Martian geology, the researchers would be able to tell if Mars' water had very high pH, or not. If it is high, it means Mars had a lot of carbon dioxide in the environment.
“Using our understanding of nitrogen chemistry in the lake systems, particularly those that are similar to ones of Mars, we may have developed a way to track whether or not a lake system has a high pH or not,” Tino says.
“Whether or not it has a high pH is going to directly inform our understanding of the chemistry of that system and how it interacted with the atmosphere.”
The researchers suggest that Mars' atmosphere may have held the equivalent of half of our own atmosphere's carbon dioxide content. But it is — for obvious reasons — difficult, if not impossible, to work that out on Mars, so the researchers instead tested their ideas on an analogue: A crater found here on Earth.
The Nördlinger Ries crater
The Nördlinger Ries crater is perhaps the one place on our world that is as similar as it gets to Mars. The crater is in Germany, and formed 15 million years ago after a meteorite slammed into the Earth. There, the geology and chemistry is similar to that of Mars, the researchers say, with layers and layers of rocks and minerals.
This one spot, which has preserved its geology better than most places on Earth, was where the researchers were able to test their pH measuring tools.
“This crater system is analogous to what could have been happening on ancient Mars.”
Using the crater as a proxy environment is a good plan, Christian Schroeder, a researcher at Stirling University in the United Kingdom, tells Inverse. “And to have such a proxy, it is nice to be able to constrain the pH in that high range more precisely.”
But it isn't the perfect solution, he says. Nitrogen comes from the decay of organic matter, and we do not yet know whether there was organic matter and mass on Mars, he says. Schroeder was not involved in this study.
“This crater system is analogous to what could have been happening on ancient Mars,” Tino says.
The crater provides a test ground for their tool. Understanding the nitrogen isotope-ratio can inform on the pH levels — and that "can confirm what the atmosphere may have been like on Mars," he says.
Making it on Mars
There is a catch, however. The success of their tool rests on the Mars 2020 rover, which is supposed to launch in July, 2020. The rover is designed to land in a similar crater on Mars, called the Jezero crater. There it is to take samples from the Martian surface and store them for later transport back to Earth.
These samples could be analyzed for their nitrogen isotope ratios, and confirm the team's predictions. Unfortunately, they have some time to wait.
“The next years and are the time to prepare such proxies and improve our toolbox so that when the samples are finally returned from us, we have a lot of different tools to throw at them,” Schroeder says. The timeline for this might be within the next 10 to 20 years.
“The mission to bring the samples back have yet to be agreed on, and funded," Schroeder says. "There is a lot of uncertainty in the pipeline."
“It's not something that happens immediately, but hopefully everything will be concluded within the next decade," he says.
Abstract: High-pH alkaline lakes are among the most productive ecosystems on Earth and prime targets in the search for life on Mars; however, a robust proxy for such settings does not yet exist. Nitrogen isotope fractionation resulting from NH3 volatilization at high pH has the potential to fill this gap. To validate this idea, we analyzed samples from the Nördlinger Ries, a Miocene impact crater lake that displayed pH values up to 9.8 as inferred from mineralogy and aqueous modeling. Our data show a peak in 15N of +17‰ in the most alkaline facies, followed by a gradual decline to around +5‰, concurrent with the proposed decline in pH, highlighting the utility of nitrogen isotopes as a proxy for high-pH conditions. In combination with independent mineralogical indicators for high alkalinity,nitrogen isotopes can provide much-needed quantitative constraints on ancient atmospheric Pco2 (partial pressure of CO2) and thus climatic controls on early Earth and Mars.