How Rocky Planets Can Fuel the Origins of Life

Fatima Husain | EAPS News
Thursday, March 8, 2018

In "The Planetary Battery for the Origins of Life: The Example of Mars" NASA JPL research scientist Vlada Stamenkovic describes how volatile gases may influence origins of life conditions on the red planet

A greater understanding of the red planet's evolution may elucidate parts of Earth's own evolutionary history. On a planetary scale, Mars and Earth are comparable. The two planets orbit the sun at roughly the same magnitude in miles per second, they have comparable axial tilts, similar lengths of day, and they both have metallic cores overlain by less dense materials. The major differences between the planets involve their distances from the sun and their overall size: Earth is approximately fifty million miles closer to the sun and is approximately ten times more massive than Mars. As a result, it is possible to treat Mars as a simpler, cooler planet than Earth. Though the knowledge of plate tectonics on Earth is relatively recent and still developing, little is understood about Mars' heat cycling evolution.

How heat is transported from a planet's interior to its surface is a function of many different features, including the size of the planet, the composition of the planet, and the processes that generate heat within a planet. Heat transport from planetary interiors to planetary surfaces ultimately controls geochemical cycling, which affects the habitability of a planet. With this approach in mind, research scientist at NASA Jet Propulsion Laboratory Vlada Stamenkovic opts to study planets and the life they may support "from the inside out."

The study of Mars' interior and its subsequent heat transport employs geophysical modeling to predict how heat flows from the inside to surface of the planet. Stamenkovic focuses on modeling the three-dimensional heat transport of the planet, and modeling how that heat transport evolves over time. Because thermodynamics drives particular geochemical reactions, how heat flows across a planet affects the composition and appearance of its surface. Mars, like Earth, has a varied topography as a result of differential heat flow across its surfaces, though the mechanisms and heat transport cannot be directly studied using the analytical tools active on the planet.

Previous studies of Mars planetary evolution employed the use of parameterized mantle convection models. However, the early models could not explain the formation of Martian crusts or the magnetic anomalies present on the planet. Stamenkovic began creating his four-dimensional parameterized thermal evolution model by beginning with a one-dimensional parameterized model of heat flow. Unlike previous modeling approaches, Stamenkovic applied his heat flow models through the planet in multiple radial segments, ultimately generating a three-dimensional model of heat flow from the interior of the planet that accounts for variations in the thicknesses of Martian crusts. How the heat flows over time comprises the fourth dimension of Stamenkovic's model.

The application of these models to understanding the evolution of volatile gases, such as hydrogen and methane, may shed light on Mars' potential habitability. Stamenkovic spoke heavily about serpentinization, the process by which iron and magnesium rich silicate minerals undergo hydration reactions to form secondary minerals and hydrogen gas. Through Fischer-Tropsch-type synthesis, the hydrogen gas may further react to form methane gas. Stamenkovic's model showed zones where serpentinization could occur on Mars, and further showed that the zones shift inwards towards the interior of the planet over time.

Further, Stamenkovic discussed the presence of oxygen on Mars in the context of brines and perchlorates. The abundant distribution of perchlorates on the Martian surface is well-understood through detection by the Curiosity rover. The presence of perchlorates is particularly important for habitability research because perchlorates lower the freezing temperatures of water, allowing for the creation of transient liquid waters on Mars. Further, oxygen is soluble in brines and the presence of water is a requirement for all life on Earth, so understanding how water is present on Mars is of interest for origins of life research. Though surficial transient liquid waters on Mars are not compatible with Earth-based terrestrial life, subsurface conditions on the planet may support less transient, hydrated perchlorates that are stable year-round. Stamenkovic used temperature and pressure data to model where oxygen could be dissolved in brines around Mars, and showed how the solubility of oxygen in brines varied over time as Mars' obliquity changed.

Given the potential oxygen solubility in brines on Mars, Stamenkovic suggested that Mars may have the conditions necessary to support anaerobic microbes, variable with time. For questions raised in origins of life research on Mars and beyond, Stamenkovic suggested, the answers may lie below the surface.

After his talk, Stamenkovic took part in a brief question and answer session with the audience over email. Selected questions and answers are included below.

Q and A

What do you find most engaging about global geophysics research?
I love the fact that we explore a region that we normally cannot see but that so significantly affects our life. I compare planet interiors with human organs; in order to know whether someone is really healthy, we gotta explore how the organs function, how they are connected, and how blood circulates. In a similar manner, exploring how heat and material flow in the planet interior contains clues to our planet’s origins and our future on the planet’s surface.

Also, I love that in order to understand planetary interiors, we must combine disciplines from theoretical physics, thermodynamics, QM, chemistry, and biology.

What do you think are the greatest challenges in your research?
Timescales and extreme conditions. The timescales on which planets evolve are in the order of millions of years, and the high temperatures and pressures that occur within planet interiors are very large. It is hence difficult to validate models with experiments on short timescales and low pressures and temperatures — and this introduces large uncertainties.

That’s why comparative planetology helps so much for understanding the depths below our own feet – each planet is a new data point.

Have you ever come across any major surprises during your research career?
All the time ;-). Planet interior evolution is a complex system, which—like many complex systems—can often behave very unexpected. When you try to solve a set of partial differential equations in more than 5 dimensions and have large uncertainties, then it’s almost impossible to predict what’s happening unless the math is done correctly. The behavior can be well explained once the math is done and the connection path is drawn, but it’s hard to do good “intuitive” predictions.

What do you think are the next steps in planetary subsurface and thermal evolution research? What are you most excited about in the future?Thermal evolution research has to become a probabilistic framework, away from one line as a function of time towards a phase space of possibilities all associated with quantitative probabilities. That’s today still not part of conventional geophysical thinking but is something that I have been trying to push forward (e.g., Stamenkovic & Seager 2016). Also, I think that we have to look at evolving, far from thermodynamic equilibrium, systems (e.g., Stamenkovic et al 2016). Both approaches call for better and faster computation, inclusion of uncertainties, and less unique answers— and are hence less often used.

I think that Mars is the best place (next to Venus, which is unlikely to become a common target for exploration anytime soon) to validate our models, and also the best place to search for signs of past or present life outside of Earth. Mars subsurface exploration (the best zone where we might find signs of extinct or extant life) is hence something that makes me very excited.

“Geophysics/Geodynamics – Deep Life” exploration on Earth is another aspect where I invest lots of my time. I think that the most interesting things happen across traditional academic boundaries.

Can you comment on the advantages or disadvantages of the privatizing space travel?
Disadvantage: less control, danger to go against ethical values, less security for human lives.
Advantage: speeds things up, allows for out-of-the-box thinking, spices up the spacegame.

If the answers to life on Mars lie below the surface, how might drilling technologies need to change to adapt to Martian exploration?
We need more sounding for subsurface water, clathrates, carbonates, and volatiles. This will need to lead to using finally Time-Domain Electromagnetic sounding technologies, Di-electric spectroscopy tools, amongst other tools. We have the tech, we just need the GO (= money).

Drilling has to be performed as deep as possible. On Mars ideally down to ~100s m-kms (that’s where we have the best chance for liquid water). We now have the tech to go on Mars to a few 10s m-100m – all what we need is to get money and a GO to do so.  To get to ~km, we need to invest money in tech development and testing. There are already great concepts at JPL but they need to be fostered.

A note about the author:
Fatima Husain is a graduate student MIT's Writing & Humanistic Studies Department. 

Story image photo credit: J. M. Winder, with thanks.

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