Rapidly Freezing Saltwater Could Provide Spark of Life on Icy Worlds

The research team's results for WRE potential (Volts) for NaCl polycrystalline ice as a function of freeze rate (blue) compared with data from Wilson and Haymet (2010) (black). Credit: Johnson et al. 2014

The research team’s results for WRE potential (Volts) for NaCl polycrystalline ice as a function of freeze rate (blue) compared with data from Wilson and Haymet (2010) (black). Credit: Johnson et al. 2014

A research team has confirmed the existence of a process that causes the electrolysis of water, and which has the potential to drive the production of life in “Snowball Earth” scenarios and on icy satellites such as Europa and Enceladus.

The process, known as the Workman-Reynolds Effect (WRE), occurs when a dilute aqueous solution of salt rapidly freezes, causing ions in the solution to assume a negative or positive charge at the interface between ice and water.

Travis A. Johnson, a geosciences student at the University of Colorado at Boulder, said the WRE is the resulting electric potential that forms between the ice and its constituent diluted salt solution. This potential can range from a few to around 230 volts, and could lead to significant hydrogen (H2) and oxygen (O2) gas production, which are crucial elements in the formation of life as we know it.

Thermoelectric Cooling

The research team, led by Kevin Hand, deputy chief scientist of Solar System exploration at NASA’s Jet Propulsion Laboratory in Pasadena, California, is investigating the WRE using an apparatus made of thermoelectric cooling units designed to rapidly freeze various salt solutions in small quantities.

The team, which also includes Andrew Park, a Systems Engineer at Honeywell Aerospace, presented its initial findings at this years’ Lunar and Planetary Science Conference in Texas. The work was supported, in part, by the NASA Exobiology Program. The researchers initially focused their efforts on the study of various salts, including sodium chloride, potassium chloride, ammonium chloride, magnesium sulphate and sodium sulphate.

Jupiter's moon Europa, photographed by the Galileo spacecraft. Credit: NASA/JPL/University of Arizona

Jupiter’s moon Europa, photographed by the Galileo spacecraft. Credit: NASA/JPL/University of Arizona

As a result of work previously carried out by Hand using spectroscopic data gathered by the Galileo Near-Infrared Mapping Spectrometer (NIMS) instrument, it is now commonly believed that Europa’s ocean contains a significant amount of sodium and magnesium sulphates, due to radiation from the active volcanics in the neighboring moon Io, and Jupiter’s magnetic interactions with the two moons.

As Johnson explains, many scientists believe that what we observe chemically on the surface of Europa may strongly reflect what we might observe underneath its icy shell.

According to Johnson, the electrolysis of water not only produces hydrogen gas but a significant amount of oxygen as well and if this process were to occur over a larger period of time through a naturally consistent process such as the WRE, the amount of oxygen produced “would be substantial enough to support habitation.”

Future work with the WRE will also consider the effect that it has on dilute salt solutions with hydrocarbons present. Johnson believes that if conditions are right and hydrocarbons are present near the ice-water interface, the WRE “may provide enough electric potential to drive initial chemical reactions that are essential to the production of life.”

The team was initially skeptical about the existence of the WRE, as well as about previously published results that in some cases recorded potentials of up to around 230 volts. That’s equivalent to the voltage supplied by many residential mains systems around the world, and enough to power most modern electrical appliances. But Johnson says that initial results “have indicated that the WRE exists and is a natural effect that needs to be studied more closely with our modern instrumentation.”

The simple fact that the WRE is a “real observable phenomena” continues to motivate the team to research its possible applications on icy satellites, he says.

“Looking at Europa, we know that it contains a salty liquid ocean based on Galileo magnetometer results, and we know that throughout the formation of our solar system Europa had to have frozen over, likely rapidly, at some point,” says Johnson.

“These points alone provide us with enough certainty that the process of the WRE, or a very similar one, could have occurred on these icy satellites at some point and may even be occurring currently in rapidly freezing regions.”

Although the WRE provides enough energy to drive the process of electrolysis of water, Johnson stresses that the team has not yet determined if the WRE alone could “provide enough potential to drive the initial chemical processes that are essential to the production of life.”

High Variability

The Workman Reynolds Effect was first discovered in the late 1940’s when E. J. Workman and S. E. Reynolds reported that a potential arises between the ice-water interface of a dilute salt solution when it is rapidly frozen.

Current apparatus being used for freeze-up experiments. Credit: Johnson et al. 2014

Current apparatus being used for freeze-up experiments. Credit: Johnson et al. 2014

At first, the pair proposed that this effect was a possible mechanism for the generation of thunderstorm electricity, and with recorded potentials of up to 232 volts Johnson says that the results from Workman and Reynolds have been of continued interest to a small research community over the years.

However, as researchers began to explore the WRE in greater detail, the number of variables that affect the results, including factors such as salt type, concentration and freeze rate, became “problematic” and he says that the high variability of the resulting potential created “inconsistency with previously published results.”

For example, two more recent studies on the WRE published by P. W. Wilson and A. D. J. Haymet found greatly conflicting results, with one finding a potential electrical output of between 12 and 32 volts and the other declaring it was zero volts, even though the freeze rate and concentration of the solution were the same in each case.

“To give you a comparison, our initial results [using] the same freeze-rate and concentration used by Wilson and Haymet showed a peak WRE potential of around nine volts,” says Johnson.

Life Under ‘Extreme Conditions’

Because of the “great inconsistencies” reported in these previous studies, Johnson says that as part of the ongoing research the team aims to “deeply investigate the numerous factors of the WRE,” including the effects of “bottom-up versus top-down freezing.” Additionally, the team aims to study the significance of the effect when applied to icy worlds and in the conditions of Snowball Earth, the period in history when many scientists contend that the Earth’s surface became entirely or nearly entirely frozen.

Johnson also highlights the fact that the WRE is “extremely sensitive to outside factors,” and his advice to the astrobiological community is to continue research “on the basis that life finds a way to thrive in the most extreme conditions.”

For Johnson, the fact that the ice-water interface may be one such “extreme condition” means that it merits further investigation. In his view, the ability to remotely detect the WRE would aid scientists in collecting subsurface information regarding the dominant salt present in a subsurface ocean, as well its concentration, and the possible freezing rate that the ocean is undergoing.

“This information can help astrobiologists determine whether or not a particular planet or satellite is habitable,” Johnson says. “The biggest challenge ahead would be to fully and accurately catalogue the WRE potentials for various salt solutions at various concentrations as well as fully control all factors that affect the WRE.”