The fact that ice floats on liquid water is part of our daily experience. However, it is a phenomenon that, in a certain way, defies the laws by which other substances of nature behave. The H2O has peculiar characteristics with respect to other elements, and it is these properties that make this, the primordial element of life, responsible for ensuring the success of the living creatures of the Earth.
Aware of these peculiarities, and with the intention of studying in depth the characteristics of water at a temperature below 0 degrees, an international team of researchers has managed to keep the water liquid at -43 degrees Celsius. Although other experiments had previously observed this extraordinary capacity, the innovativeness of the study, published in the journal Physical Review Letters, lies in the technique used to measure its temperature.
The scientific team injected droplets of water about 6 microns in diameter, all with the same size, in a vacuum chamber , and to know if they were still liquid they illuminated it with a focused laser beam. The more the droplets traveled through the empty space, at a speed of 72 kilometers per hour, the more they cooled by surface evaporation.
“The key to obtain the droplet temperature with great precision is to analyze the frequency or wavelength, which ‘bounces’ in the drop of water itself,” researcher José María Fernández, of the Structure Institute, explained to Alienture. de la Materia and member of the Higher Council for Scientific Research (CSIC).
Thus, the team observed a correlation between these modes of resonance and the size of the drop, which, in turn, could relate to the temperature: the smaller the temperature, the lower the temperature.
“Analyzing the frequencies of the light that resonated in the droplets we were able to measure the temperature of this water, with an accuracy of 0.6 degrees,” explains Fernández.
The peculiarities of water
Water has a series of anomalous properties, such as its density. Its solid form is less dense than the liquid one, a feature that has allowed, for example, to preserve life at the bottom of frozen lakes during glaciations.
In addition, the fact that the melting of the polar ice caps does not change the sea level has been definitive to regulate the climate of the planet. “If you put an ice cube in a glass of water and observe how it melts, you will see that the water level remains constant in the glass,” exemplifies Fernandez.
The origin of the peculiar properties of water, which has almost no other substance, lies in how its molecules behave or, more specifically, how they are linked together.
The secret is in the hydrogen bridges, forming a three-dimensional network between the hydrogen molecules. This explanation would be responsible for the anomalies that we have described previously, although a detailed molecular explanation does not yet exist.
Given the evidence that water is a substance that behaves uniquely, and that it is essential for life, it is inevitable to ask if liquid water could exist at temperatures never seen on Earth in other corners of the universe.
“We must bear in mind that droplets of liquid water at 43 degrees below zero of the experiment had a life of just a few milliseconds,” acknowledges the researcher. “It is not easy that in nature there is water under these conditions, although liquid droplets have been detected at -35ºC in high clouds of the Earth’s atmosphere,” he says.
However, Fernandez does recognize that under extraordinary states of pressure, water could behave in ways we do not expect. This leads one to think that, perhaps, the conditions can exist for liquid water to exist in extremely low temperatures, for example, under the ice of moons such as Europa or Enceladus, thus being able to harbor extraterrestrial life in its hypothetical oceans.