Deep within the cores of planets, extraordinary conditions give rise to peculiar and exotic forms of matter. One fascinating example is superionic ice, a substance that defies conventional understanding. Superionic ice is simultaneously solid and liquid, hot, dark, and heavy.
The Story of Superionic Ice
The quest to understand superionic ice began in 1988 when physicists hypothesized its existence. However, it wasn’t until 2017 that scientists managed to recreate this enigmatic ice in laboratory settings, confirming its existence and crystalline structure a year later. But the story didn’t end there. In recent years, researchers from esteemed American universities and the renowned Stanford Linear Accelerator Center laboratory in California made groundbreaking discoveries, unraveling the mysteries surrounding superionic ice.
The Enigmatic Nature of Superionic Ice
Water, a molecule composed of two hydrogen atoms and one oxygen atom, is usually considered a simple substance. However, under extreme pressures and temperatures, such as those found within planets like Uranus and Neptune, water undergoes a remarkable transformation into superionic ice. This unique form of ice exists at pressures approximately 2 million times that of Earth’s atmosphere and temperatures comparable to the surface of the Sun.
In 2019, scientists confirmed the previously hypothesized structure of superionic ice. Oxygen atoms arrange themselves in a solid cubic lattice, while ionized hydrogen atoms move freely, akin to electrons in metals. This peculiar structure grants superionic ice its conductive properties, allowing it to remain solid even at extraordinarily high temperatures.
Superionic ice is strangely different, and yet it may be among the most abundant forms of water in the Universe – presumed to fill not only the interiors of Uranus, Neptune, but also similar exoplanets: https://t.co/VtbsLY2yxD pic.twitter.com/rgBuZdvW3H
— Science Acumen (@ScienceAcumen) October 15, 2023
Discovering Ice XIX: The Experiment
In a recent study, physicist Arianna Gleason and her team from Stanford University conducted an experiment to simulate the extreme conditions within Neptune-like exoplanets. By subjecting water to intense pressure and temperature using powerful lasers, they recreated the environment where superionic ice forms. The experiment involved targeting thin layers of water trapped between diamonds and producing shockwaves that amplified the pressure to a staggering 200 GPa, equivalent to 2 million atmospheres. These conditions raised the temperature to approximately 8,500°F.
The Birth of Ice XIX
The results of Gleason’s experiment led to the discovery of a new phase of superionic ice, known as Ice XIX6. Ice XIX possesses a body-centered cubic structure, exhibiting even higher conductivity compared to the previously identified Ice XVIII6. This finding is significant as it sheds light on the enigmatic magnetic fields observed in Uranus and Neptune, which exhibit multiple poles and unpredictable orientations6.
Conductivity and Magnetic Fields
To understand the relevance of conductivity in the context of superionic ice, we must first explore the connection between charged particles in motion and magnetic fields. According to dynamo theory, moving charged particles generate magnetic fields7. This principle explains the origin of magnetic fields in Earth’s mantle and other celestial bodies7. If a Neptune-like ice giant contained a higher proportion of solid ice and less liquid, it would exhibit a different nature of magnetic field8.
Gleason and her team propose that the heightened conductivity of an Ice XIX-like superionic layer could be the key to the generation of the unconventional, multipolar magnetic fields observed in Uranus and Neptune8. The coexistence of two superionic layers with varying conductivity within a planet like Neptune would result in distinct interactions with the outer liquid layer’s magnetic field, leading to even more unconventional magnetic field behavior8.
Implications for Understanding the Cosmos
The discovery of superionic ice and its unique properties has far-reaching implications for our understanding of the cosmos. Over 30 years ago, NASA’s Voyager II space probe journeyed past Uranus and Neptune, recording their peculiar magnetic fields9. At the time, these magnetic fields remained a mystery, but the recent findings on superionic ice provide a potential explanation9. If verified, the heightened conductivity of Ice XIX-like superionic layers could account for the unconventional magnetic fields observed in these ice giants9.
As we delve further into the study of superionic ice, we are reminded that the universe is a constant source of mysteries, continually challenging and expanding our understanding. While the nuances of superionic ice are only just beginning to be unraveled, its implications for our comprehension of the cosmos are vast.