Earth’s oceans are a huge uniform electrolyte solution. They contain salt (sodium chloride) and other nutrients like magnesium, sulfate and calcium. We cannot survive without electrolytes, and life on Earth could be very different without the electrolyte content of the oceans. It may even be non-existent.
On Earth, electrolytes are released into the oceans from rock by various processes such as volcanism and hydrothermal activity.
Are these vital nutrients available on aquatic worlds?
What is an aquatic world?
Aquatic worlds are exoplanets containing enough water to form a hydrosphere. Many exoplanets we have discovered are super-Earths and/or mini-Neptunes, and scientists expect some of them to be water worlds. On these planets, electrolytes probably play a similar role in habitability as on Earth’s oceans.
But the problem is that super-Earths and mini-Neptunes are more massive than Earth, and their interiors are under more pressure than Earth. These planets can form deep planetary ice mantles between rocky cores and surface oceans. These ice barriers are no ordinary ice. Instead, they are high-pressure ices like Ice VII, and this dense ice could be a barrier that prevents essential mineral electrolytes from moving from the cores to the oceans, where they would be available for life.
These high-pressure ice shelves could limit the habitability of ocean worlds. But a new study suggests that electrolytes can pass through these icy cloaks onto aquatic worlds. If that’s true, there’s one more reason to be optimistic about life in these fascinating worlds.
What’s new – The study is “High-temperature salt ice stability suggests electrolyte permeability in the icy mantles of water-rich exoplanets.” It’s published in the magazine Nature Communicationand the main author is Jean-Alexis Hernandez, researcher at the European Synchrotron Radiation Facility.
“Electrolytes play an important role in the internal structure and dynamics of water-rich satellites and potentially water-rich exoplanets,” the article begins.
“However, on planets, the presence of a large, high-pressure ice mantle is thought to impede the exchange and transport of electrolytes between various liquid and solid deep layers.”
exotic ice cream
The ice in these coats is different from the ice on Earth. A range of ice types form under higher pressures on more massive planets. Regular atmospheric land ice is called Ice I. Researchers have created other types in laboratory experiments, from Ice II to Ice VII. In one experiment, researchers subjected a drop of water to a powerful shock wave and created Ice VII, although it only lasted for a moment.
In oceanic worlds that are super-Earths or mini-Neptunes, the deep layers of the ocean are likely frozen into high-pressure ice like Ice VII. Ice VII is structurally different from ice I. In ice VII, water molecules separate, oxygen ions crystallize, and hydrogen atoms move freely in the oxygen crystal lattice. According to the study’s simulations, nutrients can penetrate the ice.
Ice VII has an important feature when it comes to nutrient transport. While regular Earth ice expels salt as it forms, Ice VII can contain around 2.5% NaCl in its structure by weight. The NaCl in Ice VII lowers the melting point of ice and softens it. Thus, convection currents from the planet’s interior can propel NaCl upwards through the ice and into the ocean. This creates a temperature differential, and the ice cools and sinks. The result is a stream of recycling salt from the rocky interior of the planet, through the ice mantle into the ocean, and back again.
This can happen in our solar system. The researchers found evidence of hydrated mineral salts staining the surface of some of the icy moons. Moons like Ganymede, Callisto, Europa, and Enceladus all likely have subterranean oceans beneath their frozen shells, with HP ice mantles at varying depths that form barriers between their rocky cores and their oceans. Thus, the surface-staining minerals were transported through at least one layer of ice, possibly more. Some of the moons are not massive enough to form Ice VII, but Jupiter’s Callisto, Ganymede, and Saturn’s Titan are massive enough to form high-pressure ice mantles.
If nutrients like sodium chloride can be transported from a planet’s rocky interior through an ice sheet VII to the ocean, it could be a game-changer. Suddenly, there’s more evidence that these ocean worlds could support life.
Aquatic Worlds of Potential
As we find more exoplanets, we see more potential water worlds. The well-known TRAPPIST-1 system can host several of them – TRAPPIST-1e and TRAPPIST-1f are good candidates – although scientists are not sure. Kepler-62e and Kepler-62f are also possible water worlds.
Baptiste Journaux is a research fellow at the University of Washington, where he studies planetary science, including conditions in the deep planetary oceans. Newspapers commented on this new study in Nature Communication.
In his article, he said exoplanet discoveries show that ocean worlds are likely to be widespread. Our solar system has oceanic moons but no oceanic worlds. And while the Earth’s surface is two-thirds ocean, our planet is actually remarkably dry.
These new findings boosted the habitability potential of all ocean worlds, according to Journals.
“The study by Hernandez et al. offers the most compelling argument to date for solving the dilemma of the habitability of large planetary hydrospheres.
The study of oceanic exoplanets is all about simulations; there is no way to observe them in great detail. But the James Webb Space Telescope could start to change that. It may be able to detect spectroscopic fingerprints from interactions between an ocean planet’s atmosphere and its ocean. And more help is on the way.
The search for life
NASA and ESA are developing missions to some of the solar system’s icy/ocean moons. ESA’s Jupiter Icy Moons Explorer (JUICE) will launch in about a year and reach the Jovian system in 2031. In 2034, it will enter orbit around Ganymede, the largest moon in the solar system. It will eventually approach within 500 kilometers (310 miles) of the surface of Ganymede.
NASA’s Europa Clipper is scheduled to launch in 2024 and reach Jupiter by 2030. Although it will orbit Jupiter, it will study Europa, another oceanic moon with an icy shell.
Ganymede and Callisto are probably massive enough to form high-pressure water-ice blankets. Titan too, but it’s a long way off, and although there’s talk of a mission to Saturn’s largest moon, that’s far from certain.
Missions to these moons will begin to test some of the study’s findings. If electrolytes can be transported through high-pressure layers of ice on Ganymede, it will be a key discovery for habitability on water worlds. But life requires more than Na and Cl. We still don’t know if other important molecules can cross these ice barriers.
And after – Future missions will tell us a lot about the icy ocean moons of our solar system and the permeability of high-pressure ice mantles. Some of the findings will also be extrapolated to ocean worlds in other solar systems.
“These missions will not only allow us to better understand the inner workings of the hydrospheres of icy moons, but will be essential for understanding the largest oceans of our universe in water-rich exoplanets, their potential for habitability and their future characterization by modernity. .and next-generation telescopes,” Journals said in its article.
The authors of the new study end by talking about some of the other factors involved in the habitability of the ocean world.
They point out that electrolyte transport depends “…on the actual size, composition and surface temperature of the planet under consideration, which could result in different scenarios at the interface between the ocean and the mantle of ice, and between the ice mantle and the rocky core.”
Many factors must be right for an ocean planet to transport nutrients to the ocean surface. But at least they showed with their simulations that it is possible.
We will have to wait to find out if their simulations are correct and what the scale of the phenomenon is.
This article was originally published on Universe today by Evan Gough. Read the original article here.