science

On Saturn’s moon Enceladus, the ocean appears to be waving

Enceladus Plume

An artist showing a clear view of the interior of Saturn’s moon Enceladus. An aerosol of ice particles, water vapor and organic particles from fractions of the moon’s south polar region. Credit: NASA / JPL-Caltech

Buried under 20 kilometers of ice, the subsurface ocean of Enceladus – one of them SaturnIts moons appear to be flapping currents similar to those on Earth.

The theory, derived from Enceladus’ cryosphere shape, challenges the widespread belief that the moon’s global ocean is homogeneous, except for some vertical mixing caused by the warmth of the moon’s core.

Enceladus, a small frozen sphere about 500 km in diameter (about 1/7 the diameter of Earth’s moon), is Saturn’s sixth largest moon. Despite its small size, Enceladus attracted the attention of scientists in 2014 when it flew over the surface of the moon Cassini The spacecraft detected evidence of its large subterranean surroundings and took samples of water from geyser-like explosions that occur through cracks in ice in Antarctica. It is one of the few locations in the solar system with liquid water (another location JupiterMoon Europa), making it a target of interest for astrobiologists looking for signs of life.

Enceladus Global View with Plum

This illustration shows Saturn’s icy moon Enceladus with a column of ice, water vapor, and organic particles scattering from fractures in the moon’s south polar region. Credit: NASA / JPL-Caltech

The ocean on Enceladus is almost completely different from that on Earth. The circumference of the Earth is relatively shallow (average 3.6 kilometers deep), it covers three quarters of the planet’s surface, it is warmer in the upper part of the sun’s rays and cooler in the depths near the sea floor, and it has currents that are affected by the winds; Meanwhile, Enceladus appears to extend over the globe and have an ocean just below its surface that is at least 30 kilometers deep and is cooled at the top near the ice crust and warmed at the bottom by heat from the Moon’s core.

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Despite their differences, California Institute of Technology graduate student Anna Lobo (MS ’17) notes that the oceans on Enceladus have currents similar to those on Earth. Work builds on measurements by Cassini In addition to research by Andrew Thompson, a professor of environmental science and engineering, who has been studying the way ice and water interact to drive ocean mixing around Antarctica.

The oceans of Enceladus and Earth share one important characteristic: they are salty. As the results published in Natural Earth Sciences On March 25, differences in salinity could act as drivers of oceanic circulation on Enceladus, just as they do in Earth’s Southern Ocean, which encircles Antarctica.

Lobo and Thompson teamed up with Steven Vance and Saikiran Tharimena Jet Propulsion Laboratory, And operated by Caltech NASA.

Gravity measurements and heat calculations from Cassini It has already revealed that the ice crust is thinner at the poles than at the equator. Thompson says areas of thin ice at the poles are likely to be associated with melting and areas of thicker ice at the equator with freezing. This affects ocean currents because when salt water freezes, it releases salts and makes the surrounding water heavier, causing it to sink. The opposite occurs in the melting regions.

“Knowing the distribution of ice allows us to establish constraints on circulation patterns,” explains Lobo. The ideal computer model, based on Thomson’s studies of Antarctica, would indicate that regions of freezing and thawing, defined by the structure of the ice, would be related to ocean currents. This creates a pole-to-equator rotation that affects heat and nutrient distribution.

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“Understanding the subterranean regions of the ocean that may be most suitable for life as we know it could someday help in the search for signs of life,” Thompson says.

The reference: “The Inversion of the Ocean from the Pole to the Equator on Enceladus” by Anna H. Lobo, Andrew F Thompson, Stephen de Vance and Saikiran Tharimina, 25 March 2021, Natural Earth Sciences.
DOI: 10.1038 / s41561-021-00706-3

The title of the paper: “Circumference from the Pole to the Equator, Upset the Circulation on Enceladus”. This work was supported by the Jet Propulsion Laboratory’s Strategic Research and Technology Development Program. The Ice World knot at NASA’s Institute for Astrobiology; The David and Lucille Packard Foundation.

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