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article imageEssential Science: Saturn’s moon contains an underground ocean

By Tim Sandle     Oct 17, 2016 in Science
Reviewing data from the Cassini spacecraft, astrophysicists think there’s a strong chance that the Saturnian satellite Dione contains a vast underground ocean.
Dione is a moon of Saturn. It was discovered by Italian astronomer Giovanni Domenico Cassini in 1684. Dione is the fifteenth largest moon in the solar system, and it is more massive than all known moons smaller than itself combined.
The evidence is that a subsurface sea could be hiding beneath the icy crust of Dione. This is the finding of a report made to the journal Geophysical Research Letters (“Enceladus's and Dione's floating ice shells supported by minimum stress isostasy”). The research was undertaken by Mikael Beuthe, a planetary scientist at the Royal Observatory of Belgium in Brussels, and colleagues.
The storm can be seen on upper part of the image of Saturn
The storm can be seen on upper part of the image of Saturn
Image Credit: NASA/JPL-Caltech/SSI
This ocean would be 100 kilometers below the surface and be a mind boggling 65 kilometers deep. Evidence for the underground ocean comes from measurements of Dione’s gravity made by the Cassini spacecraft.
In an interview with Space Flight Now, lead researcher Mikael Beuthe said why an ocean is likely: “as an additional principle, we assumed that the icy crust can stand only the minimum amount of tension or compression necessary to maintain surface landforms. More stress would break the crust down to pieces.”
Artist s impression Cassini during the Saturn Orbit Insertion
Artist's impression Cassini during the Saturn Orbit Insertion
The Cassini spacecraft was in orbit around Saturn since 2004. However, such is the vastness and complexity of the data gathered, researchers are still interpreting the findings.
Cassini–Huygens is an unmanned spacecraft sent to the planet Saturn, and its mission continues as of 2016. The spacecraft design consisted of a Saturn orbiter (Cassini) and a lander (Huygens), for the moon Titan. The two spacecraft are named after astronomers Giovanni Cassini and Christiaan Huygens. One of the orbiter’s missions was to determine the composition of the Saturnian satellite surfaces and the geological history of each object.
Other planetary bodies in the solar system may also contain underground oceans, including Enceladus (another moon of Saturn), several moons of Jupiter, and possibly the dwarf planet Pluto.
An image obtained by Cassini showing the geyser basin at Enceladus south pole with water vapor jets ...
An image obtained by Cassini showing the geyser basin at Enceladus south pole with water vapor jets clearly visible.
NASA/JPL-Caltech/Space Science Institute
Both Dione and Enceladus are freezing, with temperatures of about minus 200° Celsius at the surface. However, heat generated by friction as Saturn’s gravitational pull could keep the buried sea liquid warmer. Evidence for underground water being hotter is shown by geysers erupting on Enceladus.
In addition, the Cassini satellite spotted small silica particles inside one of Saturn’s rings. These could originate from the bottom of Enceladus’ ocean by those gushing geysers (see the journal Icarus and the article “Enceladus’s measured physical libration requires a global subsurface ocean”).
Furthermore, as the website Science reports, Jupiter’s moon Europa could be venting water into space. If so, this would add support to the idea that an ocean hides beneath the moon’s thick shell of ice. With Pluto, the possible presence of an ocean is based on the dwarf planet’s alignment. Here Pluto is positioned in line with gravitational forces from Charon, Pluto’s largest moon, which might be the result of a vast underground ocean.
The significance of some of these oceans are that they would be a great place to search for extraterrestrial life (such as microorganisms). This will vary between satellites and the suspected temperatures of the oceans. Life is less likely beneath Pluto than it is with Dione and Enceladus.
Being able to device a spacecraft that could retrieve and analyse a sample, however, is a long way off. However, NASA is planning a spacecraft to fly by the moon Europa dozens of times and to set a lander down on Europa’s frozen surface during the 2020s. In addition, Enceladus and Saturn’s largest moon Titan have been added to the list of potential destinations.
This article is part of Digital Journal's regular Essential Science columns. Each week we explore a topical and important scientific issue. Last week we looked at how nanotechnology is improving the material used to make bulletproof clothing for combat personnel. The previous week we considered new research which shows the hidden life in the depths of the oceans.
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