“Moon Power”–Subsurface Tides on Jupiter’s Ocean Worlds Create Hotspots for Life

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“Moon Power”–Subsurface Tides on Jupiter’s Ocean Worlds Create Hotspots for Life

 

Ever since Voyager 1 spacecraft flew past Jupiter in March, 1979 (where a day lasts 10 hours), NASA scientists have been captivated by the mysteries

 

that have been unveiled. A new study argues that the four largest moons of the largest planet in the solar system –three of them harboring oceans

 

believed to 100 kilometers deep or more–may have a bigger influence on each other’s tides than the gas giant itself does. The findings suggest that

 

oceans on these moons could then generate more heat from friction and could be more suitable to hosting life than previously thought.

 

Rethinking the Galilean Moons

Researchers might have to reconsider their understanding of how these ocean moons evolved and where most of their heat is coming from according

 

to a new study in AGU’s journal Geophysical Research Letters suggests that these Galilean moons, might play a bigger role in the ebb and flow of each

 

other’s tides than the big planet they orbit does because of a phenomenon called tidal resonance. This newly discovered relationship between the

 

moons means researchers might have to reconsider their understanding of how these ocean moons evolved and where most of their heat is coming

 

from.

 

Ever since Voyager 1 spacecraft flew past Jupiter in March, 1979 (where a day lasts 10 hours), NASA scientists have been captivated by the mysteries

 

that have been unveiled. A new study argues that the four largest moons of the largest planet in the solar system –three of them harboring oceans

 

believed to 100 kilometers deep or more–may have a bigger influence on each other’s tides than the gas giant itself does. The findings suggest that

 

oceans on these moons could then generate more heat from friction and could be more suitable to hosting life than previously thought.

 

Rethinking the Galilean Moons

 

Researchers might have to reconsider their understanding of how these ocean moons evolved and where most of their heat is coming from according

 

to a new study in AGU’s journal Geophysical Research Letters suggests that these Galilean moons, might play a bigger role in the ebb and flow of each

 

other’s tides than the big planet they orbit does because of a phenomenon called tidal resonance. This newly discovered relationship between the

 

moons means researchers might have to reconsider their understanding of how these ocean moons evolved and where most of their heat is coming

 

from.

 

Although researchers have long considered the gravitational effects that Jupiter has on its ocean moons, they have until now neglected the potential

 

tides raised by the moons on each other.

 

 

(NASA’s Juno spacecraft revealed that rather than casting one “shadow” in Jupiter’s aurorae (above), the moon Io – Jupiter’s fifth – casts several, in a double wing-shaped pattern, while Jupiter’s largest moon, Ganymede, casts a double shadow)

 

Tidal Resonance –Larger Tides than Jupiter

The new paper, by researchers with the Lunar and Planetary Laboratory in Tucson, Ariz., argues for the first time that Galilean moons’ gravitational

 

pulls on each other, though smaller, could be producing larger tides than Jupiter does. That’s because they are more tidally resonant with each other.

 

Resonance is more about timing than size. If you’re pushing someone on a swing, for instance, timing your shove with the natural forward momentum

 

of the swing will ensure their next swing is higher. Jupiter does the gravitational equivalent of giving the swing a big push when it’s coming at you,

 

whereas the moons give each other the equivalent of little pushes on the upswing.

 

According to Hamish Hay, lead author of the new study and now a postdoctoral fellow at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., for

 

Jupiter to produce dramatic tides on its moons, the planet would have to be tidally resonant with the oceans of those moons.

 

Warm, Dynamic Oceans –Habitats for Alien Octopus?

 

In the new study, Hay and his colleagues calculated how tidal forces of Jupiter and other moons would affect the flow of oceans of different depths. For

 

Europa, for instance, they assumed an ice shell 10 kilometers (6 miles) thick.

 

They found that Jupiter’s pull could raise a tidal wave if Europa’s ocean were just 200 meters (660 feet) thick, which researchers think is unlikely. Io’s

 

weaker gravitational influence, on the other hand, could induce a sizable westward tidal wave in oceans up to 80 kilometers (50 miles) thick. The

 

researchers saw this trend for all the Galilean satellites, with moon-moon tides capable of producing many times more heat than Jupiter’s tidal forces

 

could possibly generate.

 

A warmer, more dynamic ocean is one that could potentially be more suitable to life.“That’s kind of interesting, because Jupiter is the biggest mass in

 

that system, so its tidal forces are much bigger than one moon on another,” Hay said.

 

Without tidal resonance, most of the heat within these oceans would be generated from radioactive decay of elements and Jupiter-raised tides in the

 

rocky portions of the moons. But if dramatic tides due to the other moons are also in play, the ocean could be generating its own heat from friction

 

with the icy shell it’s trapped under. A warmer, more dynamic ocean is one that could potentially be more suitable to life.

 

Tidal resonance could also help scientists pinpoint exactly how thick the Galilean moons’ oceans are. If the tides under the ice are strong enough, the

 

whole moon’s surface would pulse in and out, as though the moon were breathing.

 

“If you can measure the rate at which the moon’s surface is moving up and down, then that would be a way to tell you how thick the ocean might be,”

 

Hay said.

 

However, much of this research is still theoretical, he cautioned. The models used in the paper take only horizontal motion into account, just as they

 

would on Earth. If these oceans are actually over 100 kilometers (60 miles) deep, as most researchers think they are, there would also be a significant

 

amount of vertical motion to account for.

 

In addition, it isn’t possible to calculate the exact resonant frequency without knowing precisely how thick the moons’ oceans are. Although the moons

 

could have been tidally resonant with each other in the past, they might not be today.

 

In the future, Hay said, researchers could build on this work by modeling the way the oceans and their icy shells evolved together on these moons in

 

light of the potential for tidal resonance. This could completely change scientists’ views of the history of Galilean moons, Hay said.

 

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