Jupiter's moons could be warming each other

Date:
September 10, 2020
Source:
University of Arizona
Summary:
The gravitational push and pull by Jupiter's moons could account
for more warming than the gas giant Jupiter alone.



FULL STORY ========================================================================== Jupiter's moons are hot.


========================================================================== Well, hotter than they should be, for being so far from the sun. In a
process called tidal heating, gravitational tugs from Jupiter's moons and
the planet itself stretch and squish the moons enough to warm them. As
a result, some of the icy moons contain interiors warm enough to host
oceans of liquid water, and in the case of the rocky moon Io, tidal
heating melts rock into magma.

Researchers previously believed that the gas giant Jupiter was responsible
for most of the tidal heating associated with the liquid interiors of the moons, but a new study published in Geophysical Research Letters found
that moon-moon interactions may be more responsible for the heating than Jupiter alone.

"It's surprising because the moons are so much smaller than Jupiter. You wouldn't expect them to be able to create such a large tidal response,"
said the paper's lead author Hamish Hay, a postdoctoral fellow at the
Jet Propulsion Laboratory in Pasadena, California, who did the research
when he was a graduate student in the University of Arizona Lunar and
Planetary Laboratory.

Understanding how the moons influence each other is important because it
can shed light on the evolution of the moon system as a whole. Jupiter
has nearly 80 moons, the four largest of which are Io, Europa, Ganymede
and Callisto.

"Maintaining subsurface oceans against freezing over geological times
requires a fine balance between internal heating and heat loss, and
yet we have several pieces of evidence that Europa, Ganymede, Callisto
and other moons should be ocean worlds," said co-author Antony Trinh,
a postdoctoral research fellow in the Lunar and Planetary Lab. "Io,
the moon closest to Jupiter, shows widespread volcanic activity,
another consequence of tidal heating, but at a higher intensity likely experienced by other terrestrial planets, like Earth, in their early
history. Ultimately, we want to understand the source of all this heat,
both for its influence on the evolution and habitability of the many
worlds across the solar system and beyond." Tidal Resonance


==========================================================================
The trick to tidal heating is a phenomenon called tidal resonance.

"Resonance creates loads more heating," Hay said. "Basically, if you
push any object or system and let go, it will wobble at its own natural frequency. If you keep on pushing the system at the right frequency,
those oscillations get bigger and bigger, just like when you're pushing
a swing. If you push the swing at the right time, it goes higher, but
get the timing wrong and the swing's motion is dampened." Each moon's
natural frequency depends on the depth of its ocean.

"These tidal resonances were known before this work, but only known
for tides due to Jupiter, which can only create this resonance effect
if the ocean is really thin (less than 300 meters or under 1,000 feet),
which is unlikely," Hay said. "When tidal forces act on a global ocean,
it creates a tidal wave on the surface that ends up propagating around
the equator with a certain frequency, or period." According to the researchers' model, Jupiter's influence alone can't create tides with
the right frequency to resonate with the moons because the moons' oceans
are thought to be too thick. It's only when the researchers added in
the gravitational influence of the other moons that they started to see
tidal forces approaching the natural frequencies of the moons.



==========================================================================
When the tides generated by other objects in Jupiter's moon system match
each moon's own resonant frequency, the moon begins to experience more
heating than that due to tides raised by Jupiter alone, and in the most
extreme cases, this could result in the melting of ice or rock internally.

For moons to experience tidal resonance, their oceans must be tens to
hundreds of kilometers -- at most a few hundred miles -- thick, which
is in range of scientists' current estimates. However, there are some
caveats to the researchers' findings.

Their model assumes that tidal resonances never get too extreme, Hay
said. He and his team want to return to this variable in the model and
see what happens when they lift that constraint.

Hay also is hoping that future studies will be able to infer the true
depth of the oceans within these moons.

This study was funded by NASA's Habitable Worlds program.


========================================================================== Story Source: Materials provided by University_of_Arizona. Original
written by Mikayla Mace.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Hamish C. F. C. Hay, Antony Trinh, Isamu Matsuyama. Powering
the Galilean
Satellites with Moon‐Moon Tides. Geophysical Research Letters,
2020; 47 (15) DOI: 10.1029/2020GL088317 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200910150236.htm

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