Jupiter’s moons can heat each other through tidal resonance

Jupiter’s four largest moons in order of distance from Jupiter: Io, Europa, Ganymede and Callisto. Sincerely: NASA / JPL / DLR

Gravitational push and pull by JupiterGas giants alone can account for more warming than Jupiter.

Jupiter’s moons are hot.

Well, in order to be so far away from the sun, they need to be as warm as possible. In a process called tidal heating, gravity tugs from Jupiter’s moons and the planet itself squashes the moon enough to stretch and warm them. As a result, some icy moons warm inward to host oceans of liquid water, and in the case of the rocky moon IO, tidal heating melts the rock in the magma.

Researchers previously believed that the gas giant Jupiter was responsible for most of the tidal ebb associated with the liquid interiors of the moon, but a new study appeared. Geophysical research paper It was found that the Moon – Moon interaction may be more responsible than Jupiter than the Moon alone.

“This is surprising because the moons are much smaller than Jupiter. You wouldn’t expect them to be able to respond to such a huge tide, ”said Hamish Hay, lead author of a postdoctoral fellow paper at the Jet Propulsion Laboratory in Pasadena, California, that he did research when he was a graduate student. University of Arizona Lunar and Planetary Laboratory.

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

“To maintain subsurface oceans against freezing over geological time requires a fine balance between internal heating and heat loss, and yet we have many pieces of evidence that Europa, Ganymede, Callisto and other moons Must Be the World of the Seas, ”co-authored Antony Trinh, a Postdoctoral Research Fellow at the Lunar and Planetary Lab. “IO, the Galilean moon closest to Jupiter, shows another consequence of widespread volcanic activity, tidal heating, but at higher intensities experienced by other terrestrial planets such as Earth, in its early history. Finally, we cross the solar system and Beyond that, many want to understand the source of all this heat, for its development on the world and its impact on habitat potential. ”

Tidal resonance

The speed of tidal heating is a phenomenon known as tidal resonance.

“The resonant load creates more heating,” Hay said. “Basically, if you push an object or system and let go, it will wobble at its natural frequency. If you keep moving the system at the correct frequency, those oscillations become larger and larger, as you are pushing a swing. If you push the swing at the right time, it becomes longer, but the timing goes wrong and the swing speed decreases. ”

The natural frequency of each moon depends on the depth of its ocean.

“These tidal resonances were known before this work, but are known only for tides due to the jupiter, which can only cause this resonance effect if the ocean is indeed thin (less than 300 meters or 1,000 feet Less), which is unlikely, ”said Haye. “When tidal forces act on a global ocean, it creates a tidal wave on the surface that ends the propagation around the equator with a fixed frequency or duration.”

According to the researchers’ model, the effect of Jupiter cannot produce tides with the correct frequency to resonate with the Moon alone because the Moon’s oceans are considered too thick. It is only when researchers have added to the gravitational effects of other moons that they started moving tidal forces closer to the natural frequencies of the moon.

When the tides generated by other objects in Jupiter’s lunar system match each moon’s own resonant frequency, the moon begins to experience even more heat due to the tides raised by Jupiter alone, and in the most extreme cases, it Melting of ice can result. 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 the range of current estimates by scientists. However, there are some caveats to the researchers’ findings.

His model assumed that tidal resonance is never overdone, Hay said. He and his team want to return to this variable in the model and see what happens when they lift that constraint.

Haye is also hoping that future studies will be able to estimate the actual depth of the oceans within these moons.

Reference: Hamish CFC, “The Power of Gallian Satellites with the Moon Moon” by Antony Trinih and Isamu Matsuyama, 19 July 2020 Geophysical research paper.
DOI: 10.1029 / 2020GL088317

This study was funded by NASAHazel Worlds Program.