Two different articles, one to be published in the journal “Icarus” and one published in the journal “Monthly Notices of the Royal Astronomical Society”, describe different aspects of a study that offers a new model to describe the tidal effects that might cause fractures on the surface of icy moons. According to a University of Rochester team led by Alice Quillen the tidal effects of a close encounter could explain very extensive fractures.

These moons show what is called brittle elastic behavior, characterized by the fact that there’s little plastic deformation between an elastic behavior and the production of fractures. Alice Quillen used as a comparison a toy called Silly Putty that bounces if it’s dropped on the floor but gets torn apart if it’s pushed hard.

To test if such behavior could generate large fractures in icy moons, Alice Quillen and her collaborators created computer graphics models. They had to take into account the different characteristics of the bodies involved and the interior of each moon was modeled as if it was composed of many bodies connected by springs.

Technically this type of problem is called N-body problem and is addressed in various scientific disciplines. In the field of astronomy it’s often used to study the gravitational effects on stars and planets but it’s the first time that is used to create a model of a celestial body’s interior.

The application of the N-body problem to various moons allowed to simulate the intensity of tidal forces in a close encounter with another celestial body. That could be the planet the moon is orbiting but even more it could happen a few billion years ago, when the situation in the solar system was chaotic. Celestial bodies of various sizes could have close encounters with various consequences.

The simulations showed that if the gravitational intensity has certain values an icy surface may be fractured. In the article on “Monthly Notices of the Royal Astronomical Society” the researchers showed that the models are consistent with the rate at which moons spin up or down when orbiting another.

According to the results reported in the article to be published in “Icarus” tidal forces can create fractures such as those observed on various moons: Charon (Pluto), Dione and Tethys (Saturn) and Ariel (Uranus). In particular the huge fracture on the surface of Charon puzzled scientists because the only gravitational influence of Pluto is far too weak to create it.

This theory is interesting and the model could be applied even to Mars but takes into account only some characteristics of the moons that were examined. Additional checks that take account of pre-existing conditions, such as if there were already fractures or more complex gravitational influences, are needed. For sure it offers clues to be taken into account in the study of the interactions between celestial bodies.