14 October 2015

New research shows impacts from comets or asteroids could have created Europa’s chaos terrain

Posted by llipuma

By Mary Dettloff

Jupiter's moon Europa has an ocean of liquid water beneath its frozen surface. Impactors, such as comets or asteroids, could have breached the icy surface and penetrated the water below, creating the moon’s mysterious chaos terrain. Credit: NASA-JPL

Jupiter’s moon Europa has an ocean of liquid water beneath its frozen surface. Impactors, such as comets or asteroids, could have breached the icy surface and penetrated the water below, creating the moon’s mysterious chaos terrain.
Credit: NASA-JPL

What began as Williams College students requesting a new course on planets and moons nearly 12 years ago has now culminated in a new research paper showing that impactors, such as comets or asteroids, can penetrate the frozen surface of Jupiter’s moon Europa. The paper has been accepted for publication in the Journal of Geophysical Research: Planets, a publication of the American Geophysical Union.

Since 2004, undergraduate students led by Rónadh Cox, professor of geoscience, have studied the ice-covered surface of Europa, trying to understand the origins of its chaos terrain: areas that look like crustal breaches, with icebergs embedded in frozen slush. Cox’s students explored various hypotheses for how these features might have formed, focusing on the possible role of impacts.

In 2009, student Aaron Bauer, a computer science major, took Cox’s planetary tutorial course and became fascinated with this question. Bauer taught himself the programming language Fortran so that he could run numerical simulations to test the hypothesis that comets or asteroids had breached Europa’s ice, exposing the underlying liquid ocean and possibly forming chaos terrain.

The modeling showed that ice penetration is possible for a range of situations.  For example, a half-kilometer diameter comet is capable of puncturing five kilometers of ice, whereas a five-kilometer comet could penetrate 40 kilometers of ice.  The research also showed that no matter Europa’s ice thickness, there is an impactor size with geologically reasonable recurrence that it is likely to breach it. This means that it is likely that Europa’s ice-covered oceans were exposed often in the deep past, as well as in recent geological time.

Such penetrations would form conduits allowing the transfer of astrobiological material between the surface and the underlying ocean. Whether or not this is an important process on Europa – or whether it occurs at all – has not been established, but it could be important for Europa’s potential to harbor life.

“How Europa’s sub-ice surface ocean communicates with the surface, can mass and energy be transferred from the exterior to the liquid beneath and how thick the ice barrier is have been questions at the forefront of research since the Galileo data in the early 2000s revealed the probable existence of a liquid water layer,” Cox said. “The research conducted by students about the breaches that occur in the ice could contribute to a better understanding of how they are caused.”

The paper, co-authored by Bauer and Cox, will be presented at a Geological Society of America meeting in November.

– Mary Dettloff is the director of media relations at Williams College.