Comet strike could deliver ingredients for life to Europa's ocean

The comet doesn't have to pierce entirely through the icy moon shell.
Ayesha Gulzar
An artist's concept of a comet or asteroid impact on Jupiter's moon Europa.
An artist's concept of a comet or asteroid impact on Jupiter's moon Europa.

NASA/JPL-Caltech 

Jupiter's moon, Europa, is believed to have a vast ocean of liquid water beneath its icy surface. This ocean is considered one of the most promising places in the solar system to search for signs of life outside Earth.

Now researchers from the University of Texas have found that comet strikes could help transport necessary ingredients for life on the moon's surface to its hidden ocean, where it could help sustain any life that may be present in the dark. The passage of ingredients is possible even if the comet doesn't pierce the gas giant's icy moon shell, according to an institutional press release.

A computer simulation of the comet's impact

The team developed a computer model to observe what happens after a comet or asteroid strikes the ice shell, which is estimated to be tens of kilometers thick.

The model shows that an asteroid or comet penetrating only halfway through Europa's ice shell will create a massive meltwater that will sink through the rest of the ice. According to the study, more than 40 percent of the water will reach the ocean, bringing oxidants - a class of chemicals required for life - from the surface to the ocean, where they can support any potential life in the sheltered waters.

"Once you get enough water, you're just going to sink," said lead author and doctoral student Evan Carnahan. "It's like the Titanic times 10."

Scientists have proposed impacts as a means to transport oxidants on Europa, but they assumed the strikes would have to break through the ice. This study is important because it suggests that a much larger range of impacts can do the job, said co-author Marc Hesse, a professor at the UT Jackson School of Geosciences Department of Geological Sciences.

"This increases the probability that you would have the necessary chemical ingredients for life," said Hesse.

Comet strike could deliver ingredients for life to Europa's ocean
Tyre, a large impact crater on Europa.

Potential habitability on Europa

One of the goals of NASA's Europa Clipper mission, which will launch in October 2024, is to collect data that can help test whether oxidants can reach the moon's underground ocean from the satellite's surface. The mission will conduct a detailed exploration of Europa and investigate whether the icy moon can support life.

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However, at the moment, impacts from comets and asteroids are thought to be one of the most likely mechanisms for the origin of life on Europa. Scientists have already discovered dozens of craters on its surface. Many have a distinct rippled appearance that suggests frozen meltwater and post-impact motion beneath the crater.

While the study has focused on Europa, it has implications for other icy worlds with subsurface oceans, such as Saturn's moon, Titan.

"In the case of Titan, this is very important because Titan has a thick ice crust — thicker than Europa's. We're really interested in the application of this study," said Rosaly Lopes, the directorate scientist for the Planetary Science Directorate at NASA's Jet Propulsion Laboratory (JPL).

The study was published in Geophysical Research Letters.

Abstract

Impacts into icy bodies often generate near-surface melt chambers and thermal perturbations that soften the ice. We explore the post-impact evolution of non-penetrating impacts into Europa's ice shell. Simulations of viscous ice deformation show that dense impact melts founder before refreezing. If the transient cavity depth exceeds half the ice shell thickness, over 40% of the impact melt drains into the underlying ocean. Drainage of impact melts from the near-surface to the ocean occurs on timescales of 103–104 years. The drainage of melts to the ocean occurs for all plausible ice shell thicknesses and ice viscosities, suggesting that melt foundering is a natural consequence of impacts on icy worlds. Post-impact viscous deformation is an important process on icy worlds that affects cryovolcanism, likely modifies crater morphology, creates porous columns through the ice for surface-to-ocean exchange, and may supply the oxidants required for habitability to subsurface oceans.