According to current theory, comets are a bit like cosmic baby birds, delivering life-bearing ingredients to a young Earth billions of years ago.
Comets may play a similar role in transporting other life-giving compounds to nearby planets, allowing reactive chemicals — known as oxidants — to pass through the icy shell and into Jupiter, new research by scientists at the University of Texas, Caltech and William College finds The oceans of the satellite Europa.
Even if the comet doesn’t penetrate the ice completely, the force of the impact could help transport oxidants from Europa’s surface to the ocean below. Computer models show that an asteroid or comet impact only needs to penetrate halfway through the 15-25 km thick ice layer to create huge melting ice holes that allow the comet to continue to pass through the ice layer.
Even the solar system faces enormous challenges when it comes to the search for life beyond Earth. No planet is as unique as Earth, but some worlds may have the environmental conditions that Earth can support life, one being Europa, along with other icy moons, Saturn and Titan.
These planets are far from the sun and well outside the habitable zone. The cold, combined with the extreme darkness of the ocean’s depths, meant that life lacked the photosynthetic food webs that most life on Earth relies on. While some life does thrive in Earth’s light-starved depths, clustered around hydrothermal vents that spew heat and chemicals from the seafloor are entire ecosystems based on chemosynthesis—using chemical reactions to generate energy instead of sunlight.
Europa believes that there are hydrothermal vents, and the core heat source is provided by the interaction between the satellite core and Jupiter’s gravity, which generates tension and compression. But scientists think any carbon-based life would likely need oxidizing agents to survive. These oxidants are produced by solar radiation hitting Europa’s surface, but this is of limited use to the subsurface marine ecosystem separated from the surface by a thick ice crust.
▲ The huge corrugated impact crater on the surface of Europa. (Source: NASA/JPL/DLR)
One potential transport mechanism is comet and asteroid impacts, which generate enormous heat and melt ice, sinking oxidizers. Europa does have some impact craters, though not many, because tectonic activity created ice plumes and volcanoes that covered them for a short time. Still, satellites are no strangers to bombardment, and those identified impact craters show concentric ripples, indicating significant melting following the impact, followed by subsurface movement.
To determine whether these impacts were enough to deliver oxidizer, Carnahan and his team simulated throwing rocks at Europa to see what happens after the impact. Melting ice that is denser than the surrounding ice does not create a shallow layer of ice water that then refreezes, but sinks downward.
According to the team’s simulation, if the impact depth reaches half of Europa’s ice shell, 40% of the melted ice will eventually sink into the subsurface ocean. This has implications not just for Europa, but for other icy worlds with subsurface oceans.
The paper reads: “This study demonstrates that subsidence from impact melt ice is a viable, robust, and potentially widespread mechanism for transporting surface material to Europa’s subsurface ocean. While this study focused on Europa, it’s likely to happen on other icy worlds like Europa, such as Titan.
The research was published in Geophysical Research Letters.
(This article is reproduced with the authorization of Taipei Planetarium; source of the first image: JPL)
