The Role of Electrons in Sputtering on Icy Moons

In our solar system, some icy bodies like Europa, Ganymede, and Callisto are fascinating because they might have atmospheres called exospheres. These exospheres are made up of different gases, including oxygen, which comes from a process called Sputtering. Sputtering occurs when energetic particles, like Electrons and ions, hit the surface of these icy bodies and knock off material. This article focuses on how electrons affect sputtering on HO-ice and its implications for these icy moons.

#Sputtering and Its Importance

Sputtering is a key mechanism that can form exospheres around planetary bodies. When particles like electrons and ions collide with the surface, they can cause atoms or molecules to be ejected. This is important for understanding the atmospheres of moons and planets that do not have thick atmospheres to protect them. In the case of icy bodies, sputtering can lead to the production of gases that may contribute to their overall atmosphere.

#Electrons and Their Role

Electrons are one type of particle that can sputter material from icy surfaces. Previous research mainly focused on ions because they seemed more potent in causing sputtering. However, electrons represent a significant portion of the total energy and particles striking surfaces like Europa. It turns out that even though individual electrons might cause less sputtering than ions, their higher flux can make them important players in creating exospheres.

#Research on HO-Ice

To investigate the effect of electrons on sputtering from HO-ice, we conducted experiments to measure how much material is ejected when HO-ice is bombarded with electrons. These experiments looked at how different electron energies (from 0.75 to 10 keV) and temperatures (from 15 to 124.5 K) influenced sputtering yields.

#Key Findings

1. Energy Dependence: We found that as the energy of the electrons decreased, the total amount of sputtered material increased. This means that lower-energy electrons are more effective in sputtering HO-ice than higher-energy ones.

2. Temperature Effects: The sputtering yields also change with temperature. At temperatures below 60 K, the sputtered yield remained relatively constant. However, once the temperature exceeded 60 K, the sputtering yields increased dramatically.

3. Composition of Sputtered Material: The composition of the material that gets ejected depends on the energy of the electrons. At lower energies, a large portion of the sputtered material was HO, while at higher energy levels, the contribution of HO decreased significantly.

#Comparing With Other Studies

When comparing our findings with other studies on ion-induced sputtering, we noticed some significant differences. Previous studies showed that ion sputtering has a different behavior than electron sputtering, particularly regarding how the composition of ejected material varies with energy.

#Implications for Europa

Applying our findings to Europa, we estimate that electron-induced sputtering could contribute significantly to the production of oxygen in its exosphere. Our calculations suggest that the contribution from electrons may be on par with that from all ion types combined. This indicates that electrons play a crucial role in shaping the atmosphere of Europa.

#Ganymede and Callisto

In contrast to Europa, the sputtering of oxygen from Ganymede and Callisto appears to be mainly dominated by ion interactions. Still, electrons likely provide a smaller but important contribution. Understanding how these processes differ across the Galilean moons can offer insights into their individual atmospheres and potential for habitability.

#Experimental Setup

Our experiments were performed in a controlled environment using a stainless steel vacuum chamber. This setup allowed us to create low-pressure conditions necessary for studying the sputtering of HO-ice. We used a special device to freeze HO-ice and maintained precise temperatures during the experiments.

#Measuring Sputtering Yields

To quantify the amount of material ejected during electron bombardment, we employed two main techniques: microbalance gravimetry and mass spectrometry. These methods helped us measure the mass loss of the ice due to sputtering and analyze the gases released during the process.

#Data Analysis

In our analysis, we focused primarily on the partial pressure of oxygen ejected during the experiments. By tracking how this pressure changed during electron irradiation, we were able to derive meaningful data on how much material was being sputtered.

#Sputtering Results

We compiled a comprehensive list of sputtering yields across various temperatures and electron energies. The results confirm that sputtering is a complex process influenced by both energy and temperature. Our findings will contribute to more accurate models of sputtering and their implications for the icy moons of Jupiter.

#Theoretical Models and Future Work

We also contrasted our experimental data with theoretical sputtering models that used parameters derived mainly from ion data. Our new findings suggest that these models may require adjustments to account for the unique effects of electrons.

#Conclusions

The research underscores the importance of considering electrons in models of sputtering and atmosphere production on icy bodies. While ions have been the focus of many studies, it is evident that electrons also have a significant impact. Future research should continue to explore the effects of electron sputtering, especially as we aim to understand the atmospheres of moons like Europa, Ganymede, and Callisto.

As our understanding of these processes deepens, we can better assess the potential for life and the conditions on these fascinating celestial bodies. This study highlights the need for ongoing exploration and experimentation to unravel the complexities of sputtering and its role in shaping the universe around us.