Predicting CO Cameron-band auroral emission at Venus using VEx Observations

Auroral emissions have been observed (partially) on magnetized planets, such as Earth, Jupiter, and Mars, illuminating the plasma processes mostly related to planetary intrinsic fields. Aurorae have also been reported to occur at Venus, an unmagnetized planet, by the Pioneer Venus Orbiter (PVO). Previous modeling efforts suggest that the observed CO Cameron-band auroral emissions are mainly produced by electrons at 10s-100s of electron volts (eV) impacting the Venus nightside upper atmosphere. Yet, little was discussed in previous studies regarding how these source electrons access the atmosphere. By applying a linear relation, this study predicts the possible CO Cameron-band emission brightness at Venus using electron observations from Venus Express (VEx). Our results suggest that to produce the PVO observations, electron acceleration is not required as in the case of discrete aurorae at magnetized planets; rather, the magnetic access of precipitating electrons to the lower atmosphere is the more limiting factor for auroral occurrence. This study helps better understand how aurorae can occur at an unmagnetized planet, in contrast to magnetized planets. It also has implications for future Venus mission design: auroral imaging can serve as a remote sensing tool to characterize the magnetization state of the Venus nightside atmosphere.