3 upvotes, 1 direct replies (showing 1)
View submission: Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science
Oh! A question I can answer!
Because Mercury has a small magnetosphere (and almost non-existent atmosphere), it is highly sensitive to solar wind changes, and processes happen very quickly (sorry, my source for this is a book I own. But there are a lot of papers that mention it, like this one by Slavin et al., 2014[1]). This includes changes in the levels of plasma precipitation, which is when solar wind plasma impacts on the surface, and is the source of the exospheric sodium which then produces a tail. So the magnetosphere itself changes dramatically based on solar activity, and on very short timescales.
1: https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2014JA020319
The sodium tail typically observed is neutral sodium, which is not as sensitive to solar wind changes. However, it does change with distance from the Sun (which, for Mercury, is effectively season) as shown in both ground-based data (Baumgardner et al., 2008[2] and Schmidt et al., 2010[3] are two of many paper discussing variability in the tail) and MESSENGER data (Jasinski et al., 2021[4]). So, if you consider distance from the sun/season as a type of "solar activity", then yes! In terms of solar cycle, it seems to be more complicated. Page 26 of Millilo et al., 2020[5] says that the scientific community is a bit divided on what the major driver of the neutral exosphere is (whether photons, plasma precipitation causing sputtering, thermal, etc). It's definitely a combination of all of them, so solar activity like CMEs does have an effect. The Millilo paper also contains a ton of citations to other papers if you'd like more info.
2: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2007GL032337
3: https://www.sciencedirect.com/science/article/abs/pii/S0019103509004333?via%3Dihub
4: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL092980
5: https://www.diva-portal.org/smash/get/diva2:1470767/FULLTEXT01.pdf
Ultimately, this may be something BepiColombo can help us understand. With two spacecraft, we will have multipoint measurements inside the planet's magnetosphere, which can tell us a lot about what processes are going on, and we will be able to observe both neutral and ionized sodium in situ.
Comment by tjernobyl at 28/04/2023 at 15:57 UTC
1 upvotes, 1 direct replies
Thank you for an excellent response, you've started me on a new journey of learning!