MIST
Magnetosphere, Ionosphere and Solar-Terrestrial
Discovery of H3+ and infrared aurora at Neptune with JWST
By Henrik Melin (Northumbria University)
The molecular ion H3+ is a significant component of the ionospheres of the giant planets. By observing the near-infrared emission from this ion we can remotely diagnose the physical conditions of this region. This layer of the atmosphere is an importance conduit for energy transfer between the space environment, magnetic field, and the atmosphere below, and it is in this region that magnetospheric auroral currents deposit energetic electrons that form enhanced temperatures and densities of H3+.
H3+ was discovered at Jupiter, Saturn, and Uranus over 30 years ago and a great number of studies have been able to characterise the processes that occur in the ionospheres of these planets. However, despite many attempts using telescopes on the ground, H3+ has never been observed from Neptune, in spite of models predicting it should be detectable, based on data from the 1989 Voyager 2 encounter.
The James Webb Space Telescope (JWST) is the most powerful telescope ever put into space, designed to observe the first galaxies formed in the early Universe. We can leverage this extraordinary sensitivity to explore our own cosmic backyard, by pointing the telescope at the giant planets. The first JWST observations of Neptune were taken in June 2023, and we were able to detect H3+ for the first time (yay!), as well as localised H3+ emissions about the magnetic pole. In other words, we were able to detect the ionosphere and aurora of Neptune for the first time, exactly 100 years after it was discovered at the Earth (Appleton & Barnett, 1925).
See publication for details:
Melin et al., (2025), Nat. Astro., doi: https://doi.org/10.1038/s41550-025-02507-9
Can XMM-Newton Be Used to Track Compositional Changes in the Solar Wind?
By Simona Nitti (University of Leicester)
Continuous monitoring of the solar wind ion composition is vital for understanding solar-terrestrial interactions, particularly through the study of Solar Wind Charge Exchange (SWCX) emission. SWCX produces soft X-rays (<2 keV) when highly charged solar wind ions (e.g., O7+, O8+, C6+) interact with neutral atoms. This emission is ubiquitous across the solar system, occurring wherever the solar wind encounters interstellar neutrals or interacts with planetary environments, including those of Earth, Mars, Venus, Jupiter, and Pluto.
In this study (https://doi.org/10.1029/2024JA033323), we investigated whether SWCX emission from Earth’s exosphere, observed by the XMM-Newton telescope, can be used to infer solar wind composition. By comparing spectral line intensities extracted from XMM data with ion abundance measurements from the ACE spacecraft at L1, we found that OVIII emission closely tracks O8+ abundances. In contrast, other ions involved in the SWCX process—such as O7+, C6+, C5+, and Mg11+—do not exhibit a consistent correlation between their abundance and X-ray emission.
To explore whether XMM data still encodes information about the solar wind state, we employed a Random Forest Classifier to predict solar wind types, following the classification scheme by Koutroumpa (2024). Incorporating XMM features alongside proton parameters significantly improved model performance, with a macro-averaged F1 score of 0.80 ± 0.06, compared to 0.55 when using proton data alone. Notably, XMM emission features ranked among the top five most important inputs. Moreover, XMM emission features ranked among the top five most important predictors. This suggests that, while individual ion abundances cannot currently be inferred directly from emission fluxes, XMM still provides valuable insight into the solar wind type, from which an average compositional profile may be inferred. This work is particularly timely given the degradation of the heavy ion spectrometer onboard the Advanced Composition Explorer (ACE), which has left the scientific community without reliable near-Earth ion composition measurements since 2011.
(a) SWCX periods ACE O8+/p (where p is proton density) 2D histograms, averaged over their occurrence between 2000 and 2009, in a (O7+/O6+)×(C6+/C5+) space, with black lines separating different solar wind types.
(b). Occurrence rate of ACE O8+/p for the Streamer (black), Outlier (red) wind and ICMEs (green).
(c) (d) Same as left plots but for OVIII ion line fluxes from the XMM SWCX data set.
See publication for details:
, , , , , , & (2024). Can XMM-Newton be used to track compositional changes in the solar wind? Journal of Geophysical Research: Space Physics, 129, e2024JA033323. https://doi.org/10.1029/2024JA033323
Announcement of New MIST Councillors.
We are very pleased to announce the following members of the community have been elected unopposed to MIST Council:
- Rosie Johnson (Aberystwyth University), MIST Councillor
- Matthew Brown (University of Birmingham), MIST Councillor
- Chiara Lazzeri (MSSL, UCL), Student Representative
Rosie, Matthew, and Chiara will begin their terms in July. This will coincide with Jasmine Kaur Sandhu, Beatriz Sanchez-Cano, and Sophie Maguire outgoing as Councillors.
The current composition of Council can be found on our website, and this will be amended in July to reflect this announcement (https://www.mist.ac.uk/community/mist-council).