Coordinated campaign of ground-based observations of Mercury’s exosphere in 2021

International audienceIn October-November 2021 a ground-based campaign measuring the exosphere of Mercury took place with participation from four different facilities in the US and in the Canary Islands.In daylight, the THEMIS and Dunn solar telescopes mapped sodium and potassium at high spectral resolution. In twilight, Mercury’s Na tail was measured with a long-slit spectrograph at the Apache Point 3.5m telescope between 3-15 Mercury radii, and with the IoIO coronagraphic imager out to more than 100 Mercury radii.Each of these facilities has specific capabilities and their synoptic use can provide global coverage of the morphology of the exosphere of Mercury:• Daylight observing is a means to regularly measure the exosphere above the disk of Mercury, and the new adaptive optics system at THEMIS and Rapid Imaging Planetary Spectrograph at Dunn will help facilitate such observations.• Measurements of the escaping Na tail constrain the budget of sources and sinks in the exosphere and help identify transient enhancements from ion sputtering or meteor impacts, as with higher energy such enhancements preferentially escape.We will show the results obtained up to now, with a special focus on the two days in which all four facilities were observing at the same time