Observation of Mercury's sodium tail using Fabry-Perot Interferometer

We observed sodium emission from Mercury's atmosphere using a Fabry-Perot Interferometer at Haleakala Observatory on June 14, 2006. The Fabry-Perot Interferometer was used as a wavelength-tunable filter. The spectra of the surface reflection were subtracted from the observed spectra because sodium emission is contaminated by the surface reflection of Mercury. The image obtained in our observation shows the sodium exosphere extended to the anti-solar direction. The lifetime of a sodium atom was estimated to be 1.6 × 104 to 1.9 × 105 s with an error by a factor of 3-4.