(a) Candidate found in HAT-P-39. See Figure 4 and the text for an explanation of the panels. Five emission lines having different intensities but equal wavelength spacing are apparent to the eye in the reduced spectrum (top panel). A zoom-in (second panel) shows three of those emission lines. The emission fills the spatial direction, albeit faintly (third panel). This series of emission lines is apparently unresolved emission from a laser or oscillator on Earth, the light subtending a large enough solid angle to fill the spectrometer slit. (b) A further zoomed-in view of the same feature in Figure 11(a), plotted on a log scale to enhance the contrast and exhibit the line’s spatial extent spanning the entire entrance slit. The diagonal line on the left is yet another glancing particle track.