This plot shows the intensity of emission of light associated with sodium
atoms in the vicinity of Mercury. The observations were made with the
Ultraviolet and Visible Spectrometer (UVVS) section of the Mercury
Atmospheric and Surface Composition Spectrometer (MASCS). The intensity
(up to 40 kiloRayleighs) indicates the relative abundance of material, in
this case sodium atoms, along the observational line of sight back to the
spacecraft. While sodium from Mercury has been observed with Earth-based
telescopes, this is the highest-spatial-resolution image ever made. The
geometry and observing circumstances have to be disentangled to infer the
true spatial distribution, but the observations do confirm a north-south
asymmetry that has previously been observed in ground-based sodium images.
The sodium emission is at 589 nm (in the visible part of the spectrum and
the same wavelength, or color, as in sodium lamps and street lights on
Earth). Because sodium atoms have intense emission, they are easy to
detect, and this makes sodium a good tracer for other volatile elements in
Mercury's exosphere.
These images are from MESSENGER, a NASA Discovery mission to conduct the
first orbital study of the innermost planet, Mercury. For information
regarding the use of images, see the MESSENGER image use policy.
