In 2008 the "MESSENGER" probe's Fast Imaging Plasma Spectrometer (FIPS) discovered several molecular and different ions in the vicinity of Mercury, including H2O+ (ionized water vapor) and H2S+ (ionized hydrogen sulfide). Their abundances relative to sodium are about 0.2 and 0.7, respectively. Other ions such as H3O+ (hydronium), OH (hydroxyl), O2+ and Si+ are present as well. During its 2009 flyby, the Ultraviolet and Visible Spectrometer (UVVS) channel of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) on board the "MESSENGER" spacecraft first revealed the presence of magnesium in the Mercurian exosphere. The near-surface abundance of this newly detected constituent is roughly comparable to that of sodium.