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“Unfortunately in the entire mission we saw no oxygen in the Mercury exosphere, in contrast with what Mariner 10 reported,” Rosemary Killen, XXX, told Space.com by email. Estimates based on Mariner’s observations suggested that oxygen made up 42 percent of the tiny planet’s atmosphere.
“We think they gave a generous upper limit,” Killen said.
The atmosphere is filled instead with sodium, magnesium, and calcium, which are spread across the planet. Traces of hydrogen, helium, and potassium were also detected. Before the newest spacecraft arrived, scientists thought that solar radiation carried material kicked up on the sun-lit side by solar wind and radiation over to the night side, a process known as ion sputtering. According to MESSENGER co-investigator William McClintock, a senior scientist at the University of Colorado, Boulder, MESSENGER’s observations reveal a variety of interactions affecting the movement of the atoms.
“They show that distinctly different source and loss processes control the populations of the major constituents,” McClintock said in a statement.
The main factor instead appears to be photon-stimulated desorption (PSD), a where photons release sodium.
According to Killen’s research, sodium, calcium, and magnesium are each released by different processes and more likely to collide with the planet’s surface than with each other.
There is almost no gas, no water vapor, no oxygen or other common elements we associate with an "atmosphere’.
The other article I provided supports the same.