[nigwil_]

Subtitle is a better heading and less border-line click-bait:

"Trace Gas Orbiter spacecraft did not find the gas in red planet’s atmosphere during its first months of operation"

[KnightOfWords]

Flummoxed is pretty fair in this case. The expectation is that any methane released into the Martian atmosphere should persist on long timescales. Either there is a unknown process which scrubs it quickly or previous measurements were in error.