In 2014, the organic compound ethyl mercaptan (CH₃CH₂SH) (also known as ethanethiol) was identified in existing survey data by Kolesniková et al. using their new experimental data for the compound. Tercero et al. surveyed several spectral windows toward Orion KL using the IRAM 30m radiotelecope. Over 14 000 spectral lines were detected in the survey, of which about 4000 could not be assigned at the time to known molecules. New laboratory characterization of molecules such as ethyl mercaptan has led to assigning many of these unknown lines.

Ethyl mercaptan has two types of structures, called rotamers, as shown in the figure to the right. As the -SH thiol group part of the molecule rotates around through 360 degrees, it passes through three minima. The most stable of these are two equivalent, mirror image gauche conformers. The final, less stable minimum is a trans conformer, that occurs when the H on SH faces away from the C–C–S backbone of the molecule. Spectral signatures of both the gauche and trans conformers were found by the study described above, but there is better evidence that the gauche conformer is present in Orion KL than the trans one. 77 lines in the survey match the spectrum of gauche ethyl mercaptan.

Ethyl mercaptan's chemical cousin, methyl mercaptan, was first reported in space in 1979. Both compounds are added to combustible hydrocarbons as leak detectors due to their strong and distinctive odors; ethyl mercaptan is the primary odorant added to propane and butane.