In 2012, the mercapto radical, SH, became one of the first detections of a previously unknown interstellar molecule to be made with the new SOFIA airborne observatory. Neufeld and co-workers identified it in the giant molecular cloud W49A via a rotational transition in the infrared.

The initial detection of SH in an astrophysical source was reported in 2000 by Yamamura et al. They found the species in the atmosphere of the S-type star R Andromedae, via its ro-vibrational spectrum. A detection of SH on the atmosphere of our own sun was reported in 2000 by Berdyugina & Livingston using UV transitions. SH is also known as sulfur monohydride and as the sulfanyl radical. The singly-occupied orbital is shown to the right. It very much resembles a S 3p orbital.