Although there was a pronouncement by NASA during the mission saying that the Viking lander results did not demonstrate conclusive biosignatures in soils at the two landing sites, the test results and their limitations are still under assessment. The validity of the positive 'Labeled Release' (LR) results hinged entirely on the absence of an oxidative agent in the Martian soil, but one was later discovered by the Phoenix lander in the form of perchlorate salts. It has been proposed that organic compounds could have been present in the soil analyzed by both "Viking 1" and "Viking 2", but remained unnoticed due to the presence of perchlorate, as detected by Phoenix in 2008. Researchers found that perchlorate will destroy organics when heated and will produce chloromethane and dichloromethane, the identical chlorine compounds discovered by both Viking landers when they performed the same tests on Mars.