Halley’s Comet, 1910
What was predicted: When Halley’s Comet reappeared in 1910, the Chicago Yerkes Observatory made the poorly calculated decision to announce that it had detected a poisonous gas in the comet’s tail. The New York Times added fuel to the fire by quoting a French astronomer as saying this gas “would impregnate that atmosphere and possibly snuff out all life on the planet.” Panic ensued, gas masks were purchased, and people began loading up on "comet pills," [emphasis ours] which promised to counter the effects of the noxious gas. In an attempt to keep the fumes at bay, homeowners placed pieces of paper over their locks.
What actually happened: The planet remained undisturbed. Once the comet had passed, The Chicago Tribune announced to readers, “We’re still here.”