Comet was released in 1974 by the USDA breeding program, only two years after Cascade, and it was among the very first American hops bred with high alpha acid specifically as a breeding goal rather than as an incidental trait. It didn't achieve Cascade's lasting commercial success and fell out of wide use for decades, but it's seen a genuine resurgence in modern brewing for a character that reads distinctly different from the more polished varieties that came after it.
Comet's 9-12% alpha acid is high enough to anchor a real bittering charge rather than serve aroma duty alone, and its grapefruit and black currant profile carries an additional pungent, "catty" note — a slightly musky, ammonia-adjacent quality some brewers find off-putting in isolation and others specifically seek out for the sharp, aggressive edge it lends a hop-forward beer. That catty character is a defining, polarizing trait rather than a flaw; it's simply not to every palate. The IBU calculator handles the arithmetic for a bittering or late addition either way.
Cascade is the closer substitute for the citrus side of Comet's profile without the pungent edge, while Centennial offers a higher-alpha alternative in the same general citrus-forward American family. Modern American pale ale and IPA use Comet as a deliberate, slightly retro choice for brewers wanting a rougher-edged citrus character than the smoother varieties bred since. Comet's alpha floor sits above Cascade's ceiling entirely, while Centennial's range overlaps it closely, making Centennial the more realistic substitute of the two for matching bitterness at the same weight.