If a State wishes to authorize capital punishment it has a constitutional responsibility to tailor and apply its law in a manner that avoids the arbitrary and capricious infliction of the death penalty. Part of a State's responsibility in this regard is to define the crimes for which death may be the sentence in a way that obviates standardless sentencing discretion. It must channel the sentencer's discretion by clear and objective standards that provide specific and detailed guidance, and that make rationally reviewable the process for imposing a sentence of death. "A State's definitions of its aggravating circumstances those circumstances that make a criminal defendant 'eligible' for the death penalty--therefore play a significant role in channeling the sentencer's discretion." To satisfy constitutional mandates, an aggravating circumstance must meet two basic requirements. First, it "must genuinely narrow the class of persons eligible for the death penalty and must reasonably justify the imposition of a more severe sentence on the defendant compared to others found guilty of murder." Second, "the aggravating circumstance may not be unconstitutionally vague." A challenged provision is impermissibly vague when it fails to adequately inform juries what they must find to impose the death penalty and as a result leaves them and appellate courts with open-ended discretion.