Figure 3.

Estimates of the accretion times of the chondrite parent bodies (modified after [72]). All the chondrites have avoided melting, but they experienced sufficient lithification as a result of metamorphism and/or aqueous alteration to be robust enough to survive impacts and atmospheric entry. Hence, the chondrites must have formed in a window of time between when there was not quite enough short-lived radioactivity to melt and differentiate planetesimals, and when there was not enough radioactivity to even melt water ice. With the exception of the highly reduced enstatite chondrites (E) and possibly the COs, all the chondrites accreted at least some water, presumably as ice, implying accretion temperatures that were below the sublimation temperature of water ice in the nebula (150–170 K). (Online version in colour.)