Bark splitting is common on maples. It's most likely a frost crack, in which longitudinal cracks develop on the trunk of trees facing south or southeast as bark and wood expand, then contract, in response to big temperature changes between day and night (bark absorbs the sun's heat, then the temperature plummets after sunset).These cracks usually heal over, entirely or partly, in the following growing season. For more information contact your local county UW-Extension office (https://counties.uwex.edu/).