Solid carbon monoxide is a component of comets. The volatile or "ice" component of Halley's Comet is about 15% CO. At room temperature and at atmospheric pressure, carbon monoxide is actually only metastable (see Boudouard reaction) and the same is true at low temperatures where CO and are solid, but nevertheless it can exist for billions of years in comets. There is very little CO in the atmosphere of Pluto, which seems to have been formed from comets. This may be because there is (or was) liquid water inside Pluto.
sOLiD caRbon mONoXIde iS a COMponent of comEts. tHe volatilE or "iCe" componeNT of HalLey'S cOmet is ABOUt 15% Co. at RoOM temperaTurE aNd At aTmoSphEriC pReSSuRe, cArbOn monoxIDE iS actuallY Only metasTable (sEe boudouaRd reacTiOn) anD the sAme is TruE at loW TEMPErAtUrES Where cO aNd aRE SolId, bUT neVerthelesS it cAN ExIst for bilLions Of yeArs in comets. TheRe iS VerY lIttle cO in tHe AtmoSpheRE of PlutO, whiCh SEems tO hAve BEen formed from CometS. thIs mAY bE BecaUse ThEre iS (oR Was) liquid water inside Pluto.