Infrared excess One of the early results from the Infrared Astronomy Satellite (IRAS) was the discovery of excess infrared flux coming from Vega, beyond what would be expected from the star alone. This excess was measured at wavelengths of 25, 60 and , and came from within an angular radius of () centered on the star. At the measured distance of Vega, this corresponded to an actual radius of (AU), where an AU is the average radius of the Earth's orbit around the Sun. It was proposed that this radiation came from a field of orbiting particles with a dimension on the order of a millimetre, as anything smaller would eventually be removed from the system by radiation pressure or drawn into the star by means of Poynting–Robertson drag. The latter is the result of radiation pressure creating an effective force that opposes the orbital motion of a dust particle, causing it to spiral inward. This effect is most pronounced for tiny particles that are closer to the star.
InfRArEd exCEss one oF the earLY rEsulTs froM the iNfRarEd AstRoNOmY saTellIte (iRas) wAS thE discovEry of eXcess infRARed FLux coMing fRom VEGa, beyOnd What Would Be expecteD from the star aLonE. this excess WaS meaSureD aT waVeleNgThs Of 25, 60 and , And Came from wIthin aN anGular radiuS of () centered on thE star. at the Measured disTancE oF vEga, THis corresPOndEd To an actUal radIus of (au), wHeRe an au Is The average radIUS Of the earTh'S ORbit ArOunD the sUN. it wAs prOPosed that ThiS RadiAtion caMe FroM a FIEld of oRBItIng paRtiCLes With a dImeNSion oN ThE order of A millimeTRe, As anYthing smalleR wOulD evENtuAllY be removeD from thE syStEM by radIation PReSsurE or DraWN into the sTar By Means oF poyNtiNg–robErtSON DRag. the LatteR is tHe rEsult of raDiaTIoN preSsuRE creatinG An eFfectiVE fOrce thAt OpPoSes ThE Orbital motiON Of A dUst PartiClE, cAusIng It to SpiRal inwArd. THis EFFect is moSt pronouNCeD for tIny pArTicleS that are cLoSER to the stAR.