▁emission ▁is ▁expected ▁from ▁astronom ical ▁objects ▁that ▁contain ▁extremely ▁hot ▁g ases ▁at ▁temper atures ▁from ▁about ▁a ▁million ▁k el vin ▁( K ) ▁to ▁hundreds ▁of ▁millions ▁of ▁k el vin ▁( M K ). ▁Moreover , ▁the ▁maintenance ▁of ▁the ▁E - layer ▁of ▁ion ized ▁gas ▁high ▁in ▁the ▁Earth ' s ▁Th erm os phere ▁also ▁suggested ▁a ▁strong ▁extr ater rest rial ▁source ▁of ▁X - ray s . ▁Although ▁theory ▁predicted ▁that ▁the ▁Sun ▁and ▁the ▁stars ▁would ▁be ▁prominent ▁X - ray ▁sources , ▁there ▁was ▁no ▁way ▁to ▁verify ▁this ▁because ▁Earth ' s ▁atmosphere ▁blocks ▁most ▁extr ater rest rial ▁X - ray s . ▁It ▁was ▁not ▁until ▁ways ▁of ▁sending ▁instrument ▁packages ▁to ▁high ▁alt itude ▁were ▁developed ▁that ▁these ▁X - ray ▁sources ▁could ▁be ▁studied . ▁ ▁The ▁existence ▁of ▁solar ▁X - ray s ▁was ▁confirmed ▁early ▁in ▁the ▁ro cket ▁age ▁by ▁V - 2 s ▁converted ▁to ▁sound ing ▁ro cket ▁purpose , ▁and ▁the ▁detection ▁of ▁extr ater rest rial ▁X - ray s ▁has ▁been ▁the ▁primary ▁or ▁secondary ▁mission ▁of ▁multiple ▁sat ell ites ▁since ▁ 1 9 5 8 . ▁The ▁first ▁cos mic ▁( be yond ▁the ▁solar ▁system ) ▁X - ray ▁source ▁was ▁discovered ▁by ▁a ▁sound ing ▁ro cket ▁in ▁ 1 9 6 2 . ▁Cal led ▁Sc or pi us ▁X - 1 ▁( S co ▁X - 1 ) ▁( the ▁first ▁X -