▁we aker ▁gravity ) ▁will ▁cause ▁the ▁plan ets ' ▁or bits ▁to ▁move ▁farther ▁out . ▁If ▁it ▁were ▁only ▁for ▁this , ▁Ven us ▁and ▁Earth ▁would ▁probably ▁escape ▁inc iner ation , ▁but ▁a ▁ 2 0 0 8 ▁study ▁suggests ▁that ▁Earth ▁will ▁likely ▁be ▁sw allowed ▁up ▁as ▁a ▁result ▁of ▁tid al ▁interactions ▁with ▁the ▁Sun ' s ▁weak ly ▁bound ▁outer ▁en velope . ▁ ▁Grad ually , ▁the ▁hydro gen ▁burning ▁in ▁the ▁shell ▁around ▁the ▁solar ▁core ▁will ▁increase ▁the ▁mass ▁of ▁the ▁core ▁until ▁it ▁reaches ▁about ▁ 4 5 % ▁of ▁the ▁present ▁solar ▁mass . ▁At ▁this ▁point ▁the ▁density ▁and ▁temperature ▁will ▁become ▁so ▁high ▁that ▁the ▁fusion ▁of ▁hel ium ▁into ▁carbon ▁will ▁begin , ▁leading ▁to ▁a ▁hel ium ▁flash ; ▁the ▁Sun ▁will ▁shr ink ▁from ▁around ▁ 2 5 0 ▁to ▁ 1 1   times ▁its ▁present ▁( main - sequence ) ▁radius . ▁Con sequently , ▁its ▁lum inos ity ▁will ▁decrease ▁from ▁around ▁ 3 , 0 0 0 ▁to ▁ 5 4 ▁times ▁its ▁current ▁level , ▁and ▁its ▁surface ▁temperature ▁will ▁increase ▁to ▁about ▁ 4 7 7 0   K . ▁The ▁Sun ▁will ▁become ▁a ▁horizontal ▁giant , ▁burning ▁hel ium ▁in ▁its ▁core ▁in ▁a ▁stable ▁fashion ▁much ▁like ▁it ▁burn s ▁hydro gen ▁today . ▁The ▁hel ium - f using ▁stage ▁will ▁last ▁only ▁ 1 0 0   mill ion ▁years . ▁Event ually ,