▁of ▁Earth ) ▁li br ates ▁around ▁zero . ▁This ▁means ▁that ▁the ▁center ▁of ▁the ▁" k id ney " ▁moves ▁back ▁and ▁forth ▁over ▁a ▁period ▁of ▁years , ▁from ▁being ▁in ▁front ▁of ▁Earth ▁to ▁being ▁behind ▁Earth , ▁but ▁this ▁movement ▁is ▁centered ▁on ▁Earth . ▁ ▁It ▁became ▁a ▁quasi - s at ellite ▁at ▁least ▁ 7 7 5 ▁years ▁ago ▁and ▁will ▁stop ▁being ▁that ▁ 1 6 5 ▁years ▁from ▁now ▁after ▁a ▁" close " ▁encounter ▁with ▁Earth ▁( 0 . 1 3   AU ). ▁This ▁quasi - s at ellite ▁episode ▁will ▁have ▁had ▁a ▁duration ▁of ▁around ▁a ▁thousand ▁years ▁or ▁more , ▁but ▁less ▁than ▁ 2 , 5 0 0 ▁years . ▁Before ▁and ▁after ▁this ▁episode ▁it ▁passes ▁in ▁and ▁out ▁of ▁other ▁types ▁of ▁co - orb ital ▁or bits , ▁such ▁as ▁being ▁a ▁tro jan ▁or ▁a ▁" pass ing ▁object " ▁( one ▁whose ▁relative ▁longitude ▁to ▁Earth ▁can ▁att ain ▁any ▁value , ▁which ▁is ▁not ▁the ▁case ▁for ▁a ▁quasi - s at ellite ▁or ▁a ▁Tro jan ). ▁ ▁Phys ical ▁properties ▁▁ ▁With ▁an ▁absolute ▁magnitude ▁of ▁ 2 2 . 9 , ▁it ▁has ▁an ▁estimated ▁diameter ▁of ▁approximately ▁ 1 7 0 ▁meters ▁for ▁an ▁al bed o ▁of ▁ 0 . 2 5 , ▁which ▁is ▁typical ▁for ▁st ony ▁astero ids . ▁ ▁See ▁also ▁ ▁References ▁▁▁▁ ▁Further ▁reading ▁ ▁Under standing ▁the ▁Distribution ▁of