▁growth ▁or ▁rep lication . ▁When ▁the ▁liquid ▁drop ▁became ▁too ▁big , ▁it ▁split ▁into ▁two ▁dro ps . ▁Many ▁complex ▁mole cules ▁formed ▁in ▁these ▁" l ittle ▁city ▁econom ies " ▁and ▁the ▁probability ▁that ▁gen es ▁would ▁eventually ▁develop ▁in ▁them ▁was ▁much ▁greater ▁than ▁in ▁the ▁pre bi otic ▁environment . ▁ ▁D ys on ▁sphere ▁▁ ▁In ▁ 1 9 6 0 ▁D ys on ▁wrote ▁a ▁short ▁paper ▁for ▁the ▁journal ▁Science ▁titled ▁" Search ▁for ▁Art ific ial ▁St ell ar ▁S ources ▁of ▁Inf ra red ▁Rad iation ". ▁In ▁it ▁he ▁spec ulated ▁that ▁a ▁techn olog ically ▁advanced ▁extr ater rest rial ▁civil ization ▁might ▁surr ound ▁its ▁native ▁star ▁with ▁artificial ▁structures ▁to ▁maxim ize ▁the ▁capture ▁of ▁the ▁star ' s ▁energy . ▁Event ually ▁the ▁civil ization ▁would ▁enc lose ▁the ▁star , ▁intercept ing ▁elect romagnet ic ▁radiation ▁with ▁w avel ength s ▁from ▁visible ▁light ▁down ward ▁and ▁radi ating ▁waste ▁heat ▁out ward ▁as ▁inf ra red ▁radiation . ▁One ▁method ▁of ▁searching ▁for ▁extr ater rest rial ▁civil izations ▁would ▁be ▁to ▁look ▁for ▁large ▁objects ▁radi ating ▁in ▁the ▁inf ra red ▁range ▁of ▁the ▁elect romagnet ic ▁spectrum . ▁ ▁D ys on ▁conce ived ▁that ▁such ▁structures ▁would ▁be ▁clouds ▁of ▁astero id - s ized ▁space ▁habit ats , ▁though ▁science ▁fiction ▁writers ▁have ▁preferred ▁a ▁solid ▁structure : ▁either ▁way , ▁such ▁an ▁artifact ▁is ▁often ▁called ▁a ▁D ys