Earth-like worlds are yet to be born, study says

WASHINGTON: Earth came early to the par­ty in the evolv­ing uni­verse, ac­cord­ing to a new the­o­ret­i­cal stu­dy. It con­cludes that only eight per­cent of po­ten­tially hab­it­a­ble plan­ets have even formed yet.
But many fu­ture civ­il­iz­a­tions may arise so late that by then, ev­i­dence for the Big Bang—the explosion-like event that gave birth to the uni­verse—will have dis­ap­peared.

The con­clu­sion is based on an as­sess­ment of da­ta col­lect­ed by NASA’s Hub­ble Space Tel­e­scope and the pro­lif­ic plan­et-hunting Kep­ler space ob­serv­a­to­ry.
“Com­pared to all the plan­ets that will ev­er form in the uni­verse, the Earth is ac­tu­ally quite ear­ly,” said study au­thor Pe­ter Beh­roozi of the Space Tel­e­scope Sci­ence In­sti­tute in Bal­ti­more, Md.
Look­ing far away and far back in time, Hub­ble has giv­en as­tro­no­mers a “family al­bum” of gal­axy ob­serva­t­ions that chron­i­cle the uni­verse’s star forma­t­ion his­to­ry as ga­lax­ies grew.
The da­ta show, the re­search­ers said, that the uni­verse was mak­ing stars quickly 10 bil­lion years ago, but the frac­tion of the uni­verse’s hy­dro­gen and he­li­um gas that was in­volved to make those stars was very low. To­day, star birth is hap­pen­ing much more slow­ly, but there is so much left­o­ver gas avail­a­ble that the uni­verse will keep cook­ing up stars and plan­ets for a very long time.

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“There is enough re­main­ing ma­te­ri­al to pro­duce even more plan­ets in the fu­ture, in the Milky Way and be­yond,” said co-invest­iga­tor Molly Peeples of the in­sti­tute.
Kep­ler’s plan­et sur­vey in­di­cates that Earth-sized plan­ets in a star’s hab­it­a­ble zone, the per­fect dis­tance that could al­low wa­ter to pool on the sur­face, exist all over our gal­axy. Sci­en­tists pre­dict there should be a bil­lion Earth-sized worlds in the Milky Way gal­axy now, a good por­tion of them pre­sumed to be rocky, like ours. That es­ti­mate sky­rock­ets when you in­clude the oth­er 100 bil­lion ga­lax­ies in the ob­serva­ble uni­verse.
This leaves plen­ty of op­por­tun­ity, they said, for un­told more Earth-sized plan­ets in the hab­it­a­ble zone to arise in the fu­ture. The last star is­n’t ex­pected to burn out un­til 100 tril­lion years from now. That’s plen­ty of time for an­y­thing to hap­pen on the plan­et land­scape.

The re­search­ers say that fu­ture Earths are more likely to ap­pear in­side gi­ant gal­axy clus­ters and al­so in dwarf ga­lax­ies, which have yet to use up all their gas for build­ing stars and ac­com­pa­nying plan­etary sys­tems. By con­trast, our Milky Way gal­axy has used up much more of the gas avail­a­ble for fu­ture star forma­t­ion.