Pansper­mia and the Drake Equa­tion: Look­ing good

Lethbridge Herald - - READER’S FORUM -

One by one, the empty boxes in the Drake Equa­tion are be­ing filled in with ac­tual num­bers, and it’s look­ing good. So good that Yuri Mil­ner is spend­ing $100 mil­lion of his own money over the next 10 years to fund the search for non-hu­man civ­i­liza­tions or­bit­ing other stars. But it’s a pity that the Phi­lae lan­der from the Euro­pean Space Agency’s Rosetta mis­sion didn’t have more time to look for life on Comet 67P/Churyu­movGerasi­menko.

Yuri Mil­ner is a Sil­i­con Val­ley bil­lion­aire who was work­ing on a PhD in the­o­ret­i­cal physics at the Rus­sian Academy of Sciences be­fore he moved to the United States and got rich. His money will buy thou­sands of hours of ra­dio-te­le­scope time each year to look for ra­dio trans­mis­sions from other star sys­tems.

This rep­re­sents at least a ten­fold in­crease in the amount of work be­ing done on find­ing in­tel­li­gent life else­where in the gal­axy, and Yuri Mil­ner is no fool. Why does he think it’s worth spend­ing this money now?

Prob­a­bly be­cause the Drake Equa­tion is fi­nally com­ing into its own. It has seven terms, and Amer­i­can as­tronomer Frank Drake could not give a value to any of them when he first wrote it in 1961. It was just a for­mula that would let us es­ti­mate the num­ber of civ­i­liza­tions in the Milky Way gal­axy when the rel­e­vant data even­tu­ally be­came avail­able.

To fill in the first three terms, we needed to know how many stars there are in the gal­axy, how many of them have plan­ets, and how many of those plan­ets are in the “hab­it­able zone” where liq­uid wa­ter can ex­ist.

In 1961 the es­ti­mate was 100 bil­lion stars. Now it is 400 bil­lion, of which 300 bil­lion are es­sen­tially sim­i­lar to our Sun.

Un­til 1992, we didn’t even know if other stars had plan­ets cir­cling them. Now we can es­ti­mate that at least 40 per cent of them do, although the real an­swer may be al­most all of them. ( We still can­not de­tect plan­ets much smaller than Earth).

As for how many plan­ets are in the “hab­it­able” zone, not too close or too far from their par­ent star, the an­swer is prob­a­bly one or two per star.

Us­ing the data ac­quired in the past 20 years, NASA now es­ti­mates that there are 144 bil­lion hab­it­able plan­ets in our gal­axy. Not all of them will har­bour life, of course, but that is a very en­cour­ag­ing num­ber.

Other ques­tions re­main, how­ever. How many “hab­it­able” plan­ets will ac­tu­ally have life on them? On how many of those plan­ets will an in­tel­li­gent species ap­pear? How many of those in­tel­li­gent species will build civ­i­liza­tions that use elec­tro­mag­netic com­mu­ni­ca­tions? And how long, on av­er­age, would those high-tech civ­i­liza­tions last?

We don’t yet know the an­swers to any of those ques­tions, but we do know that or­ganic com­pounds are com­mon even in in­ter­stel­lar space, and that they are con­tin­u­ously rain­ing on our own planet. So the stan­dard as­sump­tion is that they some­how com­bined on Earth to form the first sin­gle-celled crea­tures, and evo­lu­tion did the rest.

But if it were easy for those or­ganic com­pounds to com­bine into com­plex mi­crobes and viruses, then you would ex­pect it to have hap­pened here a num­ber of times. There would be sev­eral or many un­re­lated ge­netic lin­eages on Earth — and there aren’t. All life here has a com­mon an­ces­tor.

So it must be very rare for life to de­velop spon­ta­neously. If it ac­tu­ally hap­pened here, it would mean that we are a mir­a­cle, and pretty much alone in the gal­axy. But maybe the mir­a­cle hap­pened on another of those 144 bil­lion plan­ets, bil­lions of years ago, and life been spread­ing through the gal­axy ever since — not as alien be­ings on star­ships, but as mi­crobes and viruses on me­te­orites and comets.

This is the “pansper­mia” hy­poth­e­sis, first pro­posed by astronomers Sir Fred Hoyle and Dr Chan­dra Wick­ra­mas­inghe in 1974. Dis­sat­is­fied with the no­tion that Earth was unique, they sug­gested that not only or­ganic com­pounds but ac­tual mi­crobes and viruses could travel through in­ter­stel­lar space, dor­mant but still vi­able in the liq­uid wa­ter that they sus­pected was present in the in­te­rior of many comets.

It sounds weird, but it is just as plau­si­ble as the ri­val hy­poth­e­sis of an in­de­pen­dent ori­gin of life on Earth. Comet 67P/Churyu­movGerasi­menko was the first-ever op­por­tu­nity to see if this hy­poth­e­sis holds wa­ter (so to speak). The Phi­lae lan­der did de­tect 16 dif­fer­ent or­ganic mol­e­cules as it bounced along the comet’s sur­face, but it ended up in the shad­ows with­out power to pur­sue its in­ves­ti­ga­tions fur­ther.

Pity, but there’ll be another comet along in a while. And if it turns out that Hoyle and Wick­ra­mas­inghe were right, then most of those 144 bil­lion plan­ets will have life on them. The history of evo­lu­tion on Earth tends al­ways to greater com­plex­ity, so a fair pro­por­tion of them would have in­tel­li­gent life on them.

How many of them have high­tech civ­i­liza­tions on them at the mo­ment, of course, de­pends on how long the av­er­age tech­no­log­i­cal civ­i­liza­tion sur­vives. Our own hitech civ­i­liza­tion has sur­vived, so far, for about one cen­tury.

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