Don’t Ex­pect E.T. to Call Home

The Economic Times - - Breaking Ideas - Shob­hit Ma­ha­jan

On Fe­bru­ary 22, 2017, the Na­tional Aero­nau­tics and Space Ad­min­is­tra­tion (Nasa) an­nounced the dis­cov­ery of seven Earth-sized planets or­bit­ing a star. The dis­cov­ery of these planets is of ex­treme im­por­tance and will go a long way in solv­ing some of the mys­ter­ies of planet for­ma­tion.

Of course, the fact that all of these are at a dis­tance from their par­ent star, where liq­uid wa­ter can ex­ist, is what makes it even more im­por­tant. Liq­uid wa­ter is thought to be the most im­por­tant in­gre­di­ent for life, as we know it, to ex­ist in the uni­verse.

The planets were dis­cov­ered in the con­stel­la­tion of Aquar­ius and are or­bit­ing a rel­a­tively cool, dim star of the type known as M dwarfs. These are pos­si­bly the most com­mon stars among the bil­lions in our galaxy, the Milky Way, on the edge of which our so­lar sys­tem lies. The star, Trap­pist-1, is close by astro­nom­i­cal stan­dards: about 40 light years (235 tril­lion miles) away from Earth. These ex­o­plan­ets — so called since they are lo­cated out­side our own so­lar sys­tem — add to the list of thou­sands that have been dis­cov­ered since their first sight­ing in 1988.

Search­ing for ex­o­plan­ets is chal­leng­ing. Their size is typ­i­cally too small for a di­rect sight­ing even with the big­gest tele­scopes. How­ever, astro- nomers use in­ge­nious meth­ods to in­fer their pres­ence and to quan­tify their prop­er­ties. Typ­i­cally, when the ex­o­planet passes be­tween its par­ent star and Earth, there is a dim­ming of the starlight and this can be used to de­tect the ex­o­planet. The fact that the changes in the starlight are ex­tremely mi­nus­cule means that al­most all the ex­o­plan­ets dis­cov­ered are in the Milky Way.

Us­ing the Tran­sit­ing Planets and Plan­etes­i­mals Small Te­le­scope (Trap­pist) te­le­scope in Chile, astronomers de­tected the pres­ence of this ex­o­planet sys­tem that has been given the unimag­i­na­tive moniker Trap­pist-1. Then, us­ing the Spitzer Space Te­le­scope (SST) for more de­tailed ob­ser­va­tions, they were able to de­ter­mine the den­si­ties and sizes of the ex­o­plan­ets. All of them turned out to be rocky blobs, hav­ing a mass very close to our own blue planet’s.

All the ex­o­plan­ets are lo­cated fairly close to the star. All of them are closer to their star than Mer­cury is to the Sun. One would as­sume that the planets would be boil­ing hot at such a dis­tance. How­ever, the fact that the par­ent star is rel­a­tively cool, with a sur­face tem­per­a­ture of around 2,500° C — com­pared to the Sun with 5,600° C — makes these planets rel­a­tively balmy.

And this means that wa­ter, the elixir of life, could ex­ist in its liq­uid form at least at some lo­ca­tions on them. The re­gion around a star where wa­ter can ex­ist in its liq­uid form is called the hab­it­able zone. And this is the largest hab­it­able zone found as yet with seven planets.

Their or­bital pe­ri­ods are also mod­est with the clos­est one or­bit­ing the star once in 2.4 days and the far­thest in 12 days. How­ever, like our own Moon, which al­ways has only one face to­wards Earth, they seem to be locked into the grav­i­ta­tional pull of their par­ent star. As a re­sult, only one side faces the star. One side is al­ways day and the other night. This means that there would be ex­treme changes in tem­per­a­ture and, hence, weird weather pat­terns.

Fas­ci­na­tion with dis­cov­er­ing ex­trater­res­trial life is an old one. It is now gen­er­ally agreed that given the im­men­sity of the cos­mos and the or­di­nar­i­ness of our own planet, life al­most cer­tainly ex­ists in some form at many places in the uni­verse. Of course, find­ing it is an­other ball game al­to­gether.

The Search for Ex­tra-Ter­res­trial In­tel­li­gence (Seti), the largest and the long­est ded­i­cated project to look for ex­trater­res­trial life, has so far re­turned a naught. Fur­ther­more, not­with­stand­ing the PR hype sur­round­ing this Nasa an­nounce­ment, it is un­likely that these ex­o­plan­ets are hab­it­able. Yes, the pos­si­bil­ity of find­ing liq­uid wa­ter on them is high. But the par­ent star emits as much X-rays and ul­tra­vi­o­let ra­di­a­tion as our Sun does, and given that the planets are so close to their par­ent, the ra­di­a­tion would make life as we know it ex­tremely im­prob­a­ble.

Nev­er­the­less, be­cause the plan­e­tary sys­tem is rel­a­tively close, there’s a lot that these planets could help us learn. Planet for­ma­tion is one such area.

And any thought of send­ing mis­sions to these planets or, in­deed, even hu­mans to ex­plore them can only be hubris.

At a dis­tance of 40 light years, any sig­nal sent to­day to or from the space­craft would only reach af­ter a gen­er­a­tion-and-a-half. Don’t ex­pect E.T. to call home any­time soon.

The writer is pro­fes­sor, physics and as­tro­physics, Univer­sity of Delhi

Cap­tain, logic dic­tates that we’ll first have to build a real space­ship

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