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Study: We could detect aliens by their pollution

July 23, 2014
Courtesy of the Harvard-Smithsonian 
Center for Astrophysics
and World Science staff

We might be able to de­tect al­ien life on dis­tant plan­ets through the pol­lu­tion, if any, a new study pro­poses.

Hu­man­ity is on the verge of be­ing able to de­tect signs of al­ien life on oth­er worlds. By stu­dying at­mo­spheres of dis­tant plan­ets, we can look for gas­es like ox­y­gen and meth­ane that only co­ex­ist if re­plen­ished by life. 

But those gas­es come from sim­ple life forms. What about ad­vanced civ­il­iz­a­tions? Would they leave any de­tecta­ble signs?

They might, the re­search pro­poses, if they spew in­dus­t­ri­al pol­lu­tion in­to the at­mos­phere. The stu­dy, by the­o­rists at the Har­vard-Smith­son­ian Cen­ter for As­t­ro­phys­ics, sug­gests we could spot the fin­ger­prints of cer­tain pol­lu­tants, as­sum­ing the at­mos­phere is clear of oth­er, ex­tra­ne­ous ma­te­ri­al. And we might even, sad­ly, find dead civ­il­iz­a­tions that pol­lut­ed them­selves to death—by de­tecting the left­o­ver pol­lu­tion.

The re­search­ers say NASA’s up­com­ing James Webb Space Tel­e­scope should be able to de­tect two kinds of chem­i­cals called chlo­roflu­o­ro­car­bons, or CFCs—ozone-destroying chem­i­cals used in sol­vents and aerosols. The sci­en­tists cal­cu­late that the tel­e­scope could de­tect these if their at­mos­pher­ic lev­els were 10 times those on Earth. A par­tic­u­larly ad­vanced civ­il­iz­a­tion might even in­ten­tion­ally pol­lute the at­mos­phere to make their plan­et warmer—the op­po­site of the glob­al warm­ing that oc­curs on Earth.

But the new de­tection meth­od can only de­tect pol­lu­tants on an Earth-like plan­et cir­cling a white dwarf star, which is what re­mains when a star like our Sun dies. That sce­nar­i­o would max­im­ize the at­mos­pher­ic sig­nal. Find­ing pol­lu­tion on an Earth-like plan­et or­bit­ing a Sun-like star would re­quire a more ad­vanced in­stru­ment. The white-dwarf sce­nar­i­o has re­cently been found to be more prom­is­ing for life than pre­vi­ously thought, though.

While search­ing for those chem­i­cals could fer­ret out an ex­ist­ing al­ien civ­il­iz­a­tion, it al­so could de­tect the rem­nants of a civ­il­iz­a­tion that an­ni­hi­lat­e it­self. Some pol­lu­tants last for 50,000 years in Earth’s at­mos­phere while oth­ers last only 10 years. De­tect­ing mo­le­cules from the long-lived cat­e­go­ry but none in the short-lived cat­e­go­ry would show that the sources are gone.

“In that case, we could spec­u­late that the al­iens wised up and cleaned up their act. Or in a darker sce­nar­i­o, it would serve as a warn­ing sign of the dan­gers of not be­ing good stew­ards of our own plan­et,” said study co-author Avi Loeb of the Har­vard-Smith­son­ian Cen­ter for As­t­ro­phys­ics in Bos­ton. The work has been ac­cept­ed for pub­lica­t­ion in The As­t­ro­phys­i­cal Jour­nal and is availa­ble on­line.


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We might be able to detect alien life on distant planets through its pollution, if any, a new study proposes. Humanity is on the verge of being able to detect signs of alien life on other worlds. By studying atmospheres of distant planets, we can look for gases like oxygen and methane that only coexist if replenished by life. But those gases come from simple life forms. What about advanced civilizations? Would they leave any detectable signs? They might, the research proposes, if they spew industrial pollution into the atmosphere. The study, by theorists at the Harvard-Smithsonian Center for Astrophysics, suggests we could spot the fingerprints of certain pollutants, assuming the atmosphere is clear of other, extraneous material. And we might even, sadly, find dead civilizations that polluted themselves to death—by detecting the leftover pollution. The researchers say NASA’s upcoming James Webb Space Telescope should be able to detect two kinds of chemicals called chlorofluorocarbons, or CFCs—ozone-destroying chemicals used in solvents and aerosols. The scientists calculate that the telescope could detect these if their atmospheric levels were 10 times those on Earth. A particularly advanced civilization might even intentionally pollute the atmosphere to make their planet warmer—the opposite of the global warming that occurs on Earth. But the new detection method can only detect pollutants on an Earth-like planet circling a white dwarf star, which is what remains when a star like our Sun dies. That scenario would maximize the atmospheric signal. Finding pollution on an Earth-like planet orbiting a Sun-like star would require a more advanced instrument. The white-dwarf scenario has recently been found to be more promising for life than previously thought, though. While searching for those chemicals could ferret out an existing alien civilization, it also could detect the remnants of a civilization that annihilated itself. Some pollutants last for 50,000 years in Earth’s atmosphere while others last only 10 years. Detecting molecules from the long-lived category but none in the short-lived category would show that the sources are gone. “In that case, we could speculate that the aliens wised up and cleaned up their act. Or in a darker scenario, it would serve as a warning sign of the dangers of not being good stewards of our own planet,” said study co-author Avi Loeb of the Harvard-Smithsonian Center for Astrophysics in Boston. The work has been accepted for publication in The Astrophysical Journal and is available online.