Anti-alien cloak­ing de­vice

Astronomers have de­vised a laser-based ‘cloak­ing de­vice’ to hide our planet from po­ten­tial alien ag­gres­sors, says Fred Wat­son.

Australian Geographic - - Contents -

ONCE IN A WHILE, some­one sug­gests an idea that’s so far out of the box it takes your breath away. It hap­pened most re­cently at the end of March – so near the end of March, in fact, that it seemed sus­pi­ciously close to 1 April. It’s the work of two astronomers at New York’s Columbia Univer­sity, and it’s a very thought-pro­vok­ing idea.

You’re prob­a­bly aware that one of the most ef­fec­tive ways of dis­cov­er­ing a planet or­bit­ing a dis­tant star is to ac­cu­rately mon­i­tor the star’s bright­ness. If there’s a planet that crosses in front of the star it’s or­bit­ing, as seen from Earth, its pas­sage across the star’s face will briefly dim the bright­ness of the star.

Ad­mit­tedly – it’s only by a very small amount. If you were an alien watch­ing our So­lar Sys­tem, Jupiter would cause a 1 per cent drop in sun­light as it crossed the Sun’s disc, while our own planet would dim it by a mere 0.01 per cent. But that dif­fer­ence is enough to be de­tected from space; this is why NASA’s Ke­pler space­craft has been so suc­cess­ful at dis­cov­er­ing Earth-sized plan­ets around other stars, sim­ply by star­ing at a large se­lec­tion of can­di­dates.

Now imag­ine we’ve dis­cov­ered that there’s other in­tel­li­gent life in the uni­verse, and we’re gripped with in­ter­stel­lar xeno­pho­bia. How can we hide our planet? Re­mem­ber­ing that aliens are likely to find us only if the Earth crosses the Sun’s disc from their view­point, we can mask the re­sul­tant dim­ming by fir­ing a laser to­wards them as that is hap­pen­ing. It means point­ing the laser in the di­rec­tion op­po­site to the Sun through­out the year, a rel­a­tively straight­for­ward pro­ce­dure.

Be­fore you start to breathe more eas­ily about the threat of alien in­va­sion, how­ever, there are sev­eral prob­lems. Lasers only emit light of one colour, so you’d need many of them to cover the whole rain­bow spec­trum of sun­light. And the au­thors ad­mit that the tech­nique might ac­tu­ally turn out to be bet­ter at ad­ver­tis­ing our pres­ence than hid­ing it. Oops.

FRED WAT­SON is an as­tronomer at the Aus­tralian Astro­nom­i­cal Ob­ser­va­tory.

A laser helps the Euro­pean South­ern Ob­ser­va­tory’s Very Large Tele­scope cap­ture sharp im­ages.

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