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