We think we know what it means when we see certain road signs? NASA Goddard Space Flight Center, CC BY David Kipping What would it take to hide an entire planet? Seems more like a question posed in an episode of? Star Trek? than in academic discourse, but sometimes the vanguard of science is confused with themes found in science fiction.
Of course, weve been leaking our own position to distant stars through radio and television signals for decades, largely ignorant of the cosmic implications.
But several notable scientists, such as Stephen Hawking, have publicly expressed their concern to reveal our presence to other civilizations.
These concerns derive largely from the darkest chapters of our own history, when a more advanced civilization would subdue and replace a less advanced civilization.
It may be too late to retire to invisibility, but perhaps not to other intelligent alien civilizations out there.
The inhabitants of a distant planet may prefer to hide from people like us.
In 2016, my undergraduate student Alex Teachey and I published an article that proposes a way to cover up planets, as well as a way to convey the existence of a civilization.
Even if were not manipulating our own signal in this way, it doesnt mean that other planets arent.
Is it possible that what we see as we examine the universe in search of other habitable planets?? was designed to disguise or highlight the existence of other civilizations.
Tracking transits to find other planets before we talk about how to hide a planet from distant voyeurs, consider the best way weve figured out to find one.
Humanitys most successful technique for detecting other planets is the transit method.
A traffic occurs when a planet seems to pass in front of its parent sun, blocking part of the starlight for a few hours.
So if we have our telescopes pointed at a part of the universe and a star seems to disappear for part of the day, it tells us that a planet has temporarily stood between us as it continues in its orbit.
Using this technique, NASAs Kepler mission discovered several thousand planets.
It seems likely that any advanced civilization would be aware of this simple method.
Each time a planet transits its star, its existence is essentially being announced to all points situated along the same plane of the planet and the star.
An advanced civilization may not mind having the location, size, and even atmospheric chemistry of its planet advertised throughout the cosmos.
Or you may wish to hide your presence.
If this is the last case, she may choose to build a cloak of invisibility.
It turns out that hiding planetary planets from the transit method would be surprisingly easy, so easy that we Earthlings could do it now, if we wanted to.
Since transits appear as a decrease in the brightness of a distant star, our hypothetical mantle simply produces the opposite brightness increase.
Lasers provide an efficient means to contain this drop in brightness.
All the power of a laser is contained in a relatively narrow beam, as opposed to spreading in all directions as starlight does.
Because of the way light spreads as it travels ? called diffraction ? the laser beam would spread to encompass entire solar systems after traveling many light years through space, bathing that distant planetary system inside the concealment beam.
No drop in glow makes it look like theres no planet there.
A laser cover capable of hiding the Earth from an alien version of NASAs Kepler mission would require 30 megawatts of energy at maximum intensity, approximately the equivalent of 10 wind turbines of power..