Is Our Galaxy Filled With Alien Space Probes

Ever wonder if aliens have been spying on us? You're not alone. In a provocative new paper, a pair of astrophysicists consider the possibility that intelligent alien beings could have built a fleet of self-replicating space probes that use gravity to sling themselves from star to star.

"We're saying that "if" aliens build self-replicating probes, they could explore the entire Milky Way in about ten million years," study co-author Dr. Duncan Forgan, a postdoctoral fellow at the University of Edinburgh's Institute for Astronomy, told The Huffington Post in an email.

Ten million years is a relatively short timespan, given that scientists estimate the universe is around 13.8 billion years old.

How could such probes make copies of themselves? Dr. Duncan said that we humans seem to be closing in on the necessary technology ourselves, and "with current 3D printing tech, it might only be a century or two before humans figure it out!"

Travel by slingshot effect -- also called gravity assist -- isn't as wacky as it sounds either. When a probe passes near a planet, it can get a boost in speed from the planet's gravity. NASA has exploited the phenomenon on many occasions--perhaps most notably with the Voyager I and II space probes. Launched in 1977, the probes used gravity assist to reach the edge of our solar system.

Alien probes using the same slingshot maneuvers wouldn't have to depend on powerful engines or massive amounts of fuel. And they could explore the galaxy 100 times faster than probes navigated by powered flight, Dr. Duncan said.

The paper, entitled "Slingshot Dynamics for Self-Replicating Probes and the Effect on Exploration Timescales," was published in the "International Journal of Astrobiology".