A new book: An Introduction to Planetary Defense: A Study of Modern Warfare Applied to Extra-Terrestrial Invasion - examines preparedness of the planet for alien invasion of a warring kind. WHEN the aliens finally invade Earth, you may wish you had listened to Travis Taylor and Bob Boan. And if the invasion follows the plot of a typical Hollywood blockbuster, they might also be the guys called in at the last minute to save the day. After all, they have written An Introduction to Planetary Defence, a primer on how humanity can defend itself if little green men wielding death rays show up at our cosmic doorstep. And, yes, they’re serious.  Via: Daily Telegraph

“The probability is there that aliens exist and are old enough to have technology to enable them to come here,” Taylor said.

Taylor and Boan are hardly basement-dwelling paranoids obsessed with tinfoil hats and Area 51.

Taylor holds advanced degrees in astronomy and physics. He and Boan have done consulting work for the Defence Department and the US space agency NASA.

Taylor acknowledges alien invasion is hardly a mainstream concern but says it is naive to assume that any beings advanced enough to master star travel will have evolved beyond war.

“It’s a wonderful idea that has no basis in reality,” Taylor said.

Taylor and Boan plugged in what they felt were conservative estimates, such as that aliens cannot travel faster than 10 per cent of the speed of light.

After crunching the numbers, they say it is possible that our Milky Way galaxy harbours thousands of intelligent alien species and that there is a “high probability” that one or two of them visit Earth every century.

But if there are so many aliens out there, why haven’t we heard from them already?

That is the question famously posed by the physicist Enrico Fermi in 1950 to dismiss speculation by his colleagues that intelligent life should be routine.

Taylor and Boan are convinced Fermi got it wrong. Even if aliens used god-like technology to jump across thousands of light years in a single day, they would still need millions of years to explore all the star systems in the galaxy.

They simply may not have stumbled across our neck of the woods yet.

Taylor and Boan started thinking about how to respond to an aggressive extraterrestrial attack during a 2001 discussion about defending against terrorist attacks.

Failure to prepare may mean mankind will have to dig in and fight with improvised weapons and hit-and-run tactics, much the same way Islamic extremists have battled the US military in Iraq, Taylor says.

“You’d have to create an insurgency, a mujahideen-type resistance,” Taylor said.