screengrab There are two types of aliens that humans could detect within the next century:

Primitive, microbial life forms within our solar system. An intelligent, advanced alien race that could turn our entire way of life upside down.

NASA, along with other space agencies around the world, are making impressive strides toward uncovering the first one — life within our solar system. But until now, the prospects of finding intelligent ET have been low.

Two astrophysicists have recently developed a radical new approach in the search for intelligent alien life, and they say it could help us discover signals from an advanced alien race – if any exist — within the next 70 years.

Thinking outside the box

NASA Goddard Spaceflight Center Instead of looking at how humans might detect extraterrestrials, the researchers studied how extraterrestrials might discover us.

It's possible that aliens might already know Earth exists, contains life, and they're attempting to contact us right now.

The big question, then, is how would they find us?

Admittedly, it's impossible to know what potential alien scientists are thinking, but when it comes to the search for distant planets, the options are limited by the geometry of space. Therefore, it's not ridiculous to imagine that aliens might discover Earth using the same techniques that astronomers use here on Earth.

With that in mind, Max Planck Institute for Solar System Research astrophysicist René Heller and McMaster University astrophysicist Ralph Pudritz mapped out a narrow band in the night sky of the most likely places we could receive signals from intelligent aliens.

Measuring the brightness of stars

The main method astronomers use to look for exoplanets is to measure the brightness of distant stars.

Exoplanets alone are small and dim, but they make themselves known by passing in front of a star.

When that happens, the planet blocks out some of the light and the overall brightness decreases, which astronomers then measure to determine the planet's size, as shown in the animation below:

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While this is an effective planet-hunting approach, it can only detect a plant as long as the star and exoplanet are along Earth's line of sight.

As a result, while there may be thousands of exoplanets out there, we may never observe or study many of them.

And although that's somewhat depressing, Heller and Pudritz realized that this same limitation applies to any extraterrestrials out there who might be using the same technique.

Narrowing the search

Axel Quetz (MPIA) / Axel Mellinger, Central Michigan University Going from that notion, they reversed the scenario that we use to hunt for aliens and instead plotted where in the sky distant observers could witness Earth passing in front of our Sun.

It turns out that it's a relatively small area (labeled in the diagram above as "Earth's Transit Zone), about two thousandths the size of the entire sky. That already narrows the search quite a bit, but Heller and Pudrtiz went one step farther.

They looked at all of the stars within that area similar to our Sun — since some think the best chances for the evolution of intelligent life is around Sun-like stars. They found 82 stars, which can now serve as a useful catalogue for SETI initiatives.

"The key point of this strategy is that it confines the search area to a very small part of the sky," Heller said in a press release. "As a consequence, it might take us less than a human life span [about 70 years] to find out whether or not there are extraterrestrial astronomers who have found the Earth."