"The sad truth of the matter is that earth-like planets are near cosmic specks of dust. And therefore detecting them is really quite hard."

 

Hard, but not impossible. Every now and again, the planet passes directly between us and the star. And if it does that, it's like a little eclipse. And the star-light drops. It gets darker because the planet is blocking the light from that star. And it turns out we can see that.

 

With this in mind, scientists built one of the world’s most sensitive telescopes and launched it into space. The mission called Kepler may not help us find E.T, but it could help us find its home.

 

"Kepler will simply do one thing unbelievably well--measure the brightness of 100,000 stars over and over and over, looking for a few of those 100,000 stars that dim."

 

Seeing the tiniest dim from a small planet travelling in front of a star thousands of light-years away isn’t easy to imagine. But the Kepler telescope is one of the most sensitive cameras ever built.

 

"To give you an idea of just how sensitive Kepler is, I’m gonna demonstrate using this massive World War II search light. The brightness of that search light represents the extreme luminosity of stars. And I’m gonna use this tiny marble to represent the planet. When this planet passes in front of the star, it blocks out a tiny fraction of the light, dimming the star by a very small amount, and that’s exactly what the Kepler space craft can detect."

 

Kepler can detect a 0.01% change in the star’s luminosity, but even if it spots a dimming star, there’s still another problem. 

 

"When Kepler sees a star that dims, it could be due to a speck of dust that crossed in front of the telescope. There’s a possibility of binary stars, two stars that orbit each other thereby dimming the stars as one blocks the other."