As the universe's only known harbor for life, Earth is arguably one strange rock. But light-years from our solar system, other intelligent beings on a similar planetary oasis might be gazing in our direction and seeing us as a sign that they're not alone in the universe.
To date, astronomers have confirmed the existence of nearly 4,000 planets beyond our solar system, including some that just might have the conditions necessary to support life as we know it. As our technology improves, we should be able to learn more about these worlds and their chances of hosting plants, animals, and maybe even civilisations.
That means if aliens are out there, they could just as easily discover us.
First, they'd need to find Earth from afar, either by watching our sun wobble as the planet's gravity tugs against it, or by seeing the sun dim as Earth blocks a tiny fraction of sunlight during its orbit. Nine known alien worlds can see Earth transit across our sun, just as we've seen thousands of alien planets dim their host stars.
Once spotted, our planet would likely intrigue E.T. Our sun is relatively stable, not prone to disastrous flares that'd rip our atmosphere to shreds. What's more, we fall squarely within our sun's habitable zone, the area around a star where liquid water can persist on a planet's surface.
Faraway scientists might then attempt to spot our atmosphere, to see whether life's thumb is on the chemical scales. But what would they be looking for? And could they really infer life's presence across trillions of miles?
To read more, click here.