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Humans have long gazed up at the night sky, wondering whether other lifeforms and intelligences could be thriving on worlds far beyond our own.

Answering that question seemed fated to remain pure speculation. But over the last few decades, ultra-sensitive telescopes and dogged detective work have transformed alien planet-hunting from science fiction into hard fact. Gone are the days of speculation; the hunt for extraterrestrials has become a matter of serious scientific inquiry.

As the hunt for alien worlds began, we expected to find worlds similar to the planets in our own solar system, but we instead discovered a riot of exotic worlds. Vivid animation based on data from the most successful planet hunter of them all, the Kepler space telescope, brings these worlds into view: puffy planets with the density of polystyrene, unstable worlds orbiting two suns and 1,000-degree, broiling gas giants with skies whipped into titanic winds.

But perhaps the most startling discovery was the number of worlds that may be contenders for a second Earth. Our latest survey of the galaxy estimates that there are billions of rocky planets at the right distance from their sun to have that ingredient so crucial for life as we know it, liquid water. Amongst them, we witness the most tantalizing discovery of all: a so-called ‘super-Earth’, situated in the Goldilocks zone - the area just the right distance from a sun to potentially support life - and with the faint signal of water in its atmosphere.

With over 2,800 exoplanets confirmed by Kepler and discoveries still rolling in, Brian lays out his own answer to the age-old question with thrilling new science: are we alone?