We've talked a lot about life in the universe in this season — from where we might look, to what it might conceivably be, to the question of what even we mean by the word "life" anyway. And now, finally, it's time to grapple with the huge problem of what astronomers are actually looking for: the signals, the signs, the smoking gun of life on another planet. We're talking biosignatures, and Emily has some bad news: turns out, it's really hard to take a precise measurement of a conclusive biosignature of exolife ... mainly because, it's not clear any such conclusive biosignature even exists. But she has some good news, which is that we're getting a lot better at detecting atmospheres on exoplanets — so there's still hope!

Finally — finally! — Chris and Emily get to the meat of the matter in this season on life in the universe. Very special guest Dr Kelly Redeker from the Department of Biology at the University of York breaks down the principles of life, both on Earth and on other worlds (or "slimy rocks" as Emily insists on calling them). Do you need a Frankenstein-esque spark? Is life inevitable? What about complex life? Intelligent life? And Emily asks Kelly the big question: will we find life outside our planet?

In this season of exploring life in the universe, it's time to consider life closer to home: what are the chances we will find evidence of life — present or past-tense — in our own back yard of the Solar System. Emily's fabuous colleague Dr Clément Moissard, plasma physicist at the University of York, joins us to discuss the chances of finding signs of life on Mars, on the icy moons of Jupiter and Saturn ... and even on Pluto?! Surely not. It's a fascinating and fun conversation with plenty of surprises: Chris somehow missed the fact that we landed on Titan in 2005, Clément is super keen to visit mysterious Planet 9, and Emily just seems fixated on tasty space fish.

Having established that the hunt for life in the galaxy ought to begin with an appropriate star, Emily turns our attention towards suitable planets. But what makes a hospitable home for life? It’s complicated, and it seems whatever way we look at it, we don’t have a lot of candidates to choose from. Emily discusses earth-like rocky planets, ocean worlds, and wonderfully-named Chthonian planets, before letting rip with some wild speculation. I mean, life could be anywhere, right?

We're back with Season 3. For the next six epiosodes we're talking life in the universe, and so far we have N=1: we know there's life on Earth, but nowhere else as yet. Those are challenging statistics. In this episode Emily makes the case that to explore the possibility of life elsewhere in the cosmos, you need planets — and to have planets, you need stars. She then proceeds to whittle the number of potential life-bearing systems in our galaxy down to a scarily small number. But all is not lost, we still have five episodes to fill with hope and optimism.

According to one survey, around one-third of Australians think aliens not only exist, but have actually visited Earth. That's ... a bit fraction. In this final episode of season 2, we ask how we'd even find out if life exists around other stars. Emily introduces the Habitable Worlds Observatory, an incredible new space telescope that's just in the early design phase and not due for years yet, with lots of technical and scientific holes to plug. Whether we can find life on other planets, who knows ... but maybe we've just found season three of Syzygy!