In September 2017, two kilometres deep beneath the South Pole, a tiny but very speedy neutrino collided with an atom in the ice and created a flash of light. The flash was picked up by a few of the more than 5,000 photodetectors that comprise the IceCube Neutrino Observatory, and immediately the banks of computers at the surface sent out an alarm to astronomers across the globe: we’ve found one!

Astronomers pointed their telescopes back along the neutrino’s path, and searched for a source. Eventually they found one: an exotic entity known as a blazar, a supermassive black hole at the core of a galaxy 3.7 billion light years away, spewing out an intense beam of high-energy particles that happens to be pointing right at us.

A single neutrino, heralding an exciting new era of multi-messenger astronomy.

A question from a listener leads us into some very tall weeds as we ponder the nature of light: what is it, exactly? It is a wave? Or a particle? Or, somehow, both at once? And photons, the massless particles that apparently make up all light: if they've got no mass, how can they be affected by gravity — like around a black hole, for example? Oh, it's all very tricky stuff, but we have lots of fun unpacking it all. Because in the end, you can't do much astronomy without light, so it's best to understand it properly, really.

Black holes: a staple of quality science fiction for decades now ... but what actually *are* they? Awesome, is one answer. Astronomers reported a few weeks ago fresh evidence for a black hole tearing a star apart in a distant galaxy — gruesome, sure, but fascinating too. In this eipisode we chat about black holes and come to the conclusion that they warp our brains like the fabric of space-time itself.

It's episode 10! We celebrate with cake and a chat about how how astronomers become astronomers. Emily describes her (slightly unusual and a bit cheeky) path to her current career as Astronomer Extraordinaire and Director of the University of York's Astrocampus. Then we explore all the different skills and job titles that fall under the broad umbrella of "working in Astronomy". And of course, even if you don't want to do it as a job, there's a very long and distinguished history of amateur astronomy to discover. Really, there's no reason *not* to get involved.

A few weeks ago NASA gathered journalists from across the globe for an announcement about something they'd found on Mars. Naturally, the collective imagination went *nuts*, because surely, SURELY this was going to be The Big Announcement: finally, the discovery of Life Elsewhere In The Universe! Turns out, nope ... but NASA did have some very cool things to talk about. Curiosity, the Mars Rover that just keeps on keeping on, has found seasonal changes in methane levels, which *could* be produced by biological mechanisms. It also found a bunch of interesting organic molecules in the martian soil. Neither of these discoveries say that life ever existed on Mars, but they're both tantalising whispers urging us to keep looking, keep looking ...

At the XXVIth General Assembly of the International Astronomical Union, held in Praague in August 2006, a new set of three criteria were decided to define what is — and what is emphatically *not* — a planet. Infamously, Pluto fulfilled only two of the three criteria, and so was unceremoniously dumped from the planet club, and reclassified as a "dwarf planet". A decade later, the New Horizons spacecraft swung past this tiny, frozen rock on the outskirts of the Solar System and reported back that Pluto is actually a pretty fascinating place, with a loads of cool suface features and even a thin atmosphere capable of creating dunes of solid methane! Dwarf planet it may be, but Pluto is still awesome.

So, apparently, octopuses come from space. Or something. Emily and Chris chat about a ... curious ... paper that came out recently, which proposes an explanation for the Cambrian Explosion, the huge increase in diversity of life across the planet 500 million years ago. The suggested cause? Possibly viruses from space ... possibly octopus eggs in a meteor ... oh, who knows? It all seems a tad speculative but it's fun to discuss anyway.

Some astronomers found signs of great plumes of water erupting from the surface of Europa, one of the larger moons of Jupiter — and water could mean life, which has everyone jumping around in excitement. The best bit? They found the evidence buried deep in archived data from a 20-year-old space mission. See, *that's* why you don't just throw away old files — you never know what you'll find!

Astronomers have spotted a cluster of 14 galaxies far, far away, so piled up on top of each other, and so soon after the Big Bang, that they’re forcing the theorists to check back over their models and simulations of how the universe evolved. It’s an episode chock-full of big things, from galaxies, to clusters of galaxies, to superclusters, to filaments of superclusters … It’s all a bit overwhelming really.

Back in 2008 a large chunk of rock hurtled into the Earth’s atmosphere. Most of it burned up on the way down, but some fragments of the meteorite landed in the deserts of Sudan. When scientists open up those fragments and examined them under a microscope, they found something very interesting: tiny, tiny, diamonds. Nanodiamonds!

Ten years later, in April 2018, planetary scientists published a paper in Nature arguing that the structure of those nanodiamond crystals could only have come from one place: deep inside a planet — a planet that no longer exists in our Solar System.

Tiny diamonds from space? Planetary destruction? Chris and Emily are totally up for that.