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.

TESS made it! The little satellite with the big heart is now in space, gradually getting into its final orbit to start gathering data. And Emily is excited, because alongside all the exoplanet data TESS will be taking, it's going to collect all sorts of information about her favourite topic: Wobbling Stars. Or as she would prefer to call it, Asteroseismology.

After a quick listener question from Graham in Highfields, Australia, this week’s show is all about TESS: The Transiting Exoplanet Survey Satellite.

TESS is a brand new space telescope that, at the time of recording, was sitting atop a SpaceX Falcon 9 rocket, preparing for launch. Once in orbit, TESS will spend two years scanning almost the entire sky searching for exoplanets around stars in our local area of the Milky Way Galaxy.

Emily is particularly excited because the data TESS will send back will also contain loads of info for astronomers interested in variable stars, her own area of expertise.

So keep your fingers and toes crossed for a safe launch and successful mission. Go TESS go!

Syzygy is a brand new podcast, in which science nerd Chris Stewart and York astronomer Emily Brunsden talk about the latest news from across the universe. Here's a sneak peek at what's coming.