Our good friends at Bloomsbury Sigma have recently published The Planet Factory: Exoplanets and the Search for a Second Earth by astrophysicist, science communicator and author, Elizabeth Tasker. As you may know, we’re a fan of everything space-related, so we couldn’t be happier when we got the opportunity to have Professor Elizabeth Tasker introduce her book in a slightly unconventional way, in conversation with… her (interior) ‘headline-grabbing journalist’-self... just in time to close World Space Week.

 The Planet Factory’ sounds like a DIY Guide to building your own planet. Is this secretly the handbook from the planet-building world of Magrathea in The Hitch Hiker's Guide to the Galaxy?

It’s all true; the Magratheans were my target audience! The Planet Factory does walk you through how planets are made. We start with a dusty disc that circles young stars and end with a zoo of worlds more varied and strange than anything we've come up with in fiction.

But isn't this old news? We've got this planet right here that we're standing on [STAMPS FOOT]. And seven more orbiting the Sun. Surely we had this figured out decades ago?

 We did think we largely understood how planets formed until we began to discover worlds around other stars. These exoplanets blew these theories to pieces.

Sounds scandalous! Did anyone get fired?

 Science isn’t about immutable theories! We should always question our understanding and change our ideas to match new evidence.

Our Solar System has two types of planet: rocky worlds like the Earth and Mars and giant gas planets like Jupiter and Neptune. The gas giants all orbit the Sun at a greater distance than the rocky planets. This is because they must form where it is colder, so frozen ice can help bulk up their mass. We thought this would have to be true around all stars.

But in 1995, astronomers discovered 51 Pegasi-b; a Jupiter-sized planet orbiting its star at just 5% of the distance between the Sun and Earth. That is much closer than Mercury orbits the Sun! This was a new class of planet; a ‘hot Jupiter’.

How hot?!?

 1200 degrees celsius hot! 51 Pegasi-b orbits its star in just over four days, so a year on this planet lasts less than one week on Earth. Since there shouldn’t be enough building material so close to the star’s vaporising inferno to form a planet, we think 51 Pegasi-b changed its orbit after formation.

Like being born in Dundee but moving to a beach hut in the Caribbean?

 … close enough. The idea that planets could migrate had been suggested as early as the 1980s, but there was little evidence for it within our own Solar System. It wasn’t until the discovery of the hot Jupiters that astronomers began to realise this was a major sculptor of planetary system architecture.

So, you're saying we're weird?

 Actually, we don’t know! Planets are easier to detect if they orbit close to their star. This means we may be seeing only the inner parts of planetary systems. But we do know our Solar System is missing the most common class of exoplanet that has been discovered: a super Earth.

The planet equivalent of super-sized fast-food meal options?

 Maybe… or maybe not. Super Earths are larger than the Earth but smaller than Neptune, our smallest gas giant planet. They could either be mega rocky worlds or mini gaseous ones or neither of the above. A few super Earths have intermediate densities, suggesting they may be drowning under a global ocean or have an atmosphere thick with volcanic ash.

Those are some strange worlds.

 And they’re not even the strangest. We’ve found planets orbiting two stars like Star Wars’ Tatooine, planets with no star at all that drift alone through the blackness of space and planets made from the remains of a star that was shredded by a dead stellar twin.

OK, that’s far too macabre. What about all these other Earths we’ve discovered? Glistening lakes, rolling hills and seasonal frappuccinos. Do they also go all-pumpkin for autumn?

 Whoa, slow down! We have discovered many planets that are similar to Earth in size, but we have no idea what their surface would be like. We usually know only the minimum possible mass of the planet or its physical size, and its distance from the star.

Ah, but what about those planets in the ‘Habitable Zone’? It’s clearly a zone that is habitable, right?

 Sorry to be a grinch but the ‘Habitable Zone’ is just where a planet would receive a similar amount of starlight to the Earth. If the planet is an exact Earth clone, then it could support liquid water on the surface. But a different world may have a surface that is too hot or too cold or too dry, even within the Habitable Zone. In the book, I call this the ‘Temperate Zone’ because it really has nothing to do with habitability!

 At the moment, we just don’t know enough about these Earth-sized planets to determine if they are at all Earth-like.

You are the grinch that stole Earth 2.0!

But this will change in the future! New telescopes are aiming to detect gases in an exoplanet’s atmosphere. This will give us a whiff of what is happening on the surface and maybe even if life is down there.

With The Planet Factory, I aim to show what we have discovered about exoplanets. How they form, where they form and how they may be different or similar to our Earth.

We now know our planet is one of a myriad of worlds in our Galaxy. We are teetering on the brink of finding out what some of these are truly like. The answer may be that many are habitable, but these could be very unlike our Earth.

The Planet Factory: Exoplanets and the Search for a Second Earth is published by Bloomsbury Sigma and is available to buy now. Visit the Bloomsbury website and enter code BSA25 at the checkout to get 25% off.