 Hello and welcome to the Habitable Zone Unplug where we explore the science behind the sci-fi. I'm Calico Field from the Media Relations Office at NASA's Jet Propulsion Laboratory. So today we're talking about the episode Goldilocks Paradox, and here to help us explore that episode are two astronomers, Dr. Robert Hurt, who is a visualization specialist and also the director of the episode, and Dr. Johanna Teske, who is an exoplanet scientist. Thank you both for being here. To start with the basics, can you tell me to a scientist what does the habitable zone mean? So right now, scientists think of the habitable zone as where water could be liquid on the surface of an earthish-sized planet. To have that, you need to be not too close to the star that the water would be steam, but also not too far away that it would be ice on the surface. So it's about how far away and what type of star you have. So in this episode, our space explorers discover two very promising planets, but actually neither of them turns out to be very hospitable to humans. So Robert, what were the main science concepts that you wanted to get across in this episode? Sure, the idea of the whole series, in fact, is to really dig at this idea of what really does a habitable zone mean, and look at all the different parameters that have to be lined up just right in order for a planet to truly be habitable, even if it's sitting in the right spot. So the idea behind this one was to look at composition. You know, that you need a planet that not only is in the habitable zone at the right location, but it actually has to have the right mix of water and gases on the surface to support oceans. In this case, the idea is we get something that's just right in terms of composition, but in the wrong location, and something that's perfect location that just doesn't have the right stuff. Yeah, and so in the episode, one of the planets cast notes that it is the same distance from its star as Earth is to the sun, and they detect water, but it's not actually habitable, it doesn't have oceans. So tell me why that would be. So, as you noted, this planet appears to be to have water, but that distance that the planet is away from the star in that system actually is too far away for that water to be liquid. They show an image of the star being slightly smaller and cooler than the sun. So that means that at the same distance as Earth, the planet is actually receiving less heat or radiation from the star, and so the water can't be liquid, it's ice. And then the second planet is in the habitable zone of its star, but it also isn't habitable, doesn't have oceans. So Robert, why is that? Well, again, that was just the conspiring as a writer and a scientist to imagine a world where the composition is wrong to have the right mix of volatiles that you would need to support liquid water on the surface. In this case, the idea would be to come up with a planet that has a higher density than the Earth and is maybe a little more biased towards the heavier elements and doesn't have the right mix of light elements to give us the oceans. Alright, we're going to take a break, but in our next video, we'll dive deeper into how the art in this episode is informed by actual science. I hope you'll join us.