Subtitles section Play video Print subtitles At first glance, you would not think that high radioactivity would make a planet ideal for habitation. But new research reveals that massive doses of radiation might actually be essential for life outside our solar system. Okay, let's clarify here. Water makes possible all the chemical reactions for life here on Earth. So when we're looking for other life out in the universe, it's widely thought that the absolute most important thing a planet needs is… something like water. That can be any kind of liquid solvent, or a substance that other things dissolve into. Because of this, it's long been thought that a planet needs to be the right distance from its star in order to be considered 'habitable' — kind of a Goldilocks situation: not too close to fry in the heat of that star and have all its water sizzle off, and not so far that it's left out in the cold with only frozen water. This ideal distance from a star is what we call the 'habitable zone.' Many organizations, including NASA, search for planets outside of our solar system, called exoplanets, that may exist in this zone as they're the most likely candidates for being able to host life. But new research turns that idea on its head. A team used modeling to find that at a certain size and with a high enough level of radioactive decay, a planet may not need a star to make it habitable—maybe it's keeping itself warm instead. The key ingredient? Radioactive forms of elements called radionuclides. These are isotopes, or different kinds of familiar-sounding elements like uranium that are radioactive. And while radiation often has a negative connotation for being damaging to living things and different kinds of radiation can cause damage to varying degrees, one essential thing about radioactive decay is that it releases heat. In fact, there are all kinds of radioactive elements in Earth's crust and interior, and scientists actually estimate that about 50% of the heat given off by Earth is due to the radioactive decay of elements like uranium, thorium, and potassium! Is it getting hot in here, or is it just me? The team behind this latest news took that concept and asked the question: “Could this be enough to keep a planet without a star nice and toasty?” They modeled three different sources of heat for a starless planet: radioactivity from isotopes that take billions of years to decay, radioactivity from isotopes that only take hundreds of thousands of years to decay, and heat left over from the planet's formation process. The scientists' model allowed them to plug in different planet sizes, ages, and radionuclide abundances. Using the resulting calculated surface temperature, they then determined if that planet could host the life-giving liquid we're searching for. The solvents they considered were three of our Solar System's most common: water, ammonia, and ethane. Their results show that warming a planet enough to host water in liquid form (without that helpful heat from a star) would require about a thousand times more radioactive stuff, like uranium and thorium, than we have on and inside the Earth. That is a lot of radiation. Their calculations also showed that Earth-sized planets with about one hundred times Earth's abundance of radionuclides could keep ethane liquid for hundreds of millions of years. This research suggests that when we're looking for exoplanets that could host life, we now may not only have to search for those in the habitable zone of a star, but also radioactive, starless loners. It brings up three key questions: could life survive in these huge doses of radiation? Is it likely that a planet with this amount of radionuclides exists out there? And if it does, could we find it? As to the first question, it's kind of hard to picture the kind of multicellular life we're familiar with on Earth being able to withstand that kind of radiation. But our world's most extreme microbes may be the perfect example. There's actually a bunch of bacteria that are totally chill with ionizing radiation, and then there's Cryptococcus neoformans, which is a radiotrophic fungus that actually eats radiation. And as for being able to find a planet like this, burning from the inside out with a radioactive glow? Only time will tell. But with the latest generation of space telescopes being launched soon, like the James Webb, we'll be able to keep an eye out—all thanks to research like this that told us what we should be looking for in the first place. If you want more on exciting exoplanet finds, check out this video here. Keep coming back to Seeker for all your extraterrestrial hypotheses. If you have another astrobiological headline you want us to cover, let us know down in the comment below and as always, thanks so much for watching. I'll see you next time.