One thing we all know about the Sun: it’s incredibly hot. The surface (the outermost “layer” of the Sun that we can see) is 10,340 degrees Fahrenheit (F), and the core (which we can’t see) is 27 MILLION degrees F. There’s another part of the Sun that lies between the surface and us: it’s the outermost “atmosphere”, called the corona.It’s some 300 times hotter than the surface. How can something farther away and out in space be hotter? You would think it would actually be cooling off the farther away it gets from the Sun. This question of how the corona gets so hot has kept solar scientists busy for a long time, trying to find an answer. It was once assumed that the corona heated gradually, but the cause of the heating was a mystery. The Sun is heated from within by a process called fusion. The core is a nuclear furnace, fusing atoms of hydrogen together to make atoms of helium. The process releases heat and light, which travel through the Sun’s layers until they escape from the photosphere. The atmosphere, including the corona, lie above that. It should be cooler, but it’s not. So, what could possibly heat the corona? One answer is nanoflares. These are tiny cousins of the big solar flares that we detect erupting from the Sun. Flares are sudden flashes of brightness from the Sun’s surface. They release incredible amounts of energy and radiation. Sometimes flares are also accompanied by massive releases of superheated plasma from the Sun called coronal mass ejections. These outbursts can cause what’s called “space weather” (such as displays of northern and southern lights) at Earth and other planets. Nanoflares are a different breed of solar flare. First, they erupt constantly, crackling along like countless little hydrogen bombs. Second, they are very, very hot, getting up to 18 million degrees Fahrenheit. That’s hotter than the corona, which is usually a few million degrees F. Think of them as a very hot soup, bubbling along on the surface of a stove, warming the atmosphere above it. With nanoflares, the combined heating of all those constantly blowing tiny explosions (which are as powerful as 10-megaton hydrogen bomb explosions) is likely why the coronosphere is so hot.