[MUSIC] On Earth, we are protected from much of the radiation that is bombarding us from deep space and our Sun. Both the atmosphere and the magnetic force field generated by a molten core known as the magnetosphere will shield us from the worst effects of radiation. The international space station has almost no atmospheric protection and very reduced magnetosphere shielding, which means that during a year on board, astronauts can receive hundreds of times the recommended maximum annual dosage of radiation. A trip to Mars would last even longer, and completely remove the astronauts from the protection of the Earth's atmosphere and magnetosphere for the journey between the planets. But why is radiation so deadly? Radiation releases high amounts of energy and high energy particles. This energy will react with oxygen in the molecules to form reactive oxygen species. In short, too many reactive oxygen species can build up and cause damage. In acute radiation sickness, this build up overwhelms the body's natural ability to remove these oxygen species, and can lead to nausea, internal bleeding, and death if the levels ever become too high. In space, the levels of radiation will rarely reach these extremes. Instead, we are worried about the hazards of repeated and constant exposures, leading to reformations of reactive oxygen species, which can slowly lead to DNA damage. DNA is important because it provides the information to build new cells and repair damage to existing cells. Since it is copied from one cell to the next, changes caused by damage and inaccurate repairs can accumulate across a person's lifespan. If these changes, known as mutations, become too much, they will compromise the ability of the cells to grow and replenish themselves, or even corrupt them. Some parts of the body rarely make new cells after they are initially formed. A current debate within science asks if adults are able to form new neurons inside the brain and spinal cord in a process known as neurogenesis. Despite the contradictory studies, it is clear that neurogenesis drops too little to none after puberty, meaning neuron replacement is severely limited in adulthood. Similarly, cells of the muscles of the heart, skeletal muscles, and lens of the eye are rarely replaced in adulthood. When these tissues are damaged by radiation or reactive oxygen species, scar tissue forms, potentially causing permanent loss of function because new cells will not replace the damaged ones. At the other extreme, other parts of the human body, such as the linings of the digestive system, and lungs, skin, liver, and blood cells are constantly dying and replacing themselves. Radiation to these cells will destroy them, but new cells can be made to replace them. Instead, we worry about damage to the cells that produce them. Radiation here can lead to the development of cancers, where quickly replacing tissues can become corrupted and fight with the rest of the body for resources. You've likely heard of lung cancer, skin cancers, and even leukemia or cancer in the blood. All of the tissues that often become cancerous quickly replace themselves. To further highlight the distinction in these tissues, when people think of brain cancers, most of the time, it's not actually the neurons in the brain that becomes cancerous. Instead, the glial cells which surround, protect, and feed the neurons become cancerous in glioblastomas. In either context, radiation exposure will lead to perhaps irreversible damage or death. Cancers are especially worrying in a space context, because they require extensive testing and chemotherapies, or further radiation to eliminate or treat them. However, because of the limited resources and the bone and muscle atrophy caused by microgravity, treatment and recovery seem impossible. To fight the heightened levels of radiation in space, aerospace engineers work to design vehicles that will shield deep space travelers for most of the radiation. One strategy is to choose certain materials to line the walls of the ship to prevent radiation from penetrating and affecting the astronauts. Much like that lead shirt that you wear when you receive x-rays, specific materials may shield astronauts from most of the radiation. One such material that is especially good at stopping many different types of radiation is water. Since it will be necessary to bring a lot of water if astronauts are to visit Mars, one exciting idea is to store it surrounding the crew quarters and ward off most of the radiation. >> Now to make a technical point clear, there have been a few times in this course so far where we push up our glasses to say, actually, and make a fine point. And this is a point where I'll add a little bit of context around what we mean when we say, the radiation of space. Solar bodies, like the Sun, through nuclear fusion, generate electromagnetic radiation, which is a form of ionizing radiation. This makes up the light that reaches us from the Sun or other stars. However, other forms of radiation, namely alpha and beta particles, do not have enough energy to escape from the electromagnetic and gravitational pulls of the rest of the Sun. And instead, will react with other nuclei to provide the continual fusion reaction in the core of the Sun. Electrons and protons still leave our sun in solar winds, which leads to an interesting question of how. Technically most of the electrons and protons that are released by the Sun are not true radioactive decay. That is particles emitted by unstable elements undergoing nuclear fusion, nuclear fission, or the absorption and ejection of electromagnetic energy. Instead, the nuclear fusion inside the Sun first makes it very hot. This leads to the formation of plasma, where protons, electrons, and neutrons become separated in a superheated soup. The Sun generates magnetic fields which align the protons and electrons in its atmosphere, known as the corona. As the Sun spins, the protons and electrons in the corona may be ejected as solar winds. These solar winds scatter outwards and shower the earth in electrons and protons, which are redirected or repelled by the magnetosphere, and neutrons, which can be stopped when they collide with water vapor. As the magnetosphere extends from the molten iron core and has its dipoles at the north and south poles, these electrons and protons travel towards these poles. During a large solar wind, these electrons and protons flood the earth, and they are pulled into the atmosphere at the north and south poles. These excited particles can form plasma and provide energy to nitrogen and oxygen gas, exciting them and leading the gases to admit bright blue, green, and red lights. Thus, at the north pole, the aurora borealis, and at the south pole, the aurora australis, are formed. So here with me in Duke physics building, we have two different science experiments to illustrate the difference between the solar winds, and then the classic radioactive decay. And so the solar winds is largely composed of protons and electrons. And so here in front of me, I actually have an electron gun inside of a large magnetic field produced by these two coils. And so, the electrons will curve in on themselves, and as they move, they will excite the nitrogen gas, producing the blue glow much like the aurora borealis. To just show how they are electrons, here's a magnet, and I'll take it and I'll move it. This is distorting the magnetic field, and clearly the electrons are reacting, and they're showing kind of the strong movement. And so, if you think of Earth's magnetic field as moving, this is what the northern lights is a little bit, where the electrons are entering into the atmosphere and then producing this beautiful light show. These are energized particles. They can have an effect. They can have even dangerous effect on cells and living organisms if exposed to it. But it's not quite the same thing when we think of the Chernobyl disaster and the radiation involved there. And so when we speak of that radiation really, we can take a Geiger counter and we can measure how much energy is being detected. And so maybe you've seen this in movies, where this device will make a clicking noise if we have really true presence of decay and radiation. And so here, we don't see anything, and the audio isn't showing much of any decay. What we will see is when we turn over here. This is a piece of Fiestaware from the early mid 20th century. And it was dyed particularly in orange red color, and they use the uranium in the dye. And so as we get close to this, the Geiger counter will start clicking much more excitedly, showing that this is the type of radiation most people think of. When we talk about the radiation we're worried about in space, we're thinking more of high energy particles. So not quite your typical radiation, your radioactive decay, but high energy particles, that still can do lots and lots of damage even though it's not quite the same thing as what comes across when atom breaks apart.
