Here comes the sun – exploring the energy chain
We all know that energy is a big deal. Life on Earth depends on various forms of energy to survive.
In every case, the sun is the primary source. There is direct benefit from the sun warming the Earth to make it habitable and other sources in the form of plants and animals. For example, burning wood effectively releases the solar energy stored by a tree, and we get energy by consuming both plants and animals.
Crude oil and natural gas are the result of dead sea animals (plankton) settling to the bottom of the ocean some hundreds of millions of years ago. Coal was formed by decaying plants in ancient swamps. Both types of fossil fuels were produced through geologic processes where the material was covered, heated and subjected to intense pressure in an oxygen-free environment over a very long time.
We can extract the stored solar energy via oxidation, i.e., burning, releasing the energy that binds the molecules together. I have been known to refer to fossil fuels as “dead dinosaurs,” but only as a joke. It’s not true.
Other forms of energy you might think of such as wind, hydro, wave, geothermal and solar cells are also examples of converted solar energy. But what about nuclear? Hang on.
Transformations of solar energy
All other forms of energy are transformations of solar energy. That begs the question: “Where does the sun’s energy come from?”
Nuclear fusion is a process where two light nuclei are combined to produce a heavier nucleus along with other subatomic particles such as protons, neutrons and energy. All the elements up to iron are created this way. All the elements heavier than iron require energy input.
If a star has sufficient mass (much greater than our sun), there is a point during its life cycle where the core collapses and it explodes in an event called a supernova – creating heavier elements that are scattered over the universe and eventually captured in dust clouds.
Under the influence of gravity, these clouds condensed to form new stars and planets, including our own. It’s the source of heavy elements used in fission reactors. Nuclear fission is where a heavy nucleus, uranium for instance, is broken apart into smaller nuclei, releasing the energy that bound them together. Just the opposite of fusion. In that sense, it is like burning fossil fuels but on the nuclear level. Nuclear fission also originates with stars or suns.
Mimicking the sun
For decades, scientists have been trying to find ways to reproduce fusion reactions on Earth, but on a much smaller scale, of course. Mimicking the sun is no easy task. The sun is a plasma, a hot gas (27 million degrees in the core) made up of bare nuclei and electrons. Remember that nuclei are bound together via the strong nuclear force, and it has a very short range. But the two nuclei have a positive electrical charge and repel each other. The challenge is to overcome the repulsive force and get the nuclei close enough for the strong force to take over.
The sun’s advantage is that it is massive, so gravity, despite being the weakest force in the universe, does all the work of heating the atoms and creating a plasma that is hot enough and dense enough to overcome the electromagnetic repulsion to fuse the nuclei and release energy. Fortunately for us, this will go on for a very long time.
Next time, I’ll look at some ways scientists are trying to create a sun on the Earth. Hint: It’s not so easy.
Steve Gourlay
Steve Gourlay is a career scientist with a PhD in experimental particle physics. He recently retired after working at the Fermi National Accelerator Laboratory, CERN (the European Center for Nuclear Research) and the Lawrence Berkeley National Laboratory. Send questions and comments to him at sgpntz@outlook.com.