The dust bunnies that built our planet - Lorin Swint Matthews
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Stars are very hot balls of ionized gas, or plasma. But plasma isn’t only found in stars: it fills the space between stars and even the space between galaxies. More than 99% of the visible universe is made of plasma. Plasma has free electrons and ions which allows it conduct electricity and carry magnetic fields. These electric and magnetic fields help sculpt the beautiful structure observed in nebulae produced by dying stars, such as the Ant nebula, the Cat’s Eye Nebula, and the Butterfly Nebula. The Hubble Space Telescope has many more images of nebulae on its website.
Here on earth, plasma is the matter found in flames, lightning bolts, neon signs, and the northern and southern lights, or aurora. Plasma can even be used as an energy source. Scientists are currently working on making very hot, dense plasmas to fuse hydrogen atoms, the same process that produces energy in the sun.
Protoplanetary disks are the leftover material around newborn stars and are the regions where planets form. The very first pictures of protoplanetary disks were taken in 1995 by the Hubble Space Telescope. Planet formation is very rapid, only taking ten million years compared to a star’s lifetime of several billions of years. However, this is much too long for us to watch a solar system form. In order to learn how solar systems evolve, astronomers need to compare data from lots of disks which are at different point in their evolution. Astronomers have now found thousands of these disks. Newer telescopes, such as the Atacama Large Millimeter Array (ALMA) can produce high-resolution images of these disks, revealing details such as gaps and rings, which may have been carved out by newly formed planets.
Charged dust isn’t just important as a step in the formation of planets. Dust is found everywhere in the universe. It can be seen in giant molecular clouds where stars are born, comet tails, and planetary rings. Dust coats the surface of the moon and Mars, which can cause problems for visiting rovers or astronauts. A dust grain becomes charged when electrons and ions from the plasma run into it. Since electrons are much less massive than ions, they move much faster and run into the dust more often than ions do. Thus the dust is usually negatively charged. However, dust can also become charged by high energy UV photons knocking electrons off of the dust, leaving the dust with a positive charge.
On airless bodies like the moon and asteroids, dust which has been charged by the electrons and ions in the solar wind or by exposure to sunlight can hop around. Watch this movie to see experiments here on earth which demonstrate how the charged dust is transported. If you would like to perform your own experiment to see electrostatic transport of small particles, try this: put a few spoonfuls of sugar into a Styrofoam cup. Use a plastic spoon to scoop up some of the sugar and hold it near the edge of the cup. You should be able to observe grains of sugar fly from the spoon to stick to the rim of the cup.
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