The Mesosphere

The mesosphere may be one of the most mysterious layers of the Earth’s atmosphere but there is a good chance you have witnessed its power with your own eyes. If you have seen shooting stars burn brightly, you’ve peered into the mesosphere.

The mesosphere sits between 50 and 85 kilometers above the Earth. Below it, planes fly in the stratosphere. Above it, satellites orbit in the thermosphere. Not quite Earth and not quite space, it is almost a crossing point between the two.

When extraterrestrial objects such as meteors enter the Earth’s atmosphere they start to heat up as they cut through the mesosphere. Moving at high speeds the friction between these objects and the air molecules in the mesosphere generate a heat intense enough to burn. The glow we see streaking across the night sky is that object as it burns up in the mesosphere.

The mesosphere also dazzles us with:

  • Nightglow or airglow, a faint luminescence of air molecules and atoms in the mesosphere as they absorb solar ultraviolet and X-radiation. This same phenomenon has been seen in the atmosphere of Mars.
  • A type of lightning called sprites which sometimes appears in the mesosphere above thunderstorms. 
  • Strange, high-altitude clouds called noctilucent clouds that sometimes form in the mesosphere near the North and South Poles. They appear when material from meteors linger causing a relatively high concentration of iron and other metal atoms.

The mesosphere has been particularly difficult for scientists to study. It is too high for airplanes and balloons to take measurements and too low for satellites to explore. The most common way scientists have studied the mesosphere up until now is by sending rockets up into it that collect samples and then fall back to Earth.

Fast fact: The highest point of the mesosphere is also the atmosphere’s coldest point. Because the air is so thin fewer air molecules can absorb the electromagnetic radiation from the sun. Temperatures can be as cold as minus -140 degrees Celsius. And winds can reach 160 kilometers per hour. 

Researchers are hoping that a fleet of micro flyers, tiny levitating discs, will be able to help them explore our mysterious mesosphere. Made of tiny disks of mylar on top (the shiny lightweight material used to make party balloons) and carbon nanotubes on the bottom (tubes of single-layer carbon atoms) they measure six millimeters wide.

The micro flyers rely on the heat generated by light from the sun to stay airborne. When the disks are exposed to bright light they heat up. As air molecules bounce off the disk, the disk transfers some of its warmth to the molecule, which makes the molecule move a little bit faster and push back on the disk. Because the carbon nanotubes are much better at transferring energy than the mylar there is more reaction at the bottom of the micro flyer. The air molecules bounce off the bottom of the disk faster than off the top, in effect pushing harder on the bottom and lifting the craft up.

What scientists don’t know is how it will deal with the mesosphere’s high winds, cold temperatures, and frequent sunspots. The disks are also so delicate that molecules bouncing off them may make them crinkle. 

If successful these micro flyers may be a way for us to explore other planets such as Mars which has an atmosphere like the mesosphere.

Article originally published in Brainspace Magazine Summer 2021

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