Short answer ; Maybe it does not diverge from orbit, but it will certainly harm.
The exosphere is the top layer of the atmosphere, 10 thousand km thick. So it’s a very thick layer. It contains traces of hydrogen and helium atoms, but at the top, this content gradually dilutes and merges with space. So it does not contain air that can be inhaled. In fact, during the Cold War between the USA and Russia, both sides tried various nuclear weapons in the upper layers of the atmosphere.
It was the nuclear bomb equivalent to the 1.4 megaton TNT that the US exploded on July 9, 1962 in the “Starfish Prime” mission. But this explosion took place at an altitude of 400 km, that is, the Thermosphere, which was the layer before the Exosphere. The bomb produced a larger electromagnetic pulse than expected.
The electromagnetic waves emitted after the explosion radiate outward from the explosion center and react with the gases in that layer of the atmosphere and activate the electrons. The result is an electromagnetic pulse that acts on the ground, which at best damages electronic devices.
In that test, telephone plants were damaged in Hawaii, 1400 km away, the engines of the cars in operation stopped, fuses and street lamps exploded. In such explosions, besides shock waves, thermal radiation and nuclear radiation are also released. Wherever the electromagnetic pulse will affect is not a predictable situation.
It can move in any direction and it cannot be calculated which region it will affect on Earth. However, a top layer is different in nature. Since the exosphere resembles outer space, that is, it contains no breathable air, we seem to explode the content in space. Instead of the mushroom clouds you see above, something else appears.
The effect of the nuclear explosion in space cannot spread over a large area. In the world, a giant flame ball is formed in a few-kiloton explosion, and its effect spreads over several kilometers. If the same happens in space, this time an effect spreading to 1-2 meters with a small ball of flame is observed. Then, the content that appeared in the explosion freezes immediately. Since atoms and molecules are rare in the exosphere, hydrogen and helium do not act like gas.
So what a blast of a few megatons would be high energy radiation would be. So gamma and X rays. Since the exosphere does not contain atmospheric content, there is nothing to stop this radiation from spreading. In summary, the explosion resembles the shape of the sphere, and the light released with the radiation waves spreads easily and rapidly.
If we look at the surface of the planet at that time, we can see light fluctuations. These are just like the northern lights. Because charged particles emitted from the explosion interact with the Earth’s magnetic field.
Well, doesn’t electromagnetic pulse occur? Of course it occurs, and the impact can be enormous. In addition, the radioactive content emerging in the explosion leaks to the lower layers of the atmosphere and reaches the Earth.