Sunlight could keep sensors floating in the sky NASA Photo/Alamy
Small sensors powered only by sunlight could float in the stratosphere indefinitely and make weather-related measurements.
There is a known effect for levitating flat objects with two sides called photophoresis. This occurs when one of the sides absorbs lots of light and the other very little, creating a difference in temperature. Just like how temperature differences in the atmosphere cause winds, this temperature gradient makes molecules move in such a way as to create a lifting force on the object.
