Some observatories — like the recently collapsed Arecibo Telescope in Puerto Rico — examine nearby objects by bouncing radio light off of them. A new study has now improved how we analyze these observations to learn about near-Earth asteroids.
Clues from Reflections
There’s plenty we can learn about the universe from passive radio astronomy, in which we observe the radio signals emitted by distant sources. But when it comes to objects that lie near the Earth, we have another option: active radio astronomy.
Asteroid surfaces are complex, as evidenced by this up-close image from OSIRIS-REx of the surface regolith of asteroid Bennu. [NASA]With radar astronomy, we’re in the driver’s seat: we send a beam of radio light in the direction of our target — perhaps a close planet like Venus, or a nearby asteroid — and then observe the reflected light that returns to us. By measuring timing differences in the reflected signal, we can map out the shape of the object and its motion.
What’s more, measurements of the polarization of the reflected light — the direction the light waves are vibrating — tell us about how the light was scattered from the surface and near-surface of the body. ...