Quantum Effects on Asteroids
By: Thomas Albin
Tags: Astronomy, Space, Asteroids, Science, Astrophysics

The Yarkovsky Effect

Around 1900 the Polish-Russian civil engineer Ivan Osipovich Yarkovsky described a theory about thermal effects on small Solar System bodies (like asteroids or meteoroids). However, his theory remained unknown and unnoticed for several decades. In the 70s / 80s the so called Yarkovsky Effect was re-introduced and became also the basic concept for further theories that will be described in future articles.

Let’s take a look at the following schematic drawing that shall help us to understand the effect:

An asteroid (grey) revolves the Sun (yellow) on an orbit (white dotted line). The Sun emits radiation (yellow arrows) that is absorbed and reflected by the asteroid’s surface.

Now let’s consider the rotation of the asteroid around its axis and imagine standing on the surface of this tiny world (in a well protecting space suit). Similar as on our home planet there are different daytimes, like the sunrise, the sunset, the night and so on. An asteroid day depends on the asteroid’s rotation. Some rotate extremely fast and would literally eject you into outer space. A comprehensive list can be found here:

During the night, the surface points away from the Sun. The surface cools down and reaches a minimum temperature before dawn. The sun rises and you and your space suit as well as the rocky surface heat up. The radiation input changes, depending on the day time and corresponding Sun elevation above the imaginary horizon you see. It’s noon now; the surface is fully illuminated and from now on, the Sun starts to set and the night starts again …

This rotation, its daytimes and changing heat fluxes cause a non-uniform distribution of the asteroid’s temperature. In simple words:

The dawn side is cold (indicated with a blue arrow)

The dusk side is warm (indicated with a red arrow)

The Yarkovsky Effect explained in a schematic drawing: An asteroid (grey) orbits (white dotted line) the Sun (yellow). The asteroid rotates around its own axis causing different daytimes on the asteroid. The absorbed radiation from the Sun (yellow arrows) cause a heating on the day side. At night, the asteroid cools down. This leads to a colder “dawn” and warmer “dusk” side as indicated with a blue and red arrow, respectively. Image Credit: T. Albin.

This temperature difference is linked with different thermal radiation properties. The energy and distribution and consequently linked photon radiation pressure is slightly different between both “dusk” and “dawn” sides. Net, the different radiation pressure components lead to a force that is tangential w.r.t. the asteroid’s path; pointing from the warmer to the colder side. In our example: the resulting force points to the blue arrow direction. The asteroid’s orbital elements change and (in this case) the asteroid moves slowly inwards, towards the Sun. Note: If the asteroid’s rotations would be the other way round, the asteroid would move outwards.

This movement is rather slow. Very slow. Eventually the asteroid gets a set of orbital elements that is e.g., in resonance with one of the major planets. The resonance becomes the dominant effect and alters the orbital properties even more.