Sonic Boom-Breaking the sound barrier 
*

*What actually is a sonic boom? 

*and what makes a bodies motion trigger the sonic boom? 

*and is it possible to create sonic booms in solids? Just wondering.
 A: 
  
*
  
*What actually is a sonic boom?
  

A sonic boom is just an abrupt increase in pressure caused by an object (often called a piston in shock physics) moving faster than the speed of sound in the medium producing a shock wave.
Note that the medium here is the Earth's atmosphere but shock waves can be produced in space as well, e.g., see https://physics.stackexchange.com/a/210097/59023, https://physics.stackexchange.com/a/139436/59023, and https://physics.stackexchange.com/a/179057/59023 for discussion of different types of sound speeds.


  
*and what makes a bodies motion trigger the sonic boom?
  

The shock wave itself is an abrupt/discontinuous change in pressure, which your ears interpret as the sonic boom.


  
*and is it possible to create sonic booms in solids?
  

Yes, well shock waves can certainly be produced within solids.  It is also possible, in principle, to hit a solid on one side hard enough to generate an internal shock wave that can propagate out of the solid on the opposite side.  Thus, the response of the solid material to the initial impact can produce both an internal and external shock wave.  The external shock wave could be heard as a sonic boom.
I should note that to produce the external shock wave I describe above, one would need to generate a significant amount of force on the solid object because I suspect a great deal of energy would be lost during propagation through the solid and much reflected at the solid-air boundary.  I have not gone through any hand-wavy estimates but I suspect many metals/alloys could survive the initial impact and produce the scenario I describe above.
To see more details about how the impacting object produces internal pressures and potential shock waves, see https://physics.stackexchange.com/a/216180/59023.
References


*

*Zel'dovich, Ya.B., and Yu.P. Raizer (2002) Physics of Shock Waves and High-Temperature Hydrodynamic Phenomena, Ed. by W.D. Hayes and R.F. Probstein, Mineola, NY, Dover Publications, inc., The Dover Edition; ISBN-13: 978-0486420028.

*Whitham, G. B. (1999), Linear and Nonlinear Waves, New York, NY: John Wiley & Sons, Inc.; ISBN:0-471-35942-4.

A: There are plenty of answers on this site regarding the creation of sonic booms in air and I will point out this article Sonic Boom Wikipedia
Science Magazine
There is a  paper in "Science Magazine" that states, under certain conditions, the slippage between two granite blocks can travel with supersonic velocity, creating a "seismic sonic boom" - a conical shock wave The effect is responsible for certain type of earthquakes.

Seismic shear waves released by an earthquake typically far outpace motion along the fault surface. Occasionally, however, earthquakes along strike-slip faults appear to propagate so that the rupture velocity is faster than shear waves, creating a sort of sonic boom along the fault surface. Passelègue et al.  were able to reproduce and measure these so-called supershear ruptures in stick-slip experiments with two pieces of granite under high applied normal stress. Much like during a sonic boom when a plane travels faster than the speed of sound, the ruptures created a shock wave in the form of a Mach cone around the rupture front.

A: It is not possible to create sonic booms in solids for one reason. You cannot accelerate an object to the speed of sound in solids because its a solid. The molecules hinder it because they are packed too closely (which is the defintion of solid). Small particles such as electrons can have greater than sound speeds in solids (assuming they are lucky enough not to collide with other atoms) but they cannot produce sound because sound itself is oscillatory motion by molecules caused by an object's movement, electrons are too small to cause any disturbance.
