Orbital elements (inclination vs. semi-major axis) of objects in the asteroid main belt. The small dots represent the background population of main belt asteroids (only numbered ones are represented for clarity; proper elements were used to put collisional families in evidence as dense clouds; source: the Asteroid Dynamics Site, http://hamilton.dm.unipi.it/astdys/). The known main belt comets are represented as large symbols: squares indicate objects with extended activity; those that showed activity at more than one perihelion are plotted in green; 176P, which did not display activity when returning to perihelion, is marked in cyan. The inclination of P/2010 R2 is off scale (i = 21.39); its a is marked by a square with an arrow at the top of the plot. Triangles indicate objects that showed only a very brief activity episode. P5 is indicated by the large red circle to the left.