July 14 – Elst-Pizarro: Asteroid or Comet?

Minor planet 7968 Elst-Pizarro was discovered by Eric W Elst and Guido Pizarro from photographic plates taken by Pizarro while he and his brother Oscar were working as assistants with the ESO Schmidt telescope at La Silla Observatory, on July 25, 1979. The discovery was reported by Elst, of the Royal Observatory, Uccle, Belgium, on August 7th. Comet 133P/Elst-Pizarro was discovered by M R S Hawkins and R H McNaught on July 14, 1996.  They are one and the same.

133P/Elst-Pizarro has characteristics of both an asteroid (for a start, it’s in the asteroid belt, with an orbit varying between 2.6 and 3.6 AU) and a comet (it sometimes has a tail). The tail suggests a non-asteroidal icy composition, although it is also possible that this is a rocky body that occasionally expresses dust due to the gas pressure of evaporating ice.  This is where I go off at a tangent to make sure we’re on the same wavelength with the word “express”.  Your small strong coffee is called an espresso because of the way the water is forced under pressure through the beans,  like so much ice from the surface of comet 133P/Elst-Pizarro (possibly) and has nothing to do with the speed of it’s drinking, or the way it makes you rush around like a lunatic for thirty minutes afterwards.  And while we’re on the subject, look up the origin of the name cappuccino. (End of pointless aside.)

The occasional nature of the tail doesn’t do much for E-P’s comet cred. It only tends to appear close to the perihelion of its 5.62 year journey around the Sun.