Monitoring Outbursting Comets
Comets are unpredictable things and, when you think about it, this is hardly surprising. There is no design specification for a comet as it is just an object that looks fuzzy when seen from a very long distance away. Any celestial object, of any size, that vents dust and gas when it gets hot is classified as a comet. Of course, in practice there is a size limit because truly massive planet sized objects will hold onto their gases by gravitational force even when close to the Sun, but typical cometary nuclei from, say, 1–60 km in diameter will not have any significant gravitational power. The images of cometary nuclei taken by space probes show objects which look quite similar to asteroids, at least when seen at close range. Of course, when hundreds of millions of kilometers away, the nucleus becomes an infinitesimal point and we just see a sheet of dust or gas, illuminated by sunlight and projected against the vast blackness of space. Professional astronomers have complex formulae they can use to give a rough estimate of, for example, the cometary water production rate based on the intensities of strong molecular emissions detected spectroscopically. Some also have very rough estimation formulae to predict water output rates based on the magnitude of a comet imaged in different wavebands.