Did you know that comets are dirty? I know we often describe them as “dirty snowballs,” but most of us underestimate just how filthy these icy solar system bodies are. In fact, the dust spewed from a comet can actually be a hazard to visiting spacecraft. So, a team of astronomers from the Max Planck Institute for Solar System Research have devised a way to map out the dirty danger zones.
Comets contain rocks and dust, but also volatile materials like frozen water and carbon dioxide. The volatiles can sublimate — or change from a solid to a gas without becoming a liquid — as the comet approaches the sun. This releases dust and gas that can often be seen in the comet’s spectacular tail.
The technique devised by Jean-Baptiste Vincent, Hermann Böhnhardt, and Luisa Maria Lara uses both comet images and computer modeling. First, they input the best estimate of the three-dimensional shape of the comet body by watching the brightness of it as it rotates. Then, they model possible active locations (regions on the comet that are “outgassing” volatiles into space), dust grain sizes, and jet velocities, tweaking the model until it matches up with images of the comet taken from Earth.
The researchers tested this method with Comet Tempel 1, which was visited by NASA’s Deep Impact mission in 2005. They compared the results of their model with images actually taken by the spacecraft to find that they were able to locate the dusty jets quite well. Now they will turn their attention to Comet Churyumov-Gerasimenko which can expect to receive a visit from the European Space Agency’s Rosetta mission in 2014.
You can see for yourself just how dirty a comet can be my making your own! I recently did this as part of an activity for Dark Skies, Bright Kids, a local outreach program. Our kids had a blast mushing comets together with water, dirt, corn syrup, and dry ice to freeze it all together. (Okay, we did the actual mushing since kids should NOT handle dry ice.) So it’s a good thing that some astronomers are looking out for the health of our spacecraft with all that dust about!
If you want to make your own comet, Dark Skies, Bright Kids have instructions you can download: Comet – Physical Analog (PDF).
Images: (Top) An image of Tempel 1 on the left, compared to the model result on the right. Instituto de Astrofisica de Andalucia (Luisa Maria Lara)/MPS. (Bottom) A hand-held “comet”! DSBK