* Astronomy

Crystals found in comets could be the remnants of stellar burps.
We know that half the dust inside comets is crystalline, but where did it come from? The dust in the gas cloud that formed comets and the rest of the solar system is thought to consist of amorphous glass-like grains instead.
In January 2008, Attila Juhász of the Max Planck Institute for Astronomy in Heidelberg, Germany, and colleagues, studied the infrared light given off before and after an outburst of the young star EX Lupi, which allowed them to infer the chemical composition of the dust surrounding the star.

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Swathes of dark comets may be prowling the solar system, posing a deadly threat to Earth.
Hazardous comets and asteroids are monitored by various space agencies under an umbrella effort known as Spaceguard. The vast majority of objects found so far are rocky asteroids. Yet UK-based astronomers Bill Napier at Cardiff University and David Asher at Armagh Observatory in Northern Ireland claim that many comets could be going undetected.

"There is a case to be made that dark, dormant comets are a significant but largely unseen hazard" - Bill Napier.

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Title: The chemical diversity of comets
Authors: J. Crovisier, N. Biver, D. Bockelée-Morvan, J. Boissier, P. Colom, D.C. Lis

A fundamental question in cometary science is whether the different dynamical classes of comets have different chemical compositions, which would reflect different initial conditions. From the ground or Earth orbit, radio and infrared spectroscopic observations of a now significant sample of comets indeed reveal deep differences in the relative abundances of cometary ices. However, no obvious correlation with dynamical classes is found. Further results come, or are expected, from space exploration. Such investigations, by nature limited to a small number of objects, are unfortunately focussed on short-period comets (mainly Jupiter-family). But these in situ studies provide "ground truth" for remote sensing. We discuss the chemical differences in comets from our database of spectroscopic radio observations, which has been recently enriched by several Jupiter-family and Halley-type comets.

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Observable Comets (2009 Jan. 29.0 TT)

MPEC 2009 -A62